Vitamins - Deficiency and Toxicity

Vitamins are essential nutrients that are active in metabolism and energy production and may function as enzymatic cofactors and antioxidants. With the exception of vitamin D, vitamins are not synthesized in the body and must be ingested regularly to maintain health. Vitamin deficiency or excess can lead to disease, and poor diet or disease can lead to vitamin deficiency. Vitamins may be either water soluble (B vitamins and vitamin C) or fat soluble (vitamins A, D, E, and K); fat-soluble vitamins are not cleared as readily from the body and thus present an increased risk of toxicity. Laboratory testing is used to assess the nutritional status (deficiency, sufficiency, and toxicity) of particular vitamins, including status in response to therapeutic supplementation. 

Quick Answers for Clinicians

When should laboratory testing for vitamins be performed rather than, or in addition to, supplementation?

Although supplementation has conventionally been recommended instead of testing for many vitamins, particularly the water-soluble vitamins, this approach is not recommended for patients who have undergone gastric bypass surgery. Following gastric bypass, regular monitoring of vitamin concentrations is required. For more information, see the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic.

How should patients be prepared for vitamin testing?

For practical reasons, laboratories often perform vitamin testing in plasma or serum. Vitamin concentrations in plasma or serum, particularly water-soluble vitamin concentrations, may vary based on recent intake. Therefore, fasting is recommended so that the effect of recent vitamin intake will be minimized. Fasting for at least 8 hours is recommended, especially if patients are taking vitamin supplements.

What are the appropriate specimen storage and transport conditions for vitamin testing?

Many vitamins are light and heat labile and may degrade if not appropriately handled and stored, leading to inaccurate test results. For example, vitamin C is light, temperature, and oxidant sensitive, and therefore unstable in plasma.  Addition of a preservative before freezing is recommended, when feasible, for specimens being tested for vitamin C.  However, storage and transport requirements differ between laboratories and assays. Refer to your laboratory’s test directory for test-specific specimen storage and transport instructions.

Which specimen type is appropriate when ordering multiple vitamin tests simultaneously?

The appropriate sample for simultaneous vitamin testing depends on the specific tests being ordered. For example, vitamin B6 testing is frequently ordered in conjunction with thiamine (vitamin B1) testing. Although plasma can be used for B6 testing, B1 tests will not yield accurate results in plasma; thus, whole blood is the preferred specimen when ordering both tests. Refer to your laboratory for specimen type, storage, and transport instructions when ordering simultaneous vitamin tests.

Which methods are used to measure vitamins in body fluids?

Vitamins can be measured using both direct and indirect methods. Indirect assays determine vitamin sufficiency by assessing the physiological effect of the vitamin. Direct testing for vitamins in body fluids is performed using a variety of techniques. Immunoassays typically are not harmonized among vendors, and standard reference materials are not available. Measurement of individual vitamers using chromatographic separation and detection by spectrophotometry, fluorescence, electrochemistry, or mass spectrometry is specific and sufficiently sensitive to accurately quantify the small concentrations of vitamins found in body fluids.

What effect does biotin (vitamin B7) have on other laboratory tests?

Many commonly used laboratory tests (including thyroid hormone assays and other immunoassays) make use of biotin-streptavidin technology. High biotin intake, such as from biotin supplements, may interfere with these assays, leading to inaccurate test results. The U.S. Food and Drug Administration (FDA) recommends consideration of biotin interference when test results are incongruent with clinical presentation.  For more information, including a list of tests potentially affected by biotin interference, see the ARUP Laboratories Biotin Interference page.

Indications for Testing

Laboratory testing for vitamins is used to:

  • Assess nutritional status (deficiency, sufficiency, or toxicity)
  • Monitor therapeutic supplementation

Vitamin A

Vitamin A refers to a group of fat-soluble retinoids with the biological activity of all-trans retinol, including retinol, retinal, retinoic acid, and retinyl esters.  Vitamin A is best known for its role in vision and eye health, but it is also important for immunity and reproduction.    Vitamin A is found in animal foods, such as fish liver oils and liver, and occurs in the form of a carotenoid or provitamin A (eg, beta carotene) in plant foods, such as yellow- and orange-colored fruits and vegetables.   Carotenoids are metabolized into vitamin A within the body.  Vitamin A deficiency is the leading preventable cause of childhood blindness throughout the world and is associated with significant morbidity and mortality from common childhood infections.  Deficiency may arise from bariatric surgery, fat malabsorption disorders (eg, celiac disease, Crohn disease), cystic fibrosis, and liver disease.   Excessive preformed vitamin A in body stores (hypervitaminosis A) can occur as a result of chronic or acute excess intake, such as from consumption of supplements, and may lead to adverse consequences before symptoms become apparent. 

Signs and symptoms of deficiency Xerophthalmia, keratomalacia, nyctalopia, increased risk and severity of infection  
Signs and symptoms of toxicity

Acute: nausea, vomiting, headache, vertigo, blurred vision, loss of coordination  

Chronic: liver abnormalities, bone and skin changes, central nervous system issues  

During pregnancy: birth defects 

Laboratory Testing

Assessment of Status

Retinol or Associated Proteins in Serum or Plasma

Vitamin A concentration is tightly regulated in the circulation and may not decrease until liver stores are nearly depleted.   Serum or plasma concentrations of retinol (the main circulating form of vitamin A) and/or the proteins that circulate with it (particularly retinol-binding protein) are widely used and considered sufficient to determine vitamin A status.   Because retinol-binding protein is a negative acute-phase reactant, retinol concentration will decrease if inflammation is present; consider measurement of C-reactive protein (CRP) to distinguish between nutritional and inflammatory causes of reduced concentration.  Retinol-binding protein is also affected by liver disease, zinc deficiency, and protein malnutrition, all of which may lead to decreased plasma retinol concentration. 

Retinol Palmitate or Retinol Esters in Liver Tissue

The gold standard for the assessment of vitamin A status is evaluation of hepatic reserves via biopsy.  Hepatic reserves may also be indirectly assessed with plasma dose-response tests that involve evaluation of retinol in serum before and after administration of a small amount of vitamin A.   

Carotenoids in Plasma

Measurement of carotenoids (eg, beta [β]-carotene) in plasma can be a useful supplemental test for the assessment of vitamin A status but should not be used alone. 

Monitoring

Patients with a fat malabsorption disease who are receiving high-dose vitamin A supplementation should be monitored to verify proper dosing and avoid toxicity.

Patients with cystic fibrosis are particularly prone to malabsorption of fat-soluble vitamins, including vitamin A.  Many cystic fibrosis organizations recommend supplementation and careful monitoring. 

Regular monitoring is recommended for patients who have had bariatric surgery. Testing should also be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

Vitamin B1

Vitamin B1, or thiamine (thiamin), is a water-soluble vitamin that is important in energy metabolism.  Sources of thiamine include meat, fish, whole grains, and fortified products (including infant formula).  The primary active form of thiamine in the body is thiamine diphosphate (TDP, also known as thiamine pyrophosphate).  Risk factors for thiamine deficiency include alcohol dependence, bariatric surgery, malabsorption, older age, and HIV/AIDS.  Because plasma thiamine concentration does not directly reflect thiamine concentration in tissue, plasma testing is not recommended for nutritional assessment; TDP should be measured in whole blood or erythrocytes instead.

Signs and symptoms of deficiency Weight loss, muscle weakness, cardiac symptoms, beriberi (peripheral neuropathy; occasionally, congestive heart failure), Wernicke-Korsakoff syndrome (initially Wernicke’s encephalopathy, which is characterized by peripheral neuropathy and progresses to Korsakoff’s psychosis with memory loss and confabulation) 
Signs and symptoms of toxicity

None reported 

Laboratory Testing

Assessment of Status

Vitamin B6 testing is frequently ordered in conjunction with thiamine testing. Although plasma can be used for B6 testing, B1 tests will not yield accurate results in plasma; thus, whole blood is the preferred specimen when ordering both tests.

Thiamine Diphosphate in Erythrocytes or Whole Blood

TDP can be measured in erythrocytes or whole blood and is the preferred analyte for assessment of thiamine status.  Erythrocyte thiamine concentration reflects thiamine status, and whole blood concentration correlates well with erythrocyte concentration, especially when corrected for hemoglobin. 

Thiamine and Thiamine Monophosphate in Plasma or Serum

Free thiamine and thiamine monophosphate can be measured in plasma or serum.  However, concentrations in plasma reflect recent intake, not body stores.  Therefore, measurement of TDP in erythrocytes or whole blood is the preferred test for evaluating vitamin B1 stores.

Thiamine Transketolase Activity in Erythrocytes

Measurement of erythrocyte thiamine transketolase activity before and after TDP supplementation in erythrocyte hemolysates serves as an indirect measure of tissue thiamine stores.  A high concentration of unsaturated thiamine transketolase suggests deficiency.  This test is no longer routinely performed in the United States.

Thiamine in Urine

Although not widely used, tests for excreted thiamine in urine may help determine thiamine intake. However, urine thiamine concentration does not reflect tissue stores.  Urinary concentration of thiamine in a 4-hour specimen compared before and after a test load of thiamine may assist in determining thiamine status. 

Monitoring

Regular monitoring is recommended for patients who have had bariatric surgery. Testing should also be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

Serial measurements of thiamine (eg, in patients with Wernicke-Korsakoff syndrome) should be performed using the same assay, preferably using a whole blood specimen.

Vitamin B2

Vitamin B­2 (riboflavin) is a water-soluble vitamin that is a critical part of the flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) coenzymes, which are involved in energy production and numerous other metabolic and cellular functions.  Sources of riboflavin include organ meats, lean meats, eggs, milk, green vegetables, and fortified grain products.  Risk factors for riboflavin deficiency include endocrine disorders (eg, thyroid hormone insufficiency), vegan diet, vegetarian diet (in athletes), low consumption of meat or dairy products during pregnancy, and riboflavin transporter deficiency neuropathy.  Riboflavin deficiency is often associated with deficiency in other B vitamins because riboflavin plays a role in the activation of vitamins B3 and B6.  Testing of riboflavin status is not routinely performed in healthy individuals. 

Signs and symptoms of deficiency Oral and throat swelling, stomatitis, cheilosis, sore throat, eye itching and redness, skin problems, hair loss, hyperemia, liver degeneration, nervous system degeneration, reproductive issues, deficiency of other vitamins 
Signs and symptoms of toxicity None reported  

Laboratory Testing

Assessment of Status

Riboflavin and Metabolites in Erythrocytes, Plasma, or Whole Blood

Direct measurement of riboflavin and its metabolites (FAD and FMN) can be made in erythrocytes, plasma, or whole blood.  All of these measurements except for FAD concentration in plasma are considered adequate indicators of B2 status.  FAD measurements in plasma are affected by inflammation; therefore, testing for erythrocyte FAD concentration is recommended in critically ill patients. 

Erythrocyte Glutathione Reductase Activity Coefficient

The erythrocyte glutathione reductase activity coefficient is an indirect but sensitive measure of riboflavin status.  Erythrocyte glutathione reductase activity is measured as the ratio of erythrocyte glutathione reductase in freshly lysed erythrocytes without and with stimulation with exogenous FAD.   Thresholds for diagnosing deficiency have not been firmly established,  however, and variation between methods may lead to differences in results.  This assay is not useful in patients with glucose-6-phosphate dehydrogenase deficiency. 

Riboflavin in Urine

Fluorometrically measured urine riboflavin excretion reflects recent intake, although concentration may be affected by age, stress, and certain drugs. 

Vitamin B3

Vitamin B3 (niacin) is a collective term for nicotinic acid, nicotinamide, and derivatives with the same biologic activity.  The main active form of niacin is the coenzyme nicotinamide adenine dinucleotide (NAD), which is converted into nicotinamide adenine dinucleotide phosphate (NADP), both of which are required for numerous enzymatic reactions within the body.  Sources of niacin include beans, eggs, meat, milk, fish, nuts, grains, and fortified grain products.  Risk factors for niacin deficiency include malabsorption; inflammatory bowel disease; vitamin B2, B6, or iron deficiency; alcohol dependence; anorexia; cirrhosis of the liver; HIV/AIDS; carcinoid syndrome; and Hartnup disease.  Very high-dose niacin is used as a medication for hyperlipidemia and other conditions. 

Signs and symptoms of deficiency Pellagra (pigmented rash in sun-exposed areas, red tongue, diarrhea, neurologic symptoms) 
Signs and symptoms of toxicity Flushing (redness accompanied by a ”prickly heat” sensation), headaches, rash, dizziness, and blood pressure changes may occur at intakes >30 mg/day; nausea, hepatotoxicity, glucose intolerance, macular edema, and other serious side effects may occur at pharmacologic doses  

Laboratory Testing

Assessment of Status

Niacin in Plasma

Niacin concentration may be measured in plasma, although plasma concentration is not a reliable indicator of niacin status.  

Monitoring

Niacin may lead to adverse side effects when taken in pharmacologic doses; therefore, multiple organizations recommend testing hepatic transaminase, fasting blood glucose or hemoglobin A1c, and uric acid in supplement users before the initiation of therapy, when dosage is increased, and every 6 months after reaching a maintenance dose. 

Vitamin B5

Vitamin B5 (pantothenic acid) is a water-soluble vitamin that is required for the synthesis of coenzyme A (CoA), a critical coenzyme in numerous reactions within the body.  Sources of pantothenic acid include whole grains, some vegetables, meats, fortified cereals and drinks, and other plant- and animal-derived foods.  Although pantothenic acid status is not usually assessed in healthy individuals, it can be measured by a variety of assays in blood, urine, and tissue. 

Signs and symptoms of deficiency Difficult to identify, but may include numbness and burning sensations in the extremities, headache, fatigue, irritability, sleep disturbances, gastrointestinal distress 
Signs and symptoms of toxicity None reported, although diarrhea and gastrointestinal distress may result from large-dose supplement consumption 

Laboratory Testing

Assessment of Status

There are currently no widely used functional tests for pantothenic acid. 

Pantothenic Acid in Serum or Plasma

Serum or plasma contains only the free pantothenic acid form, rather than the active form, and does not accurately reflect pantothenic acid intake or status.   Pantothenic acid serum or plasma testing is primarily used for investigational purposes.

Vitamin B6

Vitamin B6 is a general term for pyridoxine, pyridoxamine, pyridoxal, and their esters. Pyridoxal 5’ phosphate (PLP) and pyridoxamine 5’ phosphate are the active forms and are involved in numerous enzymatic reactions; 4-pyridoxic acid is a catabolic product of vitamin B6 metabolism.   Sources of vitamin B6 include meats, whole grains, fish, vegetables, nuts, noncitrus fruits, and fortified grain products.   Although studies have shown that almost a quarter of people in the U.S. have low plasma PLP concentrations,  clinically relevant vitamin B6 deficiency is rare in otherwise healthy individuals and usually occurs in conjunction with other B vitamin deficiencies. Risk factors for deficiency include obesity, malabsorption (eg, due to celiac disease or Crohn disease), pregnancy, hemodialysis, alcohol dependence, chronic renal insufficiency, and pyridoxine-dependent epilepsy.  Vitamin B6 supplements may be used to treat nausea and vomiting in pregnancy.  Testing for vitamin B6 includes the measurement of PLP or other forms of vitamin B6 in urine, plasma, or whole blood.

Signs and symptoms of deficiency

In adults: dermatitis, glossitis, convulsions, neuropathy, depression, confusion, anemia 

In infants: irritability, hearing sensitivity, seizures 

Signs and symptoms of toxicity Severe sensory neuropathy, dermatologic lesions, dementia 

Laboratory Testing

Assessment of Status

No single marker reflects vitamin B6 status; therefore, use of a combination of tests is recommended.  Thiamine (vitamin B1) testing is frequently ordered in conjunction with B6 testing. Although plasma can be used for B6 testing, B1 tests will not yield accurate results in plasma; thus, whole blood is the preferred specimen when ordering both tests.

Pyridoxal 5’ Phosphate in Plasma or Erythrocytes

PLP concentration in plasma is the most common measure of vitamin B6 status  and may be the best indicator of tissue stores, given that it is thought to reflect the concentration of PLP in liver.  Increases in PLP concentration in plasma occur within 3 days of supplementation. 

4-Pyridoxic Acid in Plasma

4-pyridoxic acid is a product of vitamin B6 metabolism. Increases in 4-pyridoxic acid concentration in plasma occur within 3 days of supplementation.  Reduced concentration may be observed in vitamin B6 deficiency.

Homocysteine in Plasma

Plasma homocysteine is elevated in individuals with suboptimal vitamin B6, B9, or B12 status, or impaired renal function. 

Aspartate Aminotransferase and Alanine Aminotransferase Functional Testing in Erythrocytes

Erythrocyte aspartate aminotransferase and erythrocyte alanine aminotransferase can be activated with PLP to evaluate long-term Bstatus.  However, results may vary based on the method used, and variability is greater for vitamin B6 assays than it is for corresponding assays for vitamins B1 and B2.  For more information on liver enzyme tests, see Liver Disease Evaluation.

PLP is used as an activating reagent in some alanine aminotransferase assays for the evaluation of liver disease.  Thus, if a patient has an abnormal vitamin B6 status, there is the potential for misinterpretation of liver function tests results.

Monitoring

Regular monitoring is recommended for patients who have had bariatric surgery. Testing should also be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

Vitamin B7

Vitamin B7, or biotin, is a cofactor for enzymes involved in metabolism and is also involved in histone modification, cell signaling, and gene regulation.  Sources of biotin include meats, fish, nuts, and some vegetables.  Dietary biotin deficiency is rare but can occur in individuals with biotinidase deficiency.  Other risk factors include malabsorption, pregnancy, breastfeeding, and alcohol dependence. 

Signs and symptoms of deficiency

In adults: rash, hair loss, acidosis, neurologic symptoms, hair and nail problems 

In infants: hypotonia, developmental delay, lethargy 

Signs and symptoms of toxicity None reported, although high biotin intake (eg, use of supplements marketed for hair and nail health) may interfere with certain laboratory assays (eg, hormone tests) 

Laboratory Testing

Assessment of Status

Biotin supplements, many containing more than 500 times the recommended daily intake of biotin, are promoted to improve hair, skin, and nail health.  Such high-dose supplementation may interfere with laboratory tests that use biotin-streptavidin to measure analyte concentrations.  Healthcare providers are advised to ask patients about their use of any dietary supplements, including supplements for hair, skin, and nails, to assist in the assessment of biotin interference as a possible source of error in test results that are not congruent with clinical presentation.  For more information, including a list of tests potentially affected by biotin interference, see the ARUP Laboratories Biotin Interference page.

Biotin in Plasma or Serum

Measurement of biotin in plasma or serum assesses biotin concentration but does not indicate biotin status.  Low biotin concentrations in plasma and serum are not sensitive markers of inadequate biotin intake because they do not decrease substantially with mild biotin deficiency.  

Vitamin B9

Vitamin B9 (folate, folic acid, or folacin) is essential for gene expression and cell division.  Sources of folate include fortified breads, fortified cereals and grain products, fruits, leafy green vegetables, and dried legumes.   Risk factors for folate deficiency and corresponding megaloblastic anemia include malabsorptive disorders (celiac disease, tropical sprue, Crohn disease), alcohol dependence, SLC46A1 (protein-coupled folate transporter) variants, and the 677C>T MTHFR gene variant.    Folate deficiency is usually accompanied by deficiency of multiple other nutrients, especially vitamin B12; folate supplementation is thought to mask the symptoms of vitamin B12 deficiency.  Pregnant women require increased folate intake to reduce the risk of neural tube defects in their infants. 

Signs and symptoms of deficiency Megaloblastic anemia, glossitis, diarrhea, skin and fingernail changes; maternal deficiency leads to fetal open neural tube defects (eg, spina bifida) 
Signs and symptoms of toxicity None confirmed, but may include exacerbation of vitamin B12 deficiency symptoms, increased cancer risk, immune effects, and cognitive consequences 

Laboratory Testing

Assessment of Status

Coexisting iron deficiency or vitamin B12 deficiency may interfere with the diagnosis of folate deficiency, given that supplemental folate may treat the anemia associated with B12 and folate deficiency while allowing progression of neurologic complications of B12 deficiency.  

Folate in Serum or Plasma

Measurement of folate in serum or plasma is the preferred initial test for folate status,  although results may reflect recent dietary intake of folate. Assessment of cobalamin (vitamin B12) and folate status is often performed concurrently because the biochemical pathways for the two vitamins are closely related, and deficiency of either vitamin results in similar clinical features.  Serum folate testing is preferred over erythrocyte folate in cases of vitamin B12 deficiency. 

Folate in Erythrocytes

Erythrocyte folate concentration is a longer-term indicator of folate intake than serum folate.  Because the folate content of red blood cells is fixed during erythropoiesis, erythrocyte folate is indicative of folate status over the preceding 120 days.  

Homocysteine in Plasma

Plasma homocysteine concentration increases in cases of folate deficiency, although it may also be elevated due to vitamin B6 or B12 deficiency or other factors (eg, impaired renal function).   Thus, plasma homocysteine can be used as a nonspecific functional indicator of folate status, particularly in combination with serum or erythrocyte folate. 

Monitoring

Testing for folate status in patients who have had bariatric surgery should be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

Vitamin B12

Vitamin B12, or cobalamin, is the name for several forms of cobalt-containing compounds with vitamin B12 activity.  Cobalamins, specifically the active forms methylcobalamin and 5-deoxyadenosylcobalamin, are essential coenzymes for methyl transfer reactions in the body.  Vitamin B12 is also necessary for proper blood formation, DNA synthesis, and neurologic health.  Sources of vitamin B12 include animal products, dairy products, and fortified products.   Although most people in the U.S. consume more than the recommended amounts of vitamin B12, vitamin B12 deficiency is still a common condition and may lead to megaloblastic anemia.  Risk factors for vitamin B12 deficiency include short bowel syndrome, alcohol dependence, vegan diet, gastrointestinal disorders (eg, celiac disease), older age, pernicious anemia, and low stomach acidity.  

Signs and symptoms of deficiency Megaloblastic anemia, fatigue, weight loss, numbness or tingling of the extremities, balance problems, cognitive symptoms, sore tongue or mouth 
Signs and symptoms of toxicity None reported 

Laboratory Testing

Assessment of Status

Long-term consumption of large amounts of folic acid (folate) may delay the diagnosis of anemia in the case of vitamin B12 deficiency, which may increase the risk of neurologic damage. 

Vitamin B12 in Serum or Plasma

A variety of methods are used to determine the concentration of vitamin B12 in serum or plasma.  Serum or plasma B12 concentration reflects both intake and stores.  However, serum concentrations may be maintained even when tissue stores are depleted; thus, although a low concentration may indicate a long-term abnormality or low intake, an adequate concentration does not necessarily indicate adequate tissue stores.  Concentration in serum or plasma may be abnormally high if the patient has received vitamin B12 injections within the 2 weeks before the test.

Methylmalonic Acid in Serum, Plasma, or Urine

Insufficient vitamin B12 causes methylmalonic acid (MMA) concentration to rise.  Because elevated MMA concentration is tightly correlated with vitamin B12 status, MMA concentration might be a more sensitive, more reliable, and earlier indicator of vitamin B12 deficiency than vitamin B12 plasma concentration.   Furthermore, MMA concentration is not affected by folate deficiency and is therefore more specific than other indirect measures of vitamin B12 status.  MMA concentration is increased in individuals with impaired renal function and in older individuals (>65 years of age) in the absence of B12 deficiency.  

Homocysteine in Plasma

Plasma homocysteine concentration may increase in the case of vitamin B12 deficiency, although it may also be elevated due to vitamin B6 or folate deficiency or other factors (eg, impaired renal function).   Thus, plasma homocysteine can be used as a nonspecific indicator of B12 status, particularly in combination with other tests.

Monitoring

Monitoring for vitamin B12 deficiency should be considered for the following patients:

  • Patients who have had bariatric surgery and who present with signs and symptoms of deficiency, regardless of how long ago the surgery was performed; regular monitoring is also recommended; see the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations
  • Individuals using metformin, particularly those with anemia or peripheral neuropathy 
  • Individuals using proton pump inhibitors for prolonged periods 

Vitamin C

Vitamin C (ascorbic acid), a key antioxidant within the body, is involved in a variety of biosynthetic reactions and plays a role in immunity and iron absorption.   Sources of vitamin C include fruits (especially citrus fruits), vegetables, and fortified grains.   Vitamin C deficiency and toxicity are rare in the U.S. Insufficiency, however, may be present in infants not receiving breast milk or formula and in individuals who smoke, consume a diet with limited food variety, or have certain medical conditions (eg, cancer).   High-dose vitamin C may be provided intravenously for therapeutic purposes in patients with cancer.

Signs and symptoms of deficiency Scurvy (fatigue, connective tissue weakness, capillary fragility, bleeding gums, coiled hairs)  
Signs and symptoms of toxicity Abdominal pain, diarrhea, nausea, and other gastrointestinal upset  ; vitamin C may increase iron overload in patients with hereditary hemochromatosis and may increase risk of nephrolithiasis 

Laboratory Testing

Assessment of Status

There are currently no widely used functional indicators of vitamin C status; direct measurements are used instead.  Vitamin C is light, temperature, and oxidant sensitive, and is unstable in plasma.  Addition of a preservative should be considered,  and samples should be carefully prepared and rapidly frozen to minimize exposure to light and heat.

Vitamin C in Plasma, Serum, or Urine

Vitamin C status is usually measured via high-performance liquid chromatography with electrochemical detection as total ascorbic acid in plasma or serum, although other detection methods can be used.  Measurements in plasma and serum indicate the availability of circulating vitamin C and are considered reliable indicators of intake.   However, concentration of vitamin C in plasma or serum may be extremely high if the patient is receiving intravenous vitamin C for therapeutic purposes. Urine ascorbic acid concentration following a load of vitamin C may be useful in the diagnosis of scurvy. 

Vitamin C in Leukocytes

Ascorbic acid may also be measured in buffy coat or leukocytes.  Vitamin C in leukocytes may reflect the tissue vitamin C concentration more accurately than plasma measurements.  However, the performance of these assays is difficult; thus, they are not widely used. 

Vitamin D

Vitamin D (calciferol) is the collective name for a group of fat-soluble compounds that includes ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D functions as a hormone precursor and is required for calcium absorption, bone metabolism, and regulation of cell development and immune function.  Unlike other vitamins, vitamin D in the body may be derived from the diet or may be synthesized in the skin in response to sun exposure.  The body converts vitamin D into 25-hydroxyvitamin D [25(OH)D], its major circulating form, and 1,25-dihydroxyvitamin D [1,25(OH)2D], its major active form.  Vitamin D testing includes testing for 25-hydroxyvitamin D (the preferred test for nutritional status), as well as measurement of 1,25-dihydroxyvitamin D [25(OH)2D] (discouraged unless the patient has hypercalcemia or decreased kidney function).   For more information about vitamin D testing, see the Vitamin D Testing Test Fact Sheet.

Vitamin E

Vitamin E is a term for the group of antioxidant tocopherols and tocotrienols.  Vitamin E occurs in eight forms, including alpha (α)-tocopherol and gamma (γ)-tocopherol. In addition to its antioxidant activity, vitamin E is involved in immunity, cell signaling, gene regulation, and metabolism.  Sources of vitamin E include seeds and nuts, vegetable oils, leafy green vegetables, and fortified products.  Risk factors for deficiency include fat malabsorption disorders (eg, Crohn disease, cystic fibrosis), and abetalipoproteinemia.  

Signs and symptoms of deficiency Peripheral neuropathy, ataxia, skeletal myopathy, immune problems, pigmented retinopathy 
Signs and symptoms of toxicitya Reduced platelet aggregation and hemorrhagic effects 
aSupplements may interfere with certain medications, including anticoagulants, simvastatin and niacin, and chemotherapy drugs. 

Laboratory Testing

Assessment of Status

Vitamin E in Serum or Plasma

Alpha- and γ-tocopherol are the vitamers most commonly used to assess vitamin E status.  High-performance liquid chromatography is the preferred method for measuring vitamin E in serum or plasma. 

Monitoring

Patients with cystic fibrosis are particularly prone to malabsorption of fat-soluble vitamins, including vitamin E.  Many cystic fibrosis organizations recommend supplementation and careful monitoring. 

Regular monitoring is recommended for patients who have had bariatric surgery. Testing should also be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

Vitamin K

Vitamin K refers to fat-soluble compounds with a 2-methyl-1,4-naphthoquinone structure, including phylloquinone (K1) and menaquinone (K2).  Vitamin K is necessary for the formation of blood clots and bone metabolism, among other functions.  Phylloquinone is found in leafy green vegetables, whereas sources of menaquinone include bacteria (which synthesize menaquinone in the human gut), animal foods, and fermented foods.  Vitamin K deficiency is rare in adults, generally a result of malabsorption, cystic fibrosis, or liver disease, and is only clinically problematic when clotting time is increased.   Newborns, however, may be born without sufficient vitamin K stores, leading to excessive bleeding. The American Academy of Pediatrics recommends that all newborns receive a one-time intramuscular dose of vitamin K.  Laboratory testing for vitamin K is generally not performed except in patients taking anticoagulant medication or with a bleeding disorder. 

Signs and symptoms of deficiency

In adults: increased clotting time, hemorrhage, osteoporosis

In infants: vitamin K deficiency bleeding (hemorrhagic disease of the newborn) 

Signs and symptoms of toxicity None reported  a
aExcess vitamin K may interfere with oral anticoagulants (eg, warfarin).

Laboratory Testing

Assessment of Status

Phylloquinone in Serum or Plasma

Fasting serum or plasma phylloquinone concentration correlates with intake and is considered the best indicator of vitamin K1 status.   However, this test does not assess menaquinone (K2), and patients with low phylloquinone concentration may not exhibit clinical symptoms of vitamin K deficiency. 

Vitamin K Indirect Functional Tests

Vitamin K status is generally determined indirectly by measuring the function of vitamin K-dependent proteins.   Plasma prothrombin time (PT) and the international normalized ratio (INR, an expression of the prothrombin time as a fraction of control time) are the most commonly used tests.  PT and INR increase in the case of vitamin K deficiency, reflecting clinically significant reduced clotting ability. 

Monitoring

Functional vitamin K tests (eg, INR) are commonly used for monitoring in warfarin dosing and in bleeding disorders. For more information, see the Prolonged Clotting Time Evaluation, Hemophilia, and Uncommon Factor Deficiencies ARUP Consult topics.

Patients with cystic fibrosis are particularly prone to malabsorption of fat-soluble vitamins, including vitamin K.  Many cystic fibrosis organizations recommend supplementation and careful monitoring.  If liver disease is present, PT testing is recommended at 2 months after the initiation of supplementation and annually thereafter, or more often if results are abnormal. 

Testing for vitamin K status in patients who have had bariatric surgery should be considered if signs or symptoms of deficiency are present, regardless of how much time has passed since the surgery was performed. See the Gastric Bypass – Bariatric Surgery Postoperative Monitoring ARUP Consult topic for specific recommendations.

ARUP Lab Tests

Vitamin A

Use for nutritional assessment of vitamin A (retinol and retinyl palmitate) in serum or plasma

May be helpful as an indicator of malnutrition, acute and chronic hepatic disease, advanced chronic renal insufficiency, or cystic fibrosis

Assess nephrotic syndrome and protein-losing enteropathy

May be useful as a supplemental test for the assessment of vitamin A status

Use to assess fat malabsorption

Vitamin B1

Use for nutritional assessment of vitamin B1 (thiamine)

Do not use for evaluation of thiamine sufficiency

Refer to Vitamin B1 (Thiamine), Whole Blood (0080388) for nutritional assessment of thiamine

Vitamin B2

Use for nutritional assessment of vitamin B2

Vitamin B3

Assess niacin concentration in plasma

Vitamin B5

Assess pantothenic acid concentration in serum

Vitamin B6

Use for nutritional assessment of vitamin B6

Vitamin B7

Assess biotin concentration in serum

This test is NOT indicated for diagnosing patients with biotinidase deficiency or as follow-up for an abnormal newborn screen for biotinidase deficiency

Use in combination with other tests to confirm or monitor patients with biotinidase deficiency

Vitamin B9

Aids in detection of folate deficiency

Aids in detection of vitamin B12 and folate deficiency in individuals with macrocytic or unexplained anemia, or unexplained neurologic disease

Vitamin B12

Preferred test for evaluating vitamin B12 deficiency

Preferred reflex test for evaluating vitamin B12 deficiency in individuals with macrocytic or unexplained anemia, or unexplained neurologic disease

Reflex pattern: if vitamin B12 is less than 300 pg/mL, then methylmalonic acid, serum will be added

Aids in detection of vitamin B12 deficiency in individuals with macrocytic or unexplained anemia, or unexplained neurologic disease

Use to evaluate vitamin B12 deficiency in individuals with macrocytic or unexplained anemia, or unexplained neurologic disease

Preferred test is Vitamin B12 with Reflex to Methylmalonic Acid, Serum (Vitamin B12 Status) (0055662)

Aids in detection of vitamin B12 and folate deficiency in individuals with macrocytic or unexplained anemia, or unexplained neurologic disease

Vitamin C

Use for nutritional assessment of vitamin C

Vitamin D

Preferred test to diagnose vitamin D insufficiency and monitor response to therapy

Testing is recommended only for patients at risk for vitamin D insufficiency

May be useful to evaluate calcium metabolism in individuals with hypercalcemia or renal failure in addition to Vitamin D, 25-Hydroxy testing

Test is not appropriate for diagnosing vitamin D deficiency or insufficiency

Vitamin E

Use for nutritional assessment of vitamin E (α- and γ-tocopherols)

Vitamin K

Use for nutritional assessment of vitamin K1

Indirect functional tests for vitamin K

Medical Experts

Contributor

Frank

Elizabeth L. Frank, PhD, DABCC
Professor of Clinical Pathology, University of Utah
Medical Director, Analytic Biochemistry, Calculi and Manual Chemistry; Co-Medical Director, Mass Spectrometry, ARUP Laboratories

References

  1. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline - Chapter 4

    Institute of Medicine (US) Standing Committee on the Scientific Evaluation of Dietary Reference Intakes and its Panel on Folate, Other B Vitamins, and Choline. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Chapter 4. Washington (DC): National Academies Press (US); 1998. 

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