Introduction
- Lipase is an important digestive enzyme that hydrolyzes triglycerides into fatty acids and glycerol.
- It is produced mainly by the pancreas and acts in the intestine for fat digestion.
- Small amounts are also secreted by salivary glands, gastric mucosa, intestinal mucosa, and lungs.
- Serum lipase estimation is mainly used for diagnosis of pancreatic disorders.
- Lipase is more specific than amylase for pancreatic injury.
- In acute pancreatitis, serum lipase rises significantly and remains elevated for a longer period than amylase.
- Therefore serum lipase is an important laboratory marker in abdominal emergencies.
Principle
- Serum lipase estimation is based on enzymatic colorimetric method.
- The substrate used is 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6-methylresorufin) ester.
- Pancreatic lipase cleaves this substrate and releases methylresorufin.
- Methylresorufin produces color in alkaline medium.
- The rate of color formation is directly proportional to lipase activity in the sample.
- Absorbance is measured kinetically at 580 nm.
Reaction
Lipase substrate → Dicarboxylic acid ester → Methylresorufin
Specimen
Sample Type
- Serum is preferred specimen
- Heparin plasma can also be used
Precautions
- Use non-hemolyzed sample
- Fresh specimen preferred
- Avoid contaminated sample
Stability
- 7 days at 20–25°C
- 7 days at 4–8°C
- 1 year at −20°C
Reagents
Reagent 1 (R1)
- Good’s buffer pH 8.0
- Taurodeoxycholate
- Deoxycholate
- Calcium ions
- Colipase
Reagent 2 (R2)
- Tartrate buffer pH 4.0
- Lipase color substrate
Reagent Preparation
- Reagents are liquid and ready to use
Materials Required
- Test tubes
- Micropipette
- Pipette tips
- Semi-auto analyzer / spectrophotometer
- Cuvette
- Timer
- Lipase reagent kit
Procedure
| Components | Test |
|---|---|
| Reagent 1 | 1000 µL |
| Sample | 20 µL |
First Step
- Mix properly
- Incubate at 37°C for 5 minutes
Then Add
| Components | Test |
|---|---|
| Reagent 2 | 250 µL |
Second Step
- Mix properly
- Read absorbance kinetically
Reading
- Measure at 580 nm
- Record change in absorbance per minute (ΔA/min)
Calculation
Formula
Lipase activity (U/L) = ΔA/min × factor
Unit Conversion
U/L × 0.017 = µkat/L
Normal Reference Values
| Sample | Normal Value |
|---|---|
| Serum | ≤ 60 U/L |
Clinical Significance
Increased Serum Lipase Seen In
- Acute pancreatitis
- Chronic pancreatitis
- Pancreatic duct obstruction
- Pancreatic injury
Acute Pancreatitis
- Serum lipase rises within 4–8 hours after onset of abdominal pain
- Peak occurs at 24 hours
- Remains elevated for 8–14 days
Diagnostic Importance
- More specific than serum amylase for pancreatic disease
- Important marker of pancreatic injury
- Useful in diagnosis of acute abdomen
