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Amylase
(Pancreatic & Salivary α-Amylase – Digestive Enzyme)
Synonyms
- Amylase
- α-Amylase
- Pancreatic amylase (P-AMY)
- Salivary amylase (S-AMY)
- Diastase (older term)
- EC 3.2.1.1
Units of Measurement
nkat/L, µkat/L, nmol/(s•L), µmol/(s•L), U/L, IU/L, µmol/(min•L), µmol/(h•L), µmol/(h•mL)
Description
Amylase is an enzyme that catalyzes the hydrolysis of starch and glycogen into smaller sugars.
In humans, amylase originates mainly from:
- Pancreas (40–45%)
- Salivary glands (55–60%)
Serum and urine amylase tests are used in evaluating:
- Acute pancreatitis
- Pancreatic injury
- Salivary gland disorders
- Obstruction of pancreatic duct
- Macroamylasemia
Physiological Role
Amylase converts complex carbohydrates → maltose + dextrins.
Two main isoenzymes:
1. Pancreatic Amylase (P-type)
- Secreted into duodenum
- Rises early in pancreatic inflammation
2. Salivary Amylase (S-type)
- Initiates carbohydrate digestion in the mouth
- Elevated in salivary gland disorders, stress
Clinical Significance
Elevated Amylase
1. Acute Pancreatitis
- Rises within 3–6 hours
- Peaks at 24–30 hours
- Returns to normal in 3–5 days
- Often 3× upper limit of normal (ULN)
2. Chronic Pancreatitis (during acute attacks)
3. Pancreatic Duct Obstruction
- Gallstones
- Tumors
- Sphincter of Oddi dysfunction
4. Non-Pancreatic Causes
- Mumps, parotitis
- Alcohol intoxication
- Renal failure (↓ clearance)
- Intestinal obstruction / infarction
- Ruptured ectopic pregnancy
- Burns / trauma
- Acidosis (DKA)
5. Macroamylasemia
- Amylase bound to IgA/IgG → high serum amylase but low urine amylase
- Benign condition
Low Amylase
Less common, seen in:
- Chronic pancreatitis (damaged acinar cells)
- Pancreatic cancer
- Cystic fibrosis
- Extensive pancreatic necrosis
Reference Intervals
(Tietz 8E + IFCC + Mayo Clinic)
Ranges vary by lab and assay method.
Serum Amylase (Adult)
- 30 – 110 U/L
SI unit: 0.50 – 1.83 µkat/L
(1 U/L = 16.67 nkat/L)
Serum Pancreatic Isoamylase (P-AMY)
- 13 – 53 U/L
Urine Amylase
- 2 – 34 U/h (method-dependent)
Pancreatitis Diagnostic Notes
- Amylase <3× ULN does not rule out pancreatitis.
- Lipase is more specific and stays elevated longer.
- Amylase may be normal in late presenters.
Unit Meanings
| Unit | Meaning |
| nkat/L | nanokatal per liter |
| µkat/L | microkatal per liter |
| nmol/(s•L) | nanomole per second per liter |
| µmol/(s•L) | micromole per second per liter |
| U/L or IU/L | enzyme units per liter |
| µmol/(min•L) | micromole per minute per liter |
| µmol/(h•L) | micromole per hour per liter |
| µmol/(h•mL) | micromole per hour per milliliter |
Time conversions
- µmol/(min•L) × 60 = µmol/(h•L)
- µmol/(h•L) ÷ 1000 = µmol/(h•mL)
Differentiating Isoenzymes
Isoenzyme electrophoresis may help distinguish:
| Condition | P-AMY | S-AMY |
| Acute pancreatitis | ↑↑ | Slight ↑ |
| Parotitis | Normal | ↑↑ |
| Macroamylasemia | ↑ (serum) | Normal |
| Renal failure | ↑↑ | ↑ |
Analytical Notes
- Preferred sample: serum or plasma
- Hemolysis—minimal effect
- Serum amylase may be falsely high in lipemic samples
- Lipase is preferred for diagnosing pancreatitis
Clinical Pearls
- Amylase rises and falls faster than lipase-useful for early diagnosis.
- Normal amylase does not exclude acute pancreatitis.
- In renal failure, amylase can rise to 2–3× normal without pancreatic disease.
- Persistent mild elevation with normal lipase → consider macroamylasemia.
- P-AMY/S-AMY ratio helps distinguish pancreatic vs salivary origin.
Interesting Fact
Amylase was one of the first enzymes discovered in human physiology (1831). Historically, “diastase” was the term used long before the enzyme classification system was introduced.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Enzyme Section (Amylase & Lipase).
- IFCC Enzyme Standardization Guidelines.
- Mayo Clinic Laboratories - Amylase Testing.
- ARUP Consult - Pancreatic Enzyme Disorders.
- ACG / AGA Guidelines - Acute Pancreatitis.
- NIH / MedlinePlus - Amylase Overview.