Amylase is a calcium dependent enzyme which hydrolyzes complex carbohydrates at alpha 1,4-linkages
to form maltose and glucose. Amylase is filtered by renal tubules and resorbed (inactivated) by tubular
epithelium. Active enzyme does not appear in urine. Small amounts of amylase are taken up by Kupffer cells in the liver. In healthy dogs, 14% of amylase is bound to globulins. Because of this polymerization, canine amylase has variable (high) molecular weights and is not normally filtered by the kidney. In dogs with renal disease, this polymerized (macroamylase) amylase is found in higher concentration (from 5-62% of total amylase activity) and contributes to the hyperamylasemia seen in these disorders.
There are 4 different isoenzymes of amylase in the dog: isoenzyme 3 is found in the pancreas (>50%), whereas isoenzyme 4 is found in all tissues.
There are several different assays for amylase:
1) Saccharogenic - This methodology measures the rate of appearance
of reducing sugars (glucose, maltose). This methodology is invalid
in the dog as dog serum contains maltase. Maltase is additive to the
activity of amylase and will produce increased numbers of reducing
2) Amyloclastic - This method measures the hydrolysis of starch and
the rate of its disappearance. Valid for dogs and other domestic species.
Lipemic samples may show an inhibition of enzyme activity which can
be overcome by dilution.
- Turbidometric: Size of the starch substrate decreases with
hydrolysis which reduces light scatter.
- Chromogenic substrates: These use dyes bound to synthetic
starch substrates, with the dye being released (and measured) once
the substrate is hydrolyzed. Chromogenic substrate techniques are
the current clinical amylase assay.
Causes of hyperamylasemia
- Pancreas: Found in zymogen granules. The pancreas has higher concentrations of amylase than other tissues.
- Intestine: Duodenum, ileum
- Ovary and testes
- Salivary gland: Salivary amylase is found in high concentration in pigs, resultilng in high reference intervals for amylase in this species. Dogs lack salivary amylase.
- Acute pancreatitis: The increase and decrease of serum amylase
tends to parallel that of lipase. Values should be at least double
reference values to be considered significant, and often may reach
7-10 times normal. Amylase values peak at 12-48 hours and are normal
within 8-14 days after a bout of pancreatitis in dogs. It is rare
to observe increased amylase in cats with pancreatitis. Note that
amylase concentrations are often higher in ascitic fluid than in blood
in animals with pancreatitis (or intestinal disease).
- Chronic renal insufficiency: As discussed above, the increase
in amylase is due to macroamylase formation (polymerization with globulins).
- Decreased GFR: This can cause increased amylase (up to 2-3
x normal) in the absence of significant pancreatic disease. If an
azotemic patient has amylase values greater than 2 to 3 times the
reference values, pancreatitis should receive consideration as a diagnosis.
Amylase is variably increased in cats with disorders associated with
renal azotemia. However, this mechanism may not apply to dogs. Dogs
do not typically excrete amylase via the kidney. The increased amylase
seen in dogs with conditions associated with decreased GFR (pre-renal,
renal, post-renal azotemia) may be due to macroamylase formation.
- Intestinal disease/obstruction: Moderate elevations in amylase