Leucine aminopeptidase (LAP) is a proteolytic enzyme which is present in human blood serum. Its serum concentration is usually elevated in disease of the hepatobiliary system. Banks et al.1 have described the clinical value of measuring LAP activity. More recently, Rutenburg et al.2 reported high LAP levels in 26 (90%) of 29 infants with icterus due to biliary atresia or extra-hepatic obstruction. In contrast, normal LAP activity was observed in 7 (88%) of 8 infants with neonatal hepatitis, 1 to 14 weeks after onset of jaundice.
The use of the LAP test for the differential diagnosis of jaundice has highlighted the need for knowledge of the pattern of activity of this enzyme in various diseases of the liver. The consideration of viral hepatitis in the differentiation of "medical" from "surgical" jaundice is of particular importance. This report of serum LAP activity in infectious hepatitis is a by-product of