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Proteins

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

Albumin

The 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
Functions – carrier protein for minerals, fatty acids, vitamins and hormones
Albumin measurement in urine may aid early detection of renal involvement in chronic diseases
Elevated concentrations
- Dehydration
Decreased concentrations are very common
- Impaired synthesis
  - Primary (e.g., liver disease)
  - Secondary (e.g., 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
- Altered distribution that sequesters large amounts of albumin in extravascular compartment
  - Nephrotic syndrome
  - Congestive heart failure

Prealbumin (transthyretin)

Prealbumin (PAB) has 2 day half-life versus albumin (21 day half-life)
- Short half-life makes it a good indicator for early monitoring
- Unaffected by hydration status
Function – carrier protein for thyroid hormone
PAB used as marker of nutritional status in:
- Premature infants
- Cancer patients
- Surgical patients
PAB is a negative acute phase reactant
- Due to decreased synthesis, PAB serum concentrations fall in:
  - Inflammation
  - Malignancy
  - Cirrhosis of liver
  - Protein-wasting diseases of gut or kidney
Recommended protein in evaluation of nutrition in hospitalized patients

Retinol binding protein (RBP)

Transferrin

Function – carrier protein for iron
Presence of transferrin in serum and other body fluids aids in differential diagnosis
Elevated concentrations:
- 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
- Transferrin is a negative acute phase reactant
- Low concentrations occur in:
  - Inflammation
  - Malignancy
  - Chronic liver disease
  - Protein loss

Alpha-1-antitrypsin (fecal)

Function – protease inhibitor
- Elevated fecal clearance
  - Protein-losing enteropathy

Test Name and Number	Recommended Use	Limitations
Albumin, Serum or Plasma by Spectrophotometry 0020030 Method: Spectrophotometry	Evaluate production of albumin by liver; assess nutritional status Assess nephrotic syndrome and protein-losing enteropathy	Albumin may be acutely decreased in sepsis, trauma
Prealbumin, Serum 0050435 Method: Immunoturbidimetric	Assess nutritional status in premature infants, in cancer patients and surgical patients Assess nephrotic syndrome and protein-losing enteropathy	Prealbumin may be acutely decreased in sepsis, trauma
Retinol Binding Protein 0050467 Method: Nephelometry	Indicate early malnutrition, acute and chronic hepatitic disease, advanced chronic renal insufficiency and cystic fibrosis Assess nephrotic syndrome and protein-losing enteropathy
Transferrin, Serum 0050570 Method: Immunoturbidimetric	Aid in differential diagnosis of malnutrition Monitor iron deficiency anemia
Alpha-1-Antitrypsin, Feces 0099991 Method: Radial Immunodiffusion	Order as a follow-up test when protein-losing enteropathy is suspected Test serves as a clearance measure; calculations require that serum alpha-1-antitrypsin test also be ordered	Blood in stool or diarrhea may increase clearance

Indications for Ordering