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1302 Alanine Aminotransferase (ALT) Albumin

Alanine Aminotransferase (ALT)
VetBooks.ir Definition Lab Artifacts

Increases from muscle injury are uncommon,
Enzyme in hepatocyte cytoplasm diabetes mellitus), or systemic infections. Increase: hemolysis (in vivo or artifactual).
but may occur with muscular dystrophy.
Synonym(s) Specimen Collection and Handling
Glutamic pyruvate transaminase (GPT)— Next Diagnostic Steps to Consider Serum (red top tube). Heparinized or EDTA
obsolete if Levels Are High anticoagulated plasma may be substituted.
If values > 3 times the upper limit of refer-
Physiology ence interval or persistently increased, assess Relative Cost: $
ALT is released from the cytoplasm following history for exposure to hepatotoxins (including
hepatocyte cell membrane injury. Low concen- medications) or support for secondary causes Pearls
trations in erythrocytes or skeletal muscle may (e.g., gastrointestinal disease, endocrinopathy). • Increased ALT indicates hepatocyte damage
cause minor (usually clinically insignificant) If none, assess hepatic structure (e.g., abdominal but is not a test of hepatic function, nor does
increases in hemolytic diseases or with muscle radiographs, ultrasound) and function (e.g., it predict reversibility of hepatocyte injury.
injury, respectively. pre- and postprandial serum bile acids). • Minimally increased ALT may indicate
Consider biopsy if values remain increased or serious disease processes or relatively
Reference Interval if hepatic abnormalities are identified with the benign conditions; correlating values with
Reference interval is variable among laboratories aforementioned testing. other clinical and laboratory findings and
and dependent upon analyzers/methodologies. monitoring trends are essential for properly
Causes of Abnormally Low Levels interpreting high ALT values.
Causes of Abnormally High Levels Low values are of no clinical significance.
Hepatocellular injury from any cause. May be AUTHOR: Mary Leissinger, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
primary (e.g., hepatitis, lipidosis, neoplasia, Drug Effects
blunt trauma, hepatotoxins) or secondary Many drugs can induce hepatocellular injury,
to gastrointestinal disease (e.g., pancreatitis, including azathioprine, glucocorticoids, car-
inflammatory bowel disease), hypoxia (e.g., profen, phenobarbital, methimazole, megestrol
congestive heart failure, hypotension, severe acetate, itra-/ketoconazole, lomustine (CCNU)
anemia), endocrinopathy (e.g., hyperthyroidism, and tetracycline.

Albumin

Definition Causes of Abnormally Low Levels in conjunction with hematocrit, total protein,
Albumin is the predominant protein in • Decreased production. Marked decrease in globulins, liver values, and markers of renal
peripheral blood. liver function (>80%), portosystemic shunt, function. If evidence of significant inflam-
acute phase response (inflammation), severe mation, consider acute-phase response. If a
Physiology malnutrition/starvation, cachectic state, cause is not determined, consider additional
Albumin is synthesized by the liver. It is the hypoadrenocorticism. diagnostics to assess GI/urinary protein loss and
major contributor to plasma oncotic pressure • Increased loss. May be loss of only albumin liver function (e.g., fecal flotation, urinalysis,
and also functions as a transport protein for (selective) or all proteins (nonselective). urine protein/creatinine ratio, bile acids, serum
ions, bilirubin, thyroxine, numerous drugs, and ○ Selective. Protein-losing glomerulopathy. folate/cobalamin).
other compounds. Albumin lost while globulins maintained. See p. 1239.
○ Nonselective. Protein-losing enteropathy,
Reference Interval hemorrhage, severe exudative dermatopathy/ Drug Effects
Dogs and cats: 2.8-4.2 g/dL (28 to 42 g/L) burns. Both albumin and globulins lost, Increases in albumin are reported in dogs
but if concurrent inflammation present, administered glucocorticoids in experimental
Causes of Abnormally High Levels globulins may not fall below reference studies. Effect may be mediated by increased
Dehydration or volume contraction second- range. glucocorticoid production and/or free water loss
ary to fluid loss is most common. In dogs, • Sequestration. Third space loss into body from corticosteroid-induced polyuria.
hyperalbuminemia has rarely been reported cavities with effusion or vasculitis.
with hepatocellular carcinoma. Glucocorticoid • Dilution. Iatrogenic fluid overload, patho- Lab Artifacts
administration may cause a mild increase in logic fluid retention (e.g., congestive heart • Hemolysis and/or lipemia may cause
albumin concentration. failure, cirrhosis, syndrome of inappropriate hyperalbuminemia, but impact is analyzer/
antidiuretic hormone secretion) method dependent.
Next Diagnostic Steps to Consider • Use of reagents for human testing. Bromo-
if Levels Are High Next Diagnostic Steps to Consider cresol purple used in human medicine does
Assess hydration status. If normal, recheck if Levels Are Low not reliably bind to albumin molecules in
results. Review the history/medical record for Review history and physical exam with respect other species, resulting in artifactually low
glucocorticoid usage. to intestinal, renal, and liver function. Assess albumin measurements.

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