Amylase

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Subject: Amylase

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Definition

  • Amylases are a group of hydrolases that degrade complex carbohydrates into fragments. Amylase is produced by the exocrine pancreas and the salivary glands to aid in the digestion of starch. It is also produced by the small intestine mucosa, ovaries, placenta, liver, and fallopian tubes.

  • Normal range: 5–125 U/L.

Use

  • To diagnose and monitor pancreatitis or other pancreatic diseases

  • In the workup of any intra-abdominal inflammatory event

Interpretation

Increased In

  • Acute pancreatitis (e.g., alcoholic, autoimmune). Urine levels reflect serum changes by a time lag of 6–10 hours.

  • Acute exacerbation of chronic pancreatitis.

  • Drug-induced acute pancreatitis (e.g., aminosalicylic acid, azathioprine, corticosteroids, dexamethasone, ethacrynic acid, ethanol, furosemide, thiazides, mercaptopurine, phenformin, triamcinolone).

  • Drug-induced methodologic interference (e.g., pancreozymin [contains amylase], chloride and fluoride salts [enhance amylase activity], lipemic serum [turbidimetric methods]).

  • Obstruction of pancreatic duct by

    • Stone or carcinoma

      • Drug-induced spasm of the sphincter of Oddi (e.g., opiates, codeine, methyl choline, cholinergics, chlorothiazide) to levels 2–15 times normal

      • Partial obstruction + drug stimulation

    • Biliary tract disease

    • Common bile duct obstruction

    • Acute cholecystitis

  • Complications of pancreatitis (pseudocyst, ascites, abscess).

  • Pancreatic trauma (abdominal injury; following ERCP).

  • Altered GI tract permeability:

    • Ischemic bowel disease or frank perforation

    • Esophageal rupture

    • Perforated or penetrating peptic ulcer

    • Postoperative upper abdominal surgery, especially partial gastrectomy (≤2 times normal in one third of patients)

  • Acute alcohol ingestion or poisoning.

  • Salivary gland disease (mumps, suppurative inflammation, duct obstruction due to calculus, radiation).

  • Malignant tumors (especially pancreas, lung, ovary, esophagus; also breast, colon); usually >25 times upper reference limit, which is rarely seen in pancreatitis.

  • Advanced renal insufficiency; often increased even without pancreatitis.

  • Macroamylasemia.

  • Others, such as chronic liver disease (e.g., cirrhosis; ≤2 times normal), burns, pregnancy (including ruptured tubal pregnancy), ovarian cyst, diabetic ketoacidosis, recent thoracic surgery, myoglobinuria, presence of myeloma proteins, some cases of intracranial bleeding (unknown mechanism), splenic rupture, and dissecting aneurysm.

  • It has been suggested that a level >1,000 Somogyi units is usually due to surgically correctable lesions (most frequently stones in biliary tree), the pancreas being negative or showing only edema; but 200–500 U is usually associated with pancreatic lesions that are not surgically correctable (e.g., hemorrhagic pancreatitis, necrosis of pancreas).

  • Increased serum amylase with low urine amylase may be seen in renal insufficiency and macroamylasemia. Serum amylase ≤4 times normal in renal disease only when creatinine clearance is <50 mL/minute due to pancreatic or salivary isoamylase; but rarely more than four times normal in the absence of acute pancreatitis.

Decreased In

  • Extensive marked destruction of the pancreas (e.g., acute fulminant pancreatitis, advanced chronic pancreatitis, advanced cystic fibrosis). Decreased levels are clinically significant only in occasional cases of fulminant pancreatitis.

  • Severe liver damage (e.g., hepatitis, poisoning, toxemia of pregnancy, severe thyrotoxicosis, severe burns).

  • 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.

 
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