Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (694 page)

   Methodologic interference by drugs (e.g., citrate and oxalate decrease activity by binding calcium ions)

   Normal: 1–5%

   Macroamylasemia: <1%; very useful for this diagnosis

   Acute pancreatitis: >5%; use is presently discouraged for this diagnosis

   Amylase-to-creatinine clearance ratio = (urine amylase/serum amylase) (serum creatinine/urine creatinine) × 100

Normal In

   Relapsing chronic pancreatitis

   Patients with hypertriglyceridemia (technical interference with test)

   Frequently normal in acute alcoholic pancreatitis

   Limitations

   Composed of pancreatic and salivary types of isoamylases distinguished by various methodologies; nonpancreatic etiologies are almost always salivary; both types may be increased in renal insufficiency.

   An elevation of total serum α-amylase does not specifically indicate a pancreatic disorder, since the enzyme is produced by the salivary glands, mucosa of the small intestine, ovaries, placenta, liver, and the lining of the fallopian tubes.

   Pancreatic amylase results may be elevated in patients with macroamylase. This elevated pancreatic amylase is not diagnostic for pancreatitis. By utilizing serum lipase and urinary amylase values, the presence or absence of macroamylase may be determined.

AMYLASE, URINE (AMYLASE/CREATININE CLEARANCE RATIO [ALCR])

   Definition