Histochemical studies of adult liver for leucine aminopeptidase (LAP) utilizing the synthetic substrate L-leucyl-β-naphthylamide show intense activity in the bile duct epithelium and a weaker reaction in the parenchymal cells.1,2 We have also observed high activity in the proliferating bile ducts of liver biopsies from 4 infants with biliary atresia. This intense activity in the bile ducts and the observation that LAP is excreted by the liver into the bile appear to explain the high serum LAP activity resulting from extrahepatic or intrahepatic biliary obstruction.1,3 Diagnostically significant elevations of serum LAP have been shown to relate almost exclusively to diseases of the liver, bile ducts, or pancreas.1,3-6
The normal range of enzymatic activity in infants has not been described and the clinical usefulness of serum LAP elevations in infants with hepatobiliary disease has not been assessed. By adult standards, LAP levels have been reported to be normal
RUTENBURG AM, PINEDA EP, GOLDBARG JA, LEVITAN R, GELLIS SS, SILVERBERG M. Serum Leucine Aminopeptidase: Activity in Normal Infants, in Biliary Atresia, and in Other Diseases. Am J Dis Child. 1962;103(1):47–54. doi:10.1001/archpedi.1962.02080020051008
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