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Bariatric surgeries are used increasingly to treat overweight and obese patients who have clinically relevant signs and symptoms. Approximately 252,000 bariatric surgeries were performed in the United States in 2018. These procedures can be successful in reversing many adverse syndromes associated with obesity (including type II diabetes, hypertension, joint pain, obstructive sleep apnea, hyperlipidemia, and coronary artery disease but there are risks and complications to consider, such as the exacerbation of preexisting nutritional deficiencies and the development of new ones. Some deficiencies present soon after surgery, but the late presentation of nutritional deficiencies can contribute to poor outcomes or devastating complications. Bariatric surgeries that use a restrictive technique, such as sleeve gastrectomy (SG), may lead to nutritional deficiencies due to low intake, whereas surgeries that use a combination of restrictive and malabsorptive techniques, such as Roux-en-Y gastric bypass (RYGB), may lead to deficiencies due to either low intake or malabsorption. Therefore, long-term monitoring for nutritional deficiencies is indicated following all types of bariatric surgery.
Quick Answers for Clinicians
Bariatric surgeries can be classified as restrictive or malabsorptive. Restrictive procedures reduce the volume or capacity of the stomach. Malabsorptive procedures reduce the amount of calories absorbed by altering the flow of food. Sleeve gastrectomy (SG) and Roux-en-Y gastric bypass (RYGB) are the most common types of bariatric surgery performed. SG is a restrictive procedure; RYGB is a dual restrictive and malabsorptive procedure. Adjustable gastric binding (AGB) and biliopancreatic diversion with duodenal switch (BPD/DS) are other available options but account for only a small percentage of bariatric surgeries.
Individuals being considered for bariatric surgery should have a preoperative nutritional assessment to identify deficiencies that may predispose them to a higher risk of nutritional deficiencies postsurgery. When possible, these deficiencies should be corrected before surgery. Assessment typically includes vitamin D, calcium, parathyroid hormone (PTH), ferritin, folate (vitamin B9), and vitamin B12 tests, as well as iron studies. , For more information, refer to the Preoperative Assessment section.
The same tests used for preoperative assessment are also used postoperatively. The biochemical and nutritional testing schedule varies depending on the type of surgery. For more information, refer to the Postoperative Monitoring section.
Indications for Testing
Preoperative nutritional assessment is indicated in all individuals being considered for bariatric surgery. A more extensive evaluation is recommended for those undergoing a malabsorptive procedure.
Following surgery, nutritional monitoring should continue for all patients, at regular intervals or as needed, to monitor for nutritional deficiencies.
Laboratory Testing
Preoperative Assessment
Individuals being considered for bariatric surgery should have baseline biochemical and nutritional testing performed to identify deficiencies that may predispose them to a higher risk of deficiencies after surgery; deficiencies should be corrected before surgery when possible. , ,
Key Micronutrient Testing
Current guidelines recommend preprocedural testing for the following micronutrients in all patients , :
- Calcium (including parathyroid hormone [PTH])
- Vitamin D
- Iron (including ferritin)
- Folate (vitamin B9)
- Vitamin B12
Calcium status can be assessed by measuring concentrations of ionized calcium in serum or whole blood, whereas measuring urinary calcium (24-hour concentrations) can identify hypocalciuria. Evaluation of PTH concentrations (alongside 25-hydroxyvitamin D and calcium) is recommended to detect possible hyperparathyroidism. To determine vitamin D status, 25-hydroxyvitamin D (a marker of vitamin D stores in the body) is preferred in the absence of renal disease.
Iron studies include laboratory tests for iron, iron binding capacity, and ferritin. Ferritin is the most sensitive marker for iron deficiency anemia, which is present in up to 47% of patients before bariatric surgery. However, ferritin concentrations may be affected by inflammation. Iron and iron binding capacity testing, although less sensitive than ferritin testing, is useful to verify the accuracy of ferritin results.
Folate (vitamin B9) deficiency has been reported in some patients before bariatric surgery, although the consumption of fortified foods helps reduce its likelihood. A serum or plasma folate test can be used to assess deficiency, followed by a red blood cell (RBC) folate test if initial results are inconclusive. Patients should also be assessed for vitamin B12 deficiency, which may take longer to present due to the body’s ability to maintain large stores of the vitamin. A serum methylmalonic acid (MMA) test is recommended to evaluate vitamin B12 status.
Additional Micronutrient Testing
More extensive nutritional assessment is recommended in patients undergoing malabsorptive procedures, such as RYGB or biliopancreatic diversion with duodenal switch (BPD/DS), and in those suspected of having a preexisting nutrient deficiency. When more extensive screening is indicated, consider testing for the following micronutrients , :
- Vitamin B1 (thiamine diphosphate)
- Vitamin A
- Vitamin E
- Copper
- Zinc
- Selenium
Postoperative Monitoring
Recommendations for postoperative biochemical and nutritional testing are generally based on the bariatric procedure selected. However, postoperative screening for the following micronutrients should be performed in all patients , :
- Calcium
- Vitamin D
- Iron
- Folate (vitamin B9)
- Vitamin B12
Testing for vitamin B1 (thiamine diphosphate) in whole blood may also be considered.
Refer to the following tables for postoperative recommendations specific to SG, RYGB, and BPD/DS procedures.
Notably, recommendations vary for individuals who become pregnant following bariatric surgery; applicable micronutrient testing should be performed during each trimester. ,
| Micronutrient(s) | Recommendation(s) | Testing |
|---|---|---|
| Vitamin A | Assess as needed in patients who report steatorrhea or symptoms of vitamin A deficiency In the presence of vitamin A deficiency, consider testing for deficiencies in other fat-soluble vitamins, iron, and copper | Vitamin A, serum or plasma |
| Vitamin B1 (thiamine) | In the presence of signs, symptoms, or risk factors for thiamine deficiency, assess within 6 mos of surgery and then every 3-6 mos until symptoms subside | Vitamin B1 (thiamine diphosphate), whole blood |
| Folate (vitamin B9) | Assess at 3 mos, 6 mos, and 12 mos after surgery and annually thereafter | Folate, serum |
| Vitamin B12 | Establish a postoperative baseline and assess annually thereafter In patients using medications that increase the risk of B12 deficiency, assess every 3 mos within the first 12 mos of surgery and annually thereafter or as clinically indicated In patients taking higher doses of folate, measure B12 to identify possible deficiency | MMA, serum Total homocysteine (optional) |
| Vitamin D and calcium | Assess at 3 mos, 6 mos, and 12 mos after surgery and annually thereafter In the presence of vitamin D deficiency, consider testing for deficiencies in other fat-soluble vitamins | 25-hydroxyvitamin D, serum Calcium, serum Calcium, 24-hour urinary (as needed; consider if history of renal stones) PTH, intact with calcium (as needed) Bone formation/resorption markers (as needed; refer to the ARUP Consult Osteoporosis topic for more information) |
| Vitamin E | Assess as needed in symptomatic patients In the presence of vitamin E deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin E, serum |
| Vitamin K | Assess as needed in symptomatic patients In the presence of vitamin K deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin K1, serum |
| Copper | Following treatment for copper deficiency, assess every 3 mos after concentrations have returned to normal Consider measuring copper in patients supplementing zinc or in patients with a known vitamin A deficiency | Copper, serum Ceruloplasmin, serum |
| Iron | Assess within the first 3 mos of surgery and then every 3-6 mos until 12 mos postsurgery; assess annually thereafter | Iron panel CBC Total iron binding capacity Ferritin, serum Soluble transferrin receptor (if available) |
| Zinc | Zinc, serum or plasma | |
| Sources: Mechanick, 2020 ; O’Kane, 2020 | ||
| Micronutrient(s) | Recommendation(s) | Testing |
|---|---|---|
| Vitamin A | Assess within the first 12 mos of surgery and annually thereafter, or as needed in patients with symptoms of vitamin A deficiency or protein-calorie malnutrition In the presence of vitamin A deficiency, consider testing for deficiencies in other fat-soluble vitamins, iron, and copper | Vitamin A, serum or plasma |
| Vitamin B1 (thiamine) | In the presence of signs, symptoms, or risk factors for thiamine deficiency, assess within 6 mos of surgery and then every 3-6 mos until symptoms subside | Vitamin B1 (thiamine diphosphate), whole blood |
| Folate (vitamin B9) | Assess at 3 mos, 6 mos, and 12 mos after surgery and annually thereafter | Folate, serum |
| Vitamin B12 | Establish a postoperative baseline and assess annually thereafter In patients using medications that increase the risk of B12 deficiency, assess every 3 mos within the first 12 mos of surgery and annually thereafter or as clinically indicated In patients taking higher doses of folate, measure B12 to identify possible deficiency | MMA, serum Total homocysteine (optional) |
| Vitamin D and calcium | Assess at 3 mos, 6 mos, and 12 mos after surgery and annually thereafter In the presence of vitamin D deficiency, consider testing for deficiencies in other fat-soluble vitamins | 25-hydroxyvitamin D, serum Calcium, serum Calcium, 24-hour urinary (as needed; consider if history of renal stones) PTH, intact with calcium (as needed) Bone formation/resorption markers (as needed; refer to the ARUP Consult Osteoporosis topic for more information) |
| Vitamin E | Assess as needed in symptomatic patients In the presence of vitamin E deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin E, serum |
| Vitamin K | Assess as needed in symptomatic patients In the presence of vitamin K deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin K1, serum |
| Copper | Following treatment for copper deficiency, assess every 3 mos after concentrations have returned to normal Consider measuring copper in patients supplementing zinc or in patients with a known vitamin A deficiency | Copper, serum Ceruloplasmin, serum |
| Iron | Assess within the first 3 mos of surgery and then every 3-6 mos until 12 mos postsurgery; assess annually thereafter Consider testing for other causes of nutritional anemia, including deficiencies in vitamin B12, folate, copper, selenium, or zinc, when iron deficiency has been ruled out | Iron panel CBC Total iron binding capacity Ferritin, serum Soluble transferrin receptor (if available) |
| Selenium | Assess as needed in patients presenting with unexplained anemia or symptoms consistent with selenium deficiency | Selenium, serum |
| Zinc | Zinc, serum or plasma | |
| Sources: Mechanick, 2020 ; O’Kane, 2020 | ||
| Micronutrient(s) | Recommendation(s) | Testing |
|---|---|---|
| Vitamin A | Assess within the first 12 mos of surgery and annually thereafter, or as needed in patients with symptoms of vitamin A deficiency or protein-calorie malnutrition< p=""> > In the presence of vitamin A deficiency, consider testing for deficiencies in other fat-soluble vitamins, iron, and copper | Vitamin A, serum or plasma |
| Vitamin B1 (thiamine) | In the presence of signs, symptoms, or risk factors for thiamine deficiency, assess within 6 mos of surgery and then every 3-6 mos until symptoms subside | Vitamin B1 (thiamine diphosphate), whole blood |
| Folate (vitamin B9) | Assess at 3 mos, 6 mos, and 12 mos after surgery and annually thereafter | Folate, serum |
| Vitamin B12 | Establish a postoperative baseline and assess annually thereafter In patients using medications that increase the risk of B12 deficiency, assess every 3 mos within the first 12 mos of surgery and annually thereafter or as clinically indicated In patients taking higher doses of folate, test B12 to identify possible deficiency | MMA, serum Total homocysteine (optional) |
| Vitamin D and calcium | Assess at 3 mos, 6 mos, and 12 months after surgery and annually thereafter In the presence of vitamin D deficiency, consider testing for deficiencies in other fat-soluble vitamins | 25-hydroxyvitamin D, serum Calcium, serum Calcium, 24-hour urinary (as needed; consider if history of renal stones) PTH, intact with calcium (as needed) Bone formation/resorption markers (as needed; refer to the ARUP Consult Osteoporosis topic for more information) |
| Vitamin E | Assess as needed in symptomatic patients In the presence of vitamin E deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin E, serum |
| Vitamin K | Assess as needed in symptomatic patients In the presence of vitamin K deficiency, consider testing for deficiencies in other fat-soluble vitamins | Vitamin K1, serum |
| Copper | Following treatment for copper deficiency, assess every 3 mos after concentrations have returned to normal Consider measuring copper in patients supplementing zinc or in patients with known vitamin A deficiency | Copper, serum Ceruloplasmin, serum |
| Iron | Assess within the first 3 mos of surgery and then every 3-6 mos until 12 mos postsurgery; assess annually thereafter Consider testing for other causes of nutritional anemia, including deficiencies in vitamin B12, folate, copper, selenium, or zinc, when iron deficiency has been ruled out | Iron panel CBC Total iron binding capacity Ferritin, serum Soluble transferrin receptor (if available) |
| Selenium | Assess as needed in patients presenting with unexplained anemia or symptoms consistent with selenium deficiency | Selenium, serum |
| Zinc | Zinc, serum or plasma | |
| Sources: Mechanick, 2020 ; O’Kane, 2020 | ||
ARUP Laboratory Tests
Ion-Selective Electrode/pH Electrode
Quantitative Immunoturbidimetry
Quantitative Inductively Coupled Plasma-Mass Spectrometry
Quantitative Chemiluminescent Immunoassay
Quantitative Chemiluminescent Immunoassay
Quantitative Chemiluminescent Immunoassay
Quantitative Spectrophotometry
Quantitative Liquid Chromatography-Tandem Mass Spectrometry
Quantitative Electrochemiluminescent Immunoassay (ECLIA)
Quantitative Immunoturbidimetry
Quantitative High Performance Liquid Chromatography (HPLC)
Quantitative High Performance Liquid Chromatography (HPLC)/Liquid Chromatography-Tandem Mass Spectrometry
Quantitative Chemiluminescent Immunoassay
Quantitative Inductively Coupled Plasma-Mass Spectrometry
References
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ASMBS - Estimate of Bariatric Surgery Numbers, 2011-2018
American Society for Metabolic and Bariatric Surgery. Estimate of bariatric surgery numbers, 2011-2020. Published Jun 2022; accessed Jan 2023.
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Mohapatra S, Gangadharan K, Pitchumoni CS. Malnutrition in obesity before and after bariatric surgery. Dis Mon. 2020;66(2):100866.
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Gletsu-Miller N, Wright BN. Mineral malnutrition following bariatric surgery. Adv Nutr. 2013;4(5):506-517.
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Bray GA, Heisel WE, Afshin A, et al. The science of obesity management: an Endocrine Society scientific statement. Endocr Rev. 2018;39(2):79-132.
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ACOS - Bariatric metabolic surgery: Advances continue
Brethauer S, Herron D, Demaria EJ, et al. Bariatric metabolic surgery: advances continue. Bull Am Coll Surg. Published Feb 2019; accessed Jan 2023.
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Mechanick JI, Apovian C, Brethauer S, et al. Clinical practice guidelines for the perioperative nutrition, metabolic, and nonsurgical support of patients undergoing bariatric procedures - 2019 update: cosponsored by American Association of Clinical Endocrinologists/American College of Endocrinology, The Obesity Society, American Society for Metabolic & Bariatric Surgery, Obesity Medicine Association, and American Society of Anesthesiologists. Surg Obes Relat Dis. 2020(16)2:175-247.
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O'Kane M, Parretti HM, Pinkney J, et al. British Obesity and Metabolic Surgery Society guidelines on perioperative and postoperative biochemical monitoring and micronutrient replacement for patients undergoing bariatric surgery-2020 update. Obes Rev. 2020;21(11):e13087.
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Weng TC, Chang CH, Dong YH, et al. Anaemia and related nutrient deficiencies after Roux-en-Y gastric bypass surgery: a systematic review and meta-analysis. BMJ Open. 2015;5(7):e006964.
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Kim J, Nimeri A, Khorgami Z, et al. Metabolic bone changes after bariatric surgery: 2020 update, American Society for Metabolic and Bariatric Surgery Clinical Issues Committee position statement. Surg Obes Relat Dis. 2021;17(1):1-8.
Nutritional assessment and/or postoperative monitoring of patients undergoing bariatric surgery includes the following recommended tests. Refer to the ARUP Laboratory Test Directory for additional nutrient testing options.