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Serum Leucine Aminopeptidase Test – Indications, Procedures

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 6 min read

The leucine aminopeptidase (LAP) test is a rapid test for the detection of enzyme leucine aminopeptidase. Leucine- β- napthalamide impregnated disk serves as a substrate for the detection of leucine aminopeptidase. Serum leucine aminopeptidase determination was found to be a useful screening procedure for hepatobiliary disease in jaundiced and unjaundiced patients. Values under 1,000 units are of no help in the differential diagnosis of jaundice but values above 1,000 units are highly indicative of biliary obstruction. Leucine Aminopeptidase (LAP) test is used to identify catalase-negative gram-positive cocci. Specifically, it differentiates Aerococcus and Leuconostoc from Streptococcus, Enterococcus, Lactococcus, and Pediococcus. The LAP disk is a rapid test for the detection of the enzyme leucine aminopeptidase.

The leucine aminopeptidase test measures how much of this enzyme is in your blood.

Your urine can also be checked for this substance.

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

The health care provider may tell you to temporarily stop taking certain medicines that can affect the test. Drugs that can increase albumin levels include estrogen and progesterone.

Do not stop taking any of your medicines without talking to your provider first.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

Leucine aminopeptidase is a type of protein called an enzyme . This enzyme is normally found in cells of the liver and small intestine.

Your provider may order this test to check if your liver is damaged. Too much leucine aminopeptidase is released into your blood when you have a liver tumor or damage to your liver cells.

This test is not done very often. Other tests, such as gamma-glutamyl transpeptidase , are as accurate and easier to get.

Normal Results

Normal range is:

  • Male: 80 to 200 U/mL
  • Female: 75 to 185 U/mL

Normal value ranges may vary slightly. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal result may be a sign of:

  • Bile flow from the liver is blocked ( cholestasis )
  • Cirrhosis
  • Hepatitis
  • Liver cancer
  • Liver ischemia (reduced blood flow to the liver)
  • Liver necrosis (death of liver tissue)
  • Liver tumor
  • Use of drugs that are toxic to the liver

Risks

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

FAQ

What is leucine aminopeptidase test for?

  • Leucine Aminopeptidase (LAP) test is used to identify catalase-negative gram-positive cocci. Specifically, it differentiates Aerococcus and Leuconostoc from Streptococcus, Enterococcus, Lactococcus, and Pediococcus. The LAP disk is a rapid test for the detection of the enzyme leucine aminopeptidase.

What is serum leucine aminopeptidase?

  • Serum leucine aminopeptidase determination was found to be a useful screening procedure for hepatobiliary disease in jaundiced and unjaundiced patients. Values under 1,000 units are of no help in the differential diagnosis of jaundice but values above 1,000 units are highly indicative of biliary obstruction.

How do you test for leucine?

  • The leucine aminopeptidase (LAP) test measures how much of this enzyme is in your blood. Your urine can also be checked for LAP. Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand.

What reaction is leucine aminopeptidase involved in?

  • A leucine aminopeptidase primarily hydrolyzes amino acid leucine from the N-terminus end of proteins and is involved in free amino acid regulation, which makes it a potential therapeutic target against neglected tropical diseases including leishmaniasis.

Where is aminopeptidase active?

  • Aminopeptidases catalyze the cleavage of amino acids from the amino terminus of protein or peptide substrates. They are widely distributed throughout the animal and plant kingdoms and are found in many subcellular organelles, in cytoplasm, and as membrane components.

Is leucine aminopeptidase an Exopeptidase?

  • Leucine aminopeptidase (LAP) is an exopeptidase that catalyzes the hydrolysis of amino acid residues from the amino terminus of polypeptide chains.

Is aminopeptidase a brush border enzyme?

  • (3.4. 11.7) and III (amino-oligopeptidase, E.C. 3.4. 11.2) are known brush border enzymes.

Where is leucine amino acid found?

Leucine is a branched-chain amino acid (BCAA) — just like valine and isoleucine — and is important for repairing and building muscle. In fact, getting enough leucine may prevent muscle wasting among older adults.
  • Canned navy beans.
  • Cottage cheese.
  • Sesame seeds.
  • Pumpkin seeds.
  • Eggs.
  • Hemp seeds.
  • Lentils.
  • Spirulina.

Is aminopeptidase a protease?

  • Aminopeptidases (EC 3.4. 11.) are an important subset of proteases that hydrolyze peptide bonds at the N-terminus of proteins and peptides (11).

What are aminopeptidase and carboxypeptidase?

  • Aminopeptidase hydrolyses the peptide bond of the amino acid at the amino-terminal of a protein or peptide, releasing a free amino acid. Carboxypeptidase hydrolyses the peptide bond of the amino acid at the carboxyl-terminal of a protein or peptide, again releasing a free amino acid.

Where is Enteropeptidase located?

  • Enteropeptidase is a type II transmembrane serine protease (TTSP) localized to the brush border of the duodenal and jejunal mucosa and synthesized as a zymogen, proenteropeptidase, which requires activation by duodenal or trypsin.

What happens if you lack leucine?

  • Persistently low leucine levels can result in decreased appetite, poor feeding, lethargy, poor growth, weight loss, skin rashes, hair loss, and desquamation. With MSUD, deficiency of isoleucine and valine also may occur and result in symptoms similar to those of leucine deficiency.

What protein has the highest leucine content?

  • High-leucine foods include chicken, beef, pork, fish (tuna), tofu, canned beans, milk, cheese, squash seeds, and eggs. The recommended daily intake for leucine is 39mg per kilogram of body weight, or 17.7mg per pound.

How much leucine is too much?

  • Effect on B-Vitamins: Excess dosage of over 30 grams daily of Leucine has shown adverse effects on Vitamin B6 and Vitamin B3. Excess Leucine inhibits the body’s ability to produce these vitamins and later on, it leads to deficiency diseases.

How much leucine is safe?

  • The recommended daily intake (RDI) for leucine is 17.7 milligrams per pound of your body weight. So a person weighing 180 pounds should get around 3,186 milligrams, or 3.186 grams, of leucine per day.

What is the difference between leucine and L-leucine?

  • L-leucine is the L isomer of leucine amino acid. Leucine is an amino acid that is useful in the biosynthesis of proteins. The key difference between L-leucine and leucine is that L-leucine is the L isomer of the leucine amino acid, whereas leucine is an amino acid that is useful in the biosynthesis of proteins.

What are the side effects of leucine?

  • Very high doses of leucine may cause low blood sugar (hypoglycemia). It may also cause pellagra. Symptoms of this can include skin lesions, hair loss, and gastrointestinal problems. People who are pregnant or breastfeeding shouldn’t use leucine supplements.

Is leucine good for skin?

  • Thanks to this ability, Leucine is an ingredient being used in anti-aging skincare products. It is thought to help regenerate aging skin and reduce fine lines and sagging skin; it is said to create firmer, more supple skin and increase elasticity by repairing aging skin tissue. Leucine also aids in wound healing.

How can I get leucine naturally?

Foods with Leucine
  • Salmon. Get your amino acids from salmon, and you’ll also get omega-3 fatty acids.
  • Chickpeas. These nutritional superstars contain 7g of protein and 6g of fiber in just half a cup, and they are high in iron, too.
  • Brown Rice. Try brown rice instead of white.
  • Eggs.
  • Soybeans.
  • Nuts.
  • Beef.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

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Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.