Hepatic Proteins

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

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
    • 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
      • 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
  • 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

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 Lab Tests

Evaluate production of albumin by liver; assess nutritional status

Assess nephrotic syndrome and protein-losing enteropathy

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

Indicate early malnutrition, acute and chronic hepatitic disease, advanced chronic renal insufficiency, and cystic fibrosis

Assess nephrotic syndrome and protein-losing enteropathy

Aid in differential diagnosis of malnutrition

Monitor iron deficiency anemia

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

Follow-up test when protein-losing enteropathy is suspected

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

Medical Experts

Contributor

Delgado

Julio Delgado, MD, MS
Professor of Clinical Pathology, University of Utah
Chief, Division of Clinical Pathology, University of Utah and ARUP Laboratories
Chief Medical Officer and Director of Laboratories at ARUP Laboratories
Contributor

Genzen

Jonathan R. Genzen, MD, PhD

Associate Professor of Clinical Pathology, University of Utah

Chief Operations Officer, Medical Director of Automated Core Laboratory and Farmington Health Center Clinical Laboratory, at ARUP Laboratories

Contributor

Schlaberg

Robert Schlaberg, MD, MPH
Assistant Professor of Clinical Pathology, University of Utah
Medical Director, Microbial Amplified Detection, Virology, and Fecal Chemistry, and Assistant Medical Director, Virology and Molecular Infectious Disease at ARUP Laboratories

References

Additional Resources