Lipase Test – Principle, Procedure, Results, Uses

A lipase test is a laboratory diagnostic test which is done to measure the level of lipase enzyme in the blood. Lipase is a digestive enzyme which is mainly produced by pancreas and it helps in digestion of fats. It is the process in which dietary triglycerides are broken down into fatty acids and glycerol so that absorption can occur in intestine. Normally a small amount of lipase is present in blood but when pancreas is damaged or inflamed the level of this enzyme increases in circulation.

It is the preferred test for detection of pancreatic disorders especially acute pancreatitis. This is because lipase shows higher sensitivity and specificity when compared with amylase. In conditions where pancreatic acinar cells are injured the enzyme is released in large quantity into bloodstream and this rise can be detected by the test. Thus the test is considered important in early diagnosis of pancreatic inflammation.

For performing lipase test blood sample is collected from a vein usually after fasting of 8 to 12 hours. Fasting is required because dietary fats can interfere in result and cause turbidity. In laboratory the serum is analysed by colorimetric or turbidimetric methods. In this step lipase acts on a specific substrate and the rate of colour formation is measured which is directly proportional to lipase activity.

The result of lipase test is expressed in units per liter (U/L) and normal range varies with laboratory. In acute pancreatitis the lipase level rises within few hours reaches peak around 24 hours and remains elevated for several days. Very high level usually more than three times normal value is considered diagnostic. Low level of lipase may indicate chronic pancreatic damage such as chronic pancreatitis or cystic fibrosis.

Objectives of Lipase Test

• It is done for diagnosis of acute pancreatitis where serum lipase level is increased more than normal range.
• It is used for evaluation of abdominal symptoms such as severe abdominal pain nausea vomiting fever and loss of appetite to find pancreatic involvement.
• It helps in diagnosis of other pancreatic disorders such as chronic pancreatitis pancreatic carcinoma pancreatic cysts or pseudocysts and pancreatic trauma.
• It is used for assessment of biliary tract disorders including gallstone obstruction common bile duct obstruction and sphincter of Oddi dysfunction.
• It is carried out for monitoring the effectiveness of treatment in pancreatic diseases although lipase level do not always correlate with severity.
• It is useful for identification of pancreatic insufficiency where very low lipase level indicate severe pancreatic cell damage such as in late chronic pancreatitis or cystic fibrosis.
• It helps in differentiation of pancreatic inflammation from other acute abdominal conditions like appendicitis bowel obstruction perforated ulcer or cholecystitis.
• It is also used as an indicator in metabolic and renal conditions where altered lipase level is associated with diabetes metabolic syndrome and chronic kidney disease progression.

Principle of Lipase Test

The principle of lipase test is based on the enzymatic activity of lipase which is mainly synthesised by pancreatic acinar cells. It is the enzyme responsible for digestion of dietary fats. In this process lipase hydrolyses glycerol esters of long chain fatty acids (triglycerides) into free fatty acids and partial glycerides. For proper catalytic activity during the test the presence of bile salts and a protein cofactor called colipase is required. Colipase helps in anchoring the enzyme at lipid–water interface and thus ensures specificity of reaction.

In earlier methods the principle was based on titrimetric and turbidimetric reactions. In titrimetric method serum is incubated with triglyceride substrate such as olive oil. Lipase releases fatty acids which increases acidity of medium and this is measured by titration with sodium hydroxide. In turbidimetric method a stable emulsion of triglycerides produces turbidity. As lipase breaks down fat particles the solution becomes clearer and decrease in light scattering is measured which is directly proportional to lipase activity.

In modern laboratories colorimetric method is commonly used. In this method lipase hydrolyses a synthetic substrate to form monoglyceride and fatty acid. The monoglyceride is further converted to glycerol which undergoes a series of enzymatic reactions producing hydrogen peroxide. This hydrogen peroxide reacts with chromogens in presence of peroxidase to form a coloured compound. The rate of colour development is measured and it is directly related to the concentration of lipase present in the blood sample.

Requirements of Lipase Test

• Patient should be kept fasting for 8 to 12 hours before collection and only water is allowed during this period.
• Drugs history should be reviewed as some medications such as opioids oral contraceptive pills thiazide diuretics and cholinergic drugs may alter lipase level.
• Heavy physical activity or vigorous exercise should be avoided before sample collection to prevent non-specific enzyme release.
• Blood sample is collected by venipuncture usually from vein of arm.
• Serum gel tube (SST) or plain red top tube is preferred for sample collection and lithium heparin tube may also be used in some laboratories.
• Minimum sample volume required is about 0.5 to 1.0 mL of blood although smaller volume may be accepted.
• The collected blood sample should be centrifuged within two hours to separate serum from cellular components.
• Separated serum is stable for several days at room temperature or under refrigeration and can be frozen for long term storage.
• Hemolysed samples should be rejected as release of intracellular contents interfere with test reaction.
• Lipemic samples may interfere with optical reading and may require dilution or special processing.
• Tubes with glycerol lubricated stoppers should not be used as it may give falsely increased lipase value.

Procedure of Lipase Test

1. Patient is advised to remain fasting for 8 to 12 hours before test and only water is allowed.
2. History of drugs is checked and some medicines affecting lipase level may be stopped as advised by doctor.
3. A suitable vein is selected usually from arm or antecubital region and skin is cleaned with antiseptic.
4. Blood is collected by venipuncture using sterile needle.
5. The blood sample is collected in serum gel tube or plain red top tube and lithium heparin tube may also be used.
6. After collection needle is removed and pressure is applied at puncture site.
7. The collected blood sample is allowed to clot and then centrifuged within two hours to separate serum.
8. If sample is lipemic further centrifugation or dilution is done to remove interference.
9. A measured quantity of patient serum is mixed with lipase reagent containing specific substrate and activators.
10. Lipase present in serum hydrolyses the substrate producing fatty acids and other products.
11. These products take part in further reactions forming a coloured compound.
12. The intensity of colour formed is measured by automated analyser at specific wavelength.
13. The rate of colour development is proportional to lipase activity and result is expressed in U/L.

Result of Lipase Test

Normal value

• Result is expressed in units per litre (U/L).
• Normal adult serum lipase level is usually within 0 to 160 U/L.
• In adults below 60 years normal range is about 10 to 140 U/L.
• In adults above 60 years normal value ranges between 24 to 151 U/L.
• Normal value in children varies with age and growth and may show wide range.

Increased lipase level

• Lipase level raised more than three times the upper normal limit indicates acute pancreatitis.
• Increased value is seen in pancreatic disorders such as pancreatic cancer pancreatic duct obstruction and pancreatic cyst or pseudocyst.
• Raised lipase level may occur in abdominal conditions like acute cholecystitis gallstones bowel obstruction peptic ulcer appendicitis and celiac disease.
• High lipase level is observed in renal failure due to decreased clearance of enzyme.
• Increased value may be seen in diabetic ketoacidosis.
• Some drugs like opioids oral contraceptive pills thiazide diuretics and cholinergic drugs can increase lipase level.

Decreased lipase level

• Persistently low lipase level indicates chronic pancreatic damage.
• Low value is seen in chronic pancreatitis due to fibrosis and loss of enzyme producing cells.
• Decreased lipase level is observed in cystic fibrosis with pancreatic insufficiency.
• Low level may be associated with metabolic disorders such as obesity metabolic syndrome and diabetes mellitus.

Time relation of lipase level

• Lipase level starts rising within 4 to 8 hours after pancreatic injury.
• Peak level is reached within about 24 hours.
• Lipase remains elevated for 8 to 14 days and hence useful for late diagnosis.

Organisms Showing Lipase Test Result

Lipase positive organisms

• Staphylococcus aureus
• Staphylococcus epidermidis
• Pseudomonas aeruginosa
• Serratia marcescens
• Bacillus subtilis
• Burkholderia cepacia
• Candida albicans
• Candida tropicalis
• Aspergillus niger
• Rhizopus species

Lipase negative organisms

• Escherichia coli
• Klebsiella pneumoniae
• Proteus mirabilis
• Salmonella species
• Shigella species
• Enterococcus species
• Streptococcus species

Uses of Lipase Test

• It is used for diagnosis of acute pancreatitis and is more specific than amylase.
• It is used to monitor the effectiveness of treatment in pancreatic diseases.
• It helps in diagnosis of chronic pancreatitis and permanent pancreatic damage.
• It is useful in evaluation of biliary tract diseases such as acute cholecystitis gallstones cholangitis and bile duct obstruction.
• It helps in assessment of sphincter of Oddi dysfunction.
• It is used for detection of gastrointestinal conditions like bowel obstruction intestinal infarction perforated peptic ulcer appendicitis and peritonitis.
• It is used in diagnosis of pancreatic tumours pancreatic cancer and pancreatic cyst or pseudocyst.
• It helps in assessment of renal failure and chronic kidney disease due to reduced enzyme clearance.
• Low lipase level is used as a marker for metabolic disorders such as obesity metabolic syndrome and diabetes mellitus.
• It is used in evaluation of chronic diseases like cystic fibrosis celiac disease Crohn’s disease and inflammatory bowel disease.
• It may be useful in conditions such as diabetic ketoacidosis salivary gland inflammation and alcohol related disorders.

Advantages of Lipase Test

• It is more specific for diagnosis of acute pancreatitis as lipase is mainly secreted by pancreas.
• It shows higher sensitivity than amylase in acute pancreatitis cases.
• Lipase level remains elevated for longer duration which helps in late diagnosis.
• It is useful in alcoholic pancreatitis where amylase level may be normal.
• Lipase test is reliable even in patients with high triglyceride level.
• It has longer half life in serum which makes interpretation easier.
• The test is simple rapid and easy to perform in routine laboratories.
• It is cost effective and avoids need of doing both amylase and lipase together.

Limitations of Lipase Test

• Lipase level does not correlate with severity or prognosis of acute pancreatitis.
• Elevated lipase level may be seen in non pancreatic conditions causing false positive result.
• Renal failure can lead to increased lipase level due to reduced clearance.
• Certain drugs like opioids may cause falsely raised lipase level without pancreatic disease.
• Hemolysed blood sample interferes with reaction and affects accuracy of result.
• Lipemic samples with very high triglycerides may give inaccurate readings.
• The test cannot determine exact cause of pancreatic inflammation.
• Rarely macrolipasemia may cause persistently high lipase level without clinical disease.
• Very early testing may miss diagnosis before lipase level rises.
• Diagnostic cut off value may vary and is not uniform in all patients.