Background: Obstructive jaundice is believed to be characterized by abnormalities of alkaline phosphatase (ALP), rather than aspartate transaminase (AST).
Aim: To compare liver function tests (LFTs) in obstructive jaundice due to malignant strictures with those of jaundice due to gallstones.
Methods: LFTs were measured immediately before endoscopic retrograde cholangio-pancreatography (ERCP) in 207 jaundiced patients. Group 1 (n = 69) had malignant strictures, group 2 (n = 97) had common bile duct stone(s), and group 3 (n = 41) appeared to have recently passed a stone. LFTs in groups 2 and 3 were also analysed at maximal liver enzyme derangement, maximum hyperbilirubinaemia and during acute pain episodes.
Results: Group 1 had higher median bilirubin, AST and ALP levels than groups 2 or 3 (p < 0.001). In group 1, median rise in ALP exceeded that in AST (4.3 x normal upper limit (NUL) vs. 2.6 x NUL, p < 0.01), but in groups 2 and 3, AST and ALP were similarly elevated (both approximately 2 x NUL). At the time of maximum enzyme derangement in groups 2 and 3, median AST elevation (4.4 x NUL, 185 IU/l) exceeded that for ALP (2.4 x NUL, 276 U/l), (p < 0.001), and this was also true at peak hyperbilirubinaemia in these groups (AST 3.6 x NUL, ALP 2.4 x NUL, p < 0.01. Similarly, severe pain episodes in groups 2 and 3 were accompanied by greater elevations in bilirubin and AST, but not ALP, compared with levels at ERCP.
Discussion: The conventional wisdom that ALP rises more than AST in obstructive jaundice holds true where the jaundice is due to strictures, but in obstructive stone disease, the rise in AST may equal that in ALP, or even exceed it during maximum jaundice and during painful episodes. Clinicians should consider the possibility of extrahepatic biliary obstruction, even when AST is the predominantly elevated enzyme.