Stone or stricture as a cause of extrahepatic cholestasis--do liver function tests predict the diagnosis?

Cholestasis, roughly divided into intrahepatic and extrahepatic forms, is a clinical challenge. Extrahepatic cholestasis, characterized by dilated bile ducts, is caused by either a bile duct stone or stricture, with stricture most often related to a malignancy. The aim of the present study was to analyze the value of common liver function tests in separating patients with malignant bile duct strictures from those with stones.

All consecutive patients admitted for endoscopic retrograde cholangiopancreatography (ERCP) were included in the study population if a bile duct stricture related to a malignancy was found by ERCP (n=103) or if a bile duct stone was successfully extracted during ERCP, thus confirming the diagnosis of a stone (n=109). Plasma alkaline phosphatase, gamma-glutamyltransferase, alanine aminotransferase and bilirubin values were determined in the morning before ERCP.

Plasma bilirubin (p<0.001), alkaline phosphatase (p<0.001) and alanine aminotransferase (p=0.040) levels were significantly higher in patients with malignant bile duct strictures than in those with bile duct stones. In addition, gamma-glutamyltransferase levels seemed to be higher in patients with malignant strictures than in those with stones, although the difference did not reach statistical significance (p=0.053). In receiver operating characteristic analyses, bilirubin proved to be the best laboratory test in differentiating patients (p=0.001 vs. alkaline phosphatase, p<0.001 vs. alanine aminotransferase and p<0.001 vs. gamma-glutamyltransferase). With a plasma bilirubin cutoff value of 145 micromol/L, four out of five patients were categorized correctly.

Plasma bilirubin seems to be the best liver function test in distinguishing patients with malignant bile duct strictures from those with bile duct stones. This routine test should receive more attention in clinical decision-making than has previously been given.