Leucine aminopeptidase - serum

Alternative names
Serum leucine aminopeptidase

This is a blood test that measures the amount of the enzyme leucine aminopeptidase (LAP).

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test
The health care provider may advise you to discontinue drugs that can affect the test (see “Special considerations”).

For infants and children:
The preparation you can provide for this test depends on your child’s age and previous experiences. For specific information regarding how you can prepare your child, see the following topics:

  • infant test or procedure preparation (birth to 1 year)  
  • toddler test or procedure preparation (1 to 3 years)  
  • preschooler test or procedure preparation (3 to 6 years)  
  • schoolage test or procedure preparation (6 to 12 years)  
  • adolescent test or procedure preparation (12 to 18 years)

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

LAP is an enzyme normally found in liver cells (hepatocytes). It is is also released into the blood after damage to liver cells, such as from drugs or infection (for example, hepatitis). Measurement of LAP in blood may serve as an indicator of liver damage.

LAP can also be released into blood by tumors that arise in the liver, so it may also serve as a tumor marker or indicator.Other enzymes, such as ALT, AST, ALP, LDH, and GGT, are more commonly measured for the same purpose.

Testing serum LAP is generally not as sensitive or as convenient as testing other liver enzymes to detect some liver problems. Unlike other liver enzymes, LAP can be measured in the urine (see LAP - urine).

Normal Values

  • male: 80 to 200 U/ml  
  • female: 75 to 185 U/ml

Note: U/ml = units per milliliter

What abnormal results mean

  • cholestasis  
  • cirrhosis  
  • hepatic (liver) ischemia (blood deficiency)  
  • hepatic necrosis (tissue death)  
  • hepatic tumor  
  • hepatitis

What the risks are

  • excessive bleeding  
  • fainting or feeling light-headed  
  • hematoma (blood accumulating under the skin)  
  • infection (a slight risk any time the skin is broken)  
  • multiple punctures to locate veins

Special considerations

Drugs that can affect LAP measurements include estrogens and progesterones.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Johns Hopkins patient information

Last revised: December 4, 2012
by Harutyun Medina, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.