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Amylase Enzyme Test

An enzyme that is synthesized primarily in the pancreas and salivary glands, amylase (alpha-amylase or AML) helps digest starch and glycogen in the mouth, stomach, and intestine. In cases of suspected acute pancreatic disease, measurement of serum or urine AML the most important laboratory test.

Purpose

• To diagnose acute pancreatitis.
• To distinguish between acute pancreatitis and other causes of abdominal pain that require immediate surgery.
• To evaluate possible pancreatic injury caused by abdominal trauma or surgery

Patient preparation

• Explain to the patient that this test is used to assess pancreatic function.
• Inform him that he needn't fast before the test but must abstain from alcohol.
• Tell him that this test requires a blood sample. Explain who will perform the venipuncture and when.
• Inform the patient that he may experience transient discomfort from the needle puncture and the tourniquet but that collecting the sample takes less than 3 minutes.
• Withhold drugs that may elevate AML levels. They include aspirin, asparaginase, azathioprine, corti costeroids, cyproheptadine, narcotic analgesics, oral contraceptives, rifampin, sulfasalazine, and thiazide or loop diuretics. If these drugs must be continued, note this on the laboratory slip

Procedure and posttest care

• Perform a venipuncture, and collect the sample in a 7-ml red-top tube.
• If a hematoma develops at the venipuncture site, apply warm soaks.
• Resume administration of drugs discontinued before the test.

Precautions

• If the patient has severe abdominal pain, draw the sample before diagnostic or therapeutic intervention. For accurate results, it's important to obtain an early sample.
• Handle the sample gently to prevent hemolysis.

Reference values

Normal serum amylase levels range from 25 to 160 U/L. (More than 20 methods of measuring serum AML exist, with different ranges of normal values. Test values cannot always be converted to a standard measurement.)

Abnormal findings

After the onset of acute pancreatitis, AML levels begin to rise within 2 hours, peak within 12 to 48 hours, and return to normal within 3 to 4 days. Determination of urine levels should follow normal serum AML results to rule out pancreatitis. Moderate serum elevations may accompany obstruction of the common bile duct, pancreatic duct, or ampulla of Vater; pancreatic injury from a perforated peptic ulcer; pancreatic cancer; and acute salivary gland disease. Impaired kidney function may increase serum levels.

Levels may be slightly elevated in a patient who is asymptomatic or responding unusually to therapy. An AML fractionation test is used to determine the source of the AML and the need for additional tests.

Decreased levels can occur in chronic pancreatitis, pancreatic cancer, cirrhosis, hepatitis, and eclampsia.

Interfering factors

• Hemolysis due to rough handling of the sample.
• Ingestion of ethyl alcohol (possible false-high).
• Aminosalicylic acid, asparaginase, azathioprine, corticosteroids, cyproheptadine, narcotic analgesics, oral contraceptives, pentazocine, rifampin, secretin, sulfasalazine, and thiazide or loop diuretics (possible false-high).
• Recent peripancreatic surgery, perforated ulcer or intestine, abscess, spasm of the sphincter of Oddi or, rarely, macroamylasernia (possible false-high).
• High blood glucose levels associated with diabetes or administration of I.V. glucose solutions (possible decrease).