Hepatic proteins are a group of proteins synthesized in the liver that may be used in the assessment of nutritional status. Hepatic proteins include albumin, prealbumin (transthyretin), retinol-binding protein (RBP), and transferrin.
Diagnosis
Indications for Testing
- Known disease that would cause compromised nutritional status (eg, cancer, malabsorption)
- Failure to thrive in children
Laboratory Testing
- Albumin – usual first-line test in evaluating nutritional status
- Elevated concentrations – dehydration
- Decreased concentrations are very common
- Impaired synthesis
- Primary (eg, liver disease)
- Secondary (eg, low protein intake)
- Increased catabolism – result of tissue damage and inflammation
- Reduced absorption of amino acids – malabsorption or malnutrition
- Excessive protein loss in urine, feces, or skin – glomerulonephritis, nephrotic syndrome, protein-losing enteropathy
- Altered distribution that sequesters large amounts of albumin in extravascular compartment
- Nephrotic syndrome
- Congestive heart failure
- Impaired synthesis
- Albumin measurement in urine may aid in early detection of renal involvement in chronic diseases
- Prealbumin – may be a better early screening test due to short half-life
- Used as marker of nutritional status in
- Premature infants
- Cancer patients
- Surgical patients
- Negative acute phase reactant – concentrations fall in the following diseases due to decreased synthesis
- Recommended test for protein measurement in evaluation of nutrition in hospitalized patients
- Used as marker of nutritional status in
- Retinol-binding protein (RBP), transferrin, and fecal alpha-1-antitrypsin – less widely used as screening tests
- Decreased concentrations of RBP – cystic fibrosis, liver disease
- Elevated concentrations of transferrin
- Malnutrition
- Acute inflammation
- Infection
- Renal disorders
- Red blood cell disorders (eg, iron deficiency)
- High concentrations can occur in pregnancy and during estrogen administration
- Decreased concentrations of transferrin
- Transferrin is a negative acute phase reactant
- Low concentrations occur in
- Inflammation
- Malignancy
- Chronic liver disease
- Protein loss
- Elevated fecal clearance of alpha-1-antitrypsin in protein-losing enteropathy
- Vitamin/mineral assay testing also recommended
Background
Etiologies
- Starvation
- Chronic disease
- HIV
- Malignancy
- Chronic liver disease
- Chronic kidney disease
- Chronic obstructive pulmonary disease (COPD)
- Anorexia
- Malabsorption
- Critical illness or trauma
Pathophysiology
- Albumin
- Function – carrier protein for minerals, fatty acids, vitamins, and hormones
- Most abundant protein in human plasma – 55-65% of total protein content
- Most commonly monitored protein – long half-life (20 days) makes it a relatively insensitive marker
- Prealbumin (transthyretin)
- Function – carrier protein for thyroid hormone
- 2-day half-life
- Short half-life makes it a good indicator for early monitoring
- Unaffected by hydration status
- Retinol-binding protein (RBP)
- Function – responsible for binding and transporting retinol (vitamin A)
- Short half-life (11 hours) makes it an excellent indicator of early malnutrition
- Transferrin
- Function – carrier protein for iron
- Presence of transferrin in serum and other body fluids aids in differential diagnosis
- Alpha-1-antitrypsin (fecal)
- Function – protease inhibitor
Clinical Presentation
- Constitutional – weight loss, muscle wasting, fatigue, failure to thrive (children)
- Skin changes from vitamin deficiencies may occur in chronic loss
- Extremes – kwashiorkor manifesting with ascites, edema
ARUP Laboratory Tests
Evaluate production of albumin by liver; assess nutritional status
Assess nephrotic syndrome and protein-losing enteropathy
Quantitative Spectrophotometry
Assess nutritional status in premature infants, in cancer patients, and surgical patients
Recommended protein measurement to evaluate nutritional status in hospitalized patients
Assess nephrotic syndrome and protein-losing enteropathy
Immunoturbidimetry
Indicate early malnutrition, acute and chronic hepatitic disease, advanced chronic renal insufficiency, and cystic fibrosis
Assess nephrotic syndrome and protein-losing enteropathy
Quantitative Nephelometry
Aid in differential diagnosis of malnutrition
Monitor iron deficiency anemia
Quantitative Immunoturbidimetry
Follow-up test when protein-losing enteropathy is suspected
If serum or plasma specimen is not submitted in conjunction with timed stool collection, order alpha-1-antitrypsin (AAT) random stool test
Enzyme-Linked Immunosorbent Assay/Quantitative Immunoturbidimetry
Follow-up test when protein-losing enteropathy is suspected
Quantitative Enzyme-Linked Immunosorbent Assay
Determine AAT enzyme plasma concentration for the initial evaluation of AAT deficiency
Acutely ill AAT-deficient patients may have falsely normal AAT concentrations
Calculations for the AAT fecal test require that this test also be ordered
Quantitative Immunoturbidimetry
Medical Experts
Delgado

Genzen

Schlaberg
