When Enzymes Mislead: Assessing the Value of MRCP in Suspected Choledocholithiasis

The diagnosis of choledocholithiasis (CDL) requires balancing timely intervention against the risks of unnecessary invasive procedures. Although liver function tests (LFTs) are widely used for risk stratification, their static values and short-term trends remain poorly defined in predicting persistent common bile duct stones. This study evaluated the association between static and dynamic LFTs and CDL and assessed the diagnostic performance of magnetic resonance cholangiopancreatography (MRCP).

A retrospective review was conducted at Middlemore Hospital involving 504 acute inpatient MRCP scans within 2022. The collected clinical variables included patient demographics, LFTs and imaging modalities. 2 × 2 tables were constructed for those who had both MRCP and ERCP to assess the diagnostic utility of MRCP. Logistic regression and linear mixed-effects models were used to analyse the association between LFTs and CDL. Receiver operating characteristic curve analysis was performed to assess the diagnostic performance of each LFT.

Of 504 MRCPs, 131 (26%) were positive for stones. Bilirubin, alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT) were significantly higher in the CDL group on admission and repeat testing. Paradoxically, CDL was associated with a downward 24-h trend in ALP and GGT. Elevated GGT demonstrated the strongest independent association with CDL (adjusted OR: 5.27, 95% CI: 2.46-13.21; p < 0.001). Discriminatory performance of individual enzymes was modest (AUC: ALP 0.69; GGT 0.68; bilirubin 0.63). Among 157 patients undergoing both MRCP and ERCP, MRCP demonstrated high sensitivity (91.4%) but low specificity (32.7%).

Static and dynamic LFTs provide limited discrimination for persistent CDL and improving biochemical trends do not reliably exclude stones. This study underscores the diagnostic utility of MRCP to prevent both missed CDL and avoidable ERCP, and the need for standardised diagnostic protocols.