Serum Amylase test

Serum amylase test is a blood test that measures the level of amylase in your body. 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.

Amylase is an essential enzyme that plays a crucial role in the digestion of carbohydrates. It breaks down complex carbohydrates, such as starch and glycogen, into simpler sugars, such as glucose and maltose. These simpler sugars can then be absorbed into the bloodstream and utilized by cells for energy production

The amylase test is used to:

• Diagnose acute or chronic pancreatitis
• Monitor the course of pancreatitis
• Help determine the cause of abdominal pain
• Evaluate the effectiveness of treatment for pancreatitis.

Normal reference range of serum amylase ⁴ –

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

Instruction to patients before collecting amylase sample

fasting not required . patient should not drink alcohol for 24 hours before the test.

Sample Serum

Container:

• Red-top tube (no additive)
• Gel-barrier tube (serum separator tube, SST)
• Green-top tube (lithium heparin)

Collection:

Separate serum or plasma from cells within 45 minutes of collection.

Please note that hemolysis and the use of anticoagulants other than lithium heparin can cause interference with the amylase test.

Increased levels of serum amylase are seen in

Acute or chronic relapsing pancreatitis- Serum levels of amylase and lipase more than three times the normal value usually indicate acute inflammation of the pancreas

Non pancreatic causes of raised amylase

Penetrating or perforated peptic ulcer

Necrotic or perforated bowel

Acute cholecystitis

Parotiditis (mumps)

Ectopic pregnancy

Pulmonary infarction

Diabetic ketoacidosis

Duodenal obstruction

Osteogenic sarcoma

Cryoglobulinemia

Limitations

Factors that can affect serum amylase levels:

• Serum lipemia: High levels of fats (lipids) in the blood, known as lipemia, can interfere with the measurement of amylase levels, potentially leading to falsely decreased amylase readings.
• IV dextrose solutions: Intravenous administration of dextrose solutions, a type of sugar solution used for hydration, can also cause false-negative amylase results.
• Drugs that increase amylase levels: Certain medications can elevate serum amylase levels, including:
  • Aminosalicylic acid
  • Aspirin
  • Azathioprine
  • Corticosteroids
  • Dexamethasone
  • Ethyl alcohol (ethanol)
  • Glucocorticoids
  • Iodine-containing contrast media
  • Loop diuretics
  • Methyldopa
  • Narcotic analgesics
  • Oral contraceptives
  • Prednisone
• Because salivary glands contain amylase, elevations can be expected in patients with parotiditis (mumps).Amylase isoenzyme testing can differentiate pancreatic from salivary hyperamylasemia.
• Macroamylasemia is a condition characterized by the presence of elevated serum amylase levels with a large molecular size.The formation of these complexes may lead to reduced clearance of amylase by the kidneys, resulting in prolonged circulation of the larger molecular forms in the bloodstream. Despite the elevated levels of amylase, individuals with macroamylasemia may not exhibit symptoms related to pancreatic dysfunction.
• Causes of macroamylasaemia are liver disease, diabetes mellitus ,autoimmune disorders, malignancy ,malabsorption.
• In cases of macroamylasemia, the elevated serum amylase is typically not associated with an increase in serum lipase levels. Additionally, urinary amylase levels are usually normal in macroamylasemia, while in acute pancreatitis, urinary amylase levels may be elevated.

Urine amylase level

Serum amylase serves as a crucial diagnostic marker for acute pancreatitis However, its short half-life of around 10 to 12 hours poses limitations in its effectiveness, particularly for detecting mild pancreatitis or in patients presenting late.

Due to its rapid clearance from the bloodstream, serum amylase levels often return to normal within 3 to 5 days after the onset of pancreatitis. This rapid decline can lead to inconsistencies in diagnosis, especially in cases with milder symptoms or those presenting later in the disease course.

To address this limitation, urine amylase has emerged as a valuable complementary diagnostic tool. Urine amylase, excreted by the kidneys, exhibits a prolonged half-life, typically remaining elevated for 7 to 14 days after serum amylase levels have normalized. This extended elevation makes urine amylase more effective in detecting late-stage pancreatitis and cases with milder symptoms.

Urine amylase also helps to differentiate between pancreatitis and macroamylasemia ,as macroamylase complex are not filtered due to their large size.

References

1. Fischbach FT, Dunning MB III, eds. Manual of Laboratory and Diagnostic Tests. 8th ed. Philadelphia: Lippincott Williams and Wilkins; 2009.
2. Henry JB. Clinical Diagnosis and Management by Laboratory Methods.
3. SAXON EI, HINKLEY WC, VOGEL WC, ZIEVE L. Comparative value of serum and urinary amylase in the diagnosis of acute pancreatitis. AMA Arch Intern Med. 1957 Apr;99(4):607-21. doi: 10.1001/archinte.1957.00260040107011. PMID: 13410166.
4. Pagana KD, Pagana TJ, Pagana TN. Mosby’s Diagnostic and Laboratory Test Reference. 14th ed. St. Louis, MO: Elsevier; 2019. 56.