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Ammonia Amylase 1305

Ammonia
VetBooks.ir Definition Next Diagnostic Steps to Consider

ship on dry ice so sample does not thaw in
Nitrogenous product of protein catabolism if Levels Are High or freeze (−20°C) within 3 hours. If frozen,
Review history, examination, complete blood shipment. Arterial samples preferred but not
Synonyms count, serum biochemistry panel, and abdomi- essential. Concurrent submission of a sample
Though commonly referred to as ammonia nal imaging results for signs of hepatobiliary from a healthy control animal for comparison is
(NH 3), the dominant form in blood is disease and portal circulation abnormalities. generally recommended or required to exclude
+
ammonium (NH 4 ). Exclude physiologic or artifactual causes. artifact as a cause of abnormal values.
Physiology Drug Effects Relative Cost: $$
Ammonia is produced in the gastrointestinal Decrease: antibiotics that affect gastrointestinal
tract by bacterial metabolism of dietary amino flora, lactulose, Lactobacillus acidophilus culture, Pearls
acids and carried via the portal circulation to enema. • Given the many preanalytic factors that
the liver, where most is converted to urea in may impact ammonia measurement,
the urea cycle. Lab Artifacts always contact the laboratory or be aware
• Increase: delay in harvesting plasma (>30 of laboratory sample handling policy before
Reference Interval minutes), inappropriate submission to submission to ensure best results.
Variable among laboratories but generally less laboratory (see specimen collection and • Ammonia is superior to bile acids for
than 90-100 mcg/dL (53-59 mcmol/L) in dogs handling), or sample hemolysis. Interference assessing hepatic function if cholestasis is
and cats. from icterus/lipemia is method/analyzer present.
dependent.
Causes of Abnormally High Levels • Decrease: inappropriately filled or stoppered AUTHOR: Mary Leissinger, DVM, MS, DACVP
• Artifact: inappropriate sample handling and tube (loss of ammonia gas) EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
sample condition (common)
• Physiologic: high protein meal or extreme Specimen Collection and Handling
exercise Twelve-hour fasting specimen preferred. Collect
• Pathophysiologic: abnormalities in hepatic heparinized whole blood (green top tube),
portal blood flow (acquired or congenital separate plasma from cells immediately, store
shunts), decreased liver function, urea cycle on ice. Some laboratories may accept EDTA
abnormalities (rare), cobalamin deficiency (purple top tube) plasma or serum. Must test

Laboratory Tests

Amylase

Definition acute or chronic kidney disease, hypovolemia) fluoride oxalate tubes for sample collection
Enzyme that hydrolyzes complex carbohydrates. often cause mild hyperamylasemia. Pancreatic results in decreased amylase results (amylase
Measured in serum or plasma as a marker for neoplasia is an uncommon cause. activity is calcium dependent).
acute pancreatitis, though it lacks specificity
and sensitivity for this condition. Next Diagnostic Steps to Consider Specimen Collection and Handling
if Levels Are High Serum (red top tube) or heparinized plasma
Physiology If history, clinical signs, and other initial (green top tube) may be used. Fasting patient
Amylase is a cytosolic enzyme produced by diagnostics are compatible with pancreatitis, to minimize risk of lipemia is recommended.
multiple tissue types, most notably pancreatic abdominal imaging, pancreas-specific lipase Separate serum or plasma from cells if shipping
acinar epithelium, intestine, and liver. Accord- immunoreactivity, or DGGR lipase measure- to a laboratory. Stable at 2°C - 8°C for 1 month.
ingly, damage to pancreatic acinar epithelium ment may be considered.
can result in leakage of amylase to the blood. Relative Cost: $
Renal excretion/inactivation and hepatic clear- Important Interspecies Differences
ance are both involved in clearing amylase from Amylase is of little value in assessing cats for Pearls
the blood. pancreatitis. Salivary amylase (present in some • Mild hyperamylasemia has very poor specific-
species) is not found in dogs or cats. ity for diagnosis of pancreatitis. The greater
Reference Interval the magnitude of hyperamylasemia, the
Varies by laboratory, often < 1600 U/L Drug Effects more likely acute pancreatitis or pancreatic
Administration of dexamethasone or prednisone neoplasia becomes.
Causes of Abnormally High Levels may decrease amylase activity level. • Pancreatitis can be present even if amylase
Acute pancreatitis (and the resultant pancreatic is within reference interval.
acinar epithelial damage) is the most common Lab Artifacts
cause of moderate to markedly increased values. Marked lipemia, hemolysis, or icterus may cause AUTHOR: Angela Royal, DVM, MS, DACVP
EDITOR: Lois Roth-Johnson, DVM, PhD, DACVP
Decreases in glomerular filtration rate (GFR; erroneous results. Use of EDTA, citrate, or
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