LeucineAminopeptidase

Leucine Aminopeptidase (LAP) is a proteolytic enzyme that hydrolyzes amino acids (especially leucine) from the N-terminal end of peptides.
It is mainly present in:

• Liver (bile canalicular membrane)
• Biliary epithelium
• Placenta
• Intestine

Clinically, it is used as a marker of hepatobiliary disease.

1️⃣ Obstructive (Cholestatic) Liver Disease – Most Important

LAP is markedly elevated in:

• Obstructive jaundice
• Intrahepatic cholestasis
• Bile duct obstruction
• Carcinoma head of pancreas

🔎 Its rise parallels ALP in biliary obstruction.

👉 Therefore, it is useful in diagnosing cholestasis.

2️⃣ Differentiation from Bone Disease

Unlike ALP:

LAP is not elevated in bone diseases.

Condition ALP LAP
Liver disease ↑ ↑
Bone disease ↑ Normal

👉 Helps confirm that raised ALP is of hepatic origin, not bone.

3️⃣ Pregnancy

• LAP is increased during normal pregnancy
• Due to placental production

Hence, pregnancy must be considered while interpreting results.

4️⃣ Hepatocellular Disease

Moderate elevation seen in:

• Hepatitis
• Cirrhosis
• Fatty liver

But levels are more markedly raised in cholestasis.

5️⃣ Limited Use Today

• Largely replaced by GGT and 5′-nucleotidase
• Still historically important in liver function testing

Normal Reference Range

Approximately 15–60 IU/L
(May vary by laboratory)