LAP is a proteolytic enzyme widely distributed in bacteria, plants, and animals with high activity in the duodenum, kidney, and liver.
Normal range: 1.0 " “3.3 U/mL.
Use
As a marker of hepatic and pancreatic carcinoma.
As a marker of early tubular (renal) injury in diabetes and as an indicator of SLE activity.
Parallels serum ALP except that
LAP is usually normal in the presence of bone disease or malabsorption syndrome.
LAP is a more sensitive indicator of choledocholithiasis and of liver metastases in anicteric patients.
When serum LAP is increased, urine LAP is almost always increased, but when urine LAP is increased, serum LAP may have already returned to normal.
Interpretation
Increased In
Obstructive, space-occupying, or infiltrative lesions of the liver
SLE, in correlation with disease activity
Various neoplasms (even without liver metastases) (e.g., breast, endometrium, and germ cell tumors)
Preeclampsia, between 33 and 39 weeks of pregnancy
Limitations
Testing serum LAP is generally not as sensitive or as convenient as testing other liver enzymes to detect some liver problems. ALT, AST, ALP, LDH, and GGT are more commonly measured for the same purpose. Unlike other liver enzymes, LAP can be measured in the urine.
Elevated LAP activity in serum usually indicates diseases of liver and bile ducts, and this elevation is less affected by damage of liver parenchyma than by active participation of biliary tract in the process.