Proteins

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

Laboratory Testing

  • Albumin – usual first-line test in evaluating nutritional status
    • Elevated concentrations – dehydration
    • Decreased concentrations are very common
      • Impaired synthesis
      • 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
    • 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
    • Prealbumin used as marker of nutritional status in the following
      • Premature infants
      • Cancer patients
      • Surgical patients
    • Prealbumin is a negative acute phase reactant
      • Due to decreased synthesis, prealbumin serum concentrations fall in these diseases
        • Inflammation
        • Malignancy
        • Cirrhosis of the liver
        • Protein-wasting diseases of the gut or kidney
    • Recommended test for protein measurement in evaluation of nutrition in hospitalized patients
  • 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, including 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 the following
        • Inflammation
        • Malignancy
        • Chronic liver disease
        • Protein loss
    • Elevated fecal clearance of alpha-1-antitrypsin in protein-losing enteropathy
  • Also recommend vitamin/mineral assay testing

Hepatic proteins refer to a group of proteins synthesized in the liver that may be used in the assessment of nutritional status. Hepatic proteins include the following

  • Albumin
  • Prealbumin (transthyretin)
  • Retinol-binding protein (RBP)
  • Transferrin

Etiologies

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
    • Prealbumin has 2-day half-life
      • Short half-life makes it a good indicator for early monitoring
      • Unaffected by hydration status
  • 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

Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

Albumin, Serum or Plasma by Spectrophotometry 0020030
Method: Quantitative Spectrophotometry

Limitations

Albumin may be acutely decreased in sepsis or trauma

Prealbumin, Serum 0050435
Method: Immunoturbidimetry

Limitations

Prealbumin may be acutely decreased in sepsis or trauma

Retinol Binding Protein 0050467
Method: Quantitative Nephelometry

Transferrin, Serum 0050570
Method: Quantitative Immunoturbidimetry

Alpha-1-Antitrypsin Clearance, Quantitative by ELISA, Timed Stool 2011043
Method: Enzyme-Linked Immunosorbent Assay/Quantitative Immunoturbidimetry

Alpha-1-Antitrypsin, Quantitative by ELISA, Random Stool 2011041
Method: Quantitative Enzyme-Linked Immunosorbent Assay

Alpha-1-Antitrypsin 0050001
Method: Quantitative Immunoturbidimetry

General References

Buxbaum JN, Reixach N. Transthyretin: the servant of many masters. Cell Mol Life Sci. 2009; 66(19): 3095-101. PubMed

Danziger J. Importance of low-grade albuminuria. Mayo Clin Proc. 2008; 83(7): 806-12. PubMed

Ellegård LH, Bosaeus IG. Biochemical indices to evaluate nutritional support for malignant disease. Clin Chim Acta. 2008; 390(1-2): 23-7. PubMed

Kmieć Z. Cooperation of liver cells in health and disease. Adv Anat Embryol Cell Biol. 2001; 161: III-XIII, 1-151. PubMed

Pencharz PB. Assessment of protein nutritional status in children. Pediatr Blood Cancer. 2008; 50(2 Suppl): 445-6; discussion 451. PubMed

Perez Valdivieso JRamon, Bes-Rastrollo M, Monedero P, de Irala J, Lavilla FJavier. Impact of prealbumin levels on mortality in patients with acute kidney injury: an observational cohort study. J Ren Nutr. 2008; 18(3): 262-8. PubMed

Suzuki N, Kida K, Suzuki K, Harada T, Akashi YJ. Assessment of transthyretin combined with mini nutritional assessment on admission provides useful prognostic information in patients with acute decompensated heart failure. Int Heart J. 2015; 56(2): 226-33. PubMed

Medical Reviewers

Last Update: December 2015