Type of test Blood; urine

 Normal findings

Blood

Adult: 60-120 Somogyi units/dL or 30-220 units/L (SI units)

Values may be slightly increased during normal pregnancy and in the elderly. Newborn: 6-65 units/L

 Urine (24-hour)

Up to 5000 Somogyi units/24 hr or 6.5-48.1 units/hr (SI units)

 Possible critical values

Blood: More than three times the upper limit of normal (depending on the method)

Test explanation and related physiology

Serum amylase is an easily and rapidly performed test that is commonly used to diagnose and monitor the treatment of pancreatitis or obstruction of the pancreatic duct flow (as a result of pancreatic carcinoma). Blood vessels draining the free peritoneum and absorbing the lymph pick up the excess amylase. An abnormal rise in the serum level of amylase occurs within 12 hours of the onset of disease. Because amylase is rapidly cleared by the kidneys, serum levels return to normal 48 to 72 hours after the initial insult. Persistent pancreatitis, duct obstruction, or pancreatic duct leak will cause persistent elevated amylase levels.

Although serum amylase is a sensitive test for pancreatic dis orders, it is not specific. Other nonpancreatic diseases can cause elevated amylase levels in the serum. For example, in a bowel perforation, intraluminal amylase leaks into the free peritoneum and is picked up by the peritoneal blood vessels. Also, a penetrating peptic ulcer into the pancreas will cause elevated amylase levels. Duodenal obstruction can be associated with less significant elevations in amylase. Because salivary glands contain amylase, elevations can be expected in patients with parotiditis (mumps). Amylase isoenzyme testing can differentiate pancreatic from salivary hyperamylasemia.

 Urine amylase levels rise after the blood levels. Several days after the onset of the disease process, serum amylase levels may be normal, but urine amylase levels are significantly elevated. Urine amylase is particularly useful in detecting pancreatitis late in the disease course.

As with serum amylase, urine amylase is sensitive but not specific for pancreatic disorders. A comparison of the renal clearance ratio of amylase with creatinine provides more specific diagnostic information than either the urine amylase level or the serum amylase level alone. When the amylase/creatinine clearance ratio is 5% or more, the diagnosis of pancreatitis can be made with certainty.

Interfering factors

 • Serum lipemia may falsely decrease amylase levels.

* IV dextrose solutions can cause a false-negative result.

* Drugs that may cause increased serum amylase levels include aminosalicylic acid, aspirin, azathioprine, corticosteroids, dexamethasone, ethyl alcohol, glucocorticoids, iodine- containing contrast media, loop diuretics, methyldopa, narcotic analgesics, oral contraceptives, and prednisone.

* Drugs that may cause decreased levels include citrates, glucose, and oxalates. Procedure and patient care

 • See inside front cover for Routine Blood Testing.

• Fasting: no

 • Blood tube commonly used: red

 • See inside front cover for Routine Urine Testing.

 Abnormal findings

Increased levels

- Acute or chronic relapsing pancreatitis

- Penetrating or perforated peptic ulcer

- Necrotic or perforated bowel

-  Acute cholecystitis

- Parotiditis (mumps)

- Ectopic pregnancy

- Pulmonary infarction

-  Diabetic ketoacidosis

- Duodenal obstruction

- Osteogenic sarcoma

- Cryoglobulinemia

- Rheumatoid diseases