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Background: Patients with symptomatic cholelithiasis and suspected choledocholithiasis can be risk stratified into a low (<10%), intermediate (10-50%) or high probability (>50%) based on clinical predictors. Liver biochemistries are the first line tests and any abnormal liver test raises suspicion for impacted common bile duct stone. A bilirubin level > 4 mg/dl is considered a very strong predictor with high probability of CBD stone (>50%). Likewise, bilirubin level between 1.8-4 mg/dl along with dilated ducts on ultrasound is considered a very strong predictor. All other abnormal liver biochemistries other than bilirubin are considered moderate predictor with low probability (<10%). However, predictive value of liver biochemistry trends in detecting choledocholithiasis in intermediate probability group is not known.
Methods: Charts of all patients admitted with symptomatic cholelithiasis that had cholecystectomy and underwent work up including MRCP for CBD stone evaluation between the periods of Jan 2007 and Oct 2012 at a tertiary referral center were reviewed. All patients who received preoperative work up for suspected CBD stone including liver biochemistries on 2 occasions with at least 12 hours apart, and underwent either pre/post-operative endoscopic retrograde cholangiography (ERC) or intraoperative cholangiography (IOC) were included in the study. Patients with any intrinsic liver disease, or hepato-biliary malignancy were excluded.
Results: Of a total of 330 patients, 125 met the criteria for intermediate risk group and were included in final analysis. Mean age of all patients was 52±21 years with 37 % males (n=46). MRCP was positive for CBD stone in 26.4% of patients (n=33/125). CBD stone was present in 33% (n=41/125) patients as confirmed by either IOC (n=11/84) or ERCP (n=32/60). Sensitivities, specificities, positive and negative predictive values and accuracy of the tests were calculated for preoperative MRCP, trends in total bilirubin alone, alkaline phosphatase (ALP) alone, AST/ALT alone, total bilirubin in combination with ALP, total bilirubin in combination with AST/ALT, ALP in combination with AST/ALT, and total bilirubin in combination with ALP and AST/ALT for patients with intermediate risk group and for all patients (Table -1)
Conclusion: The sensitivity of an upward trend in hepatic transaminases, alkaline phosphatase and total bilirubin alone and in different combinations is low although some of them are comparable to that of MRCP in detecting CBD stone. MRCP has a high specificity in detecting CBD stone and this is matched by an upward trend in AST/ALT with a similar specificity. Thus in the intermediate group, proceeding with ERC may be a better option when an upward trend in the AST/ALT, ALP and/or total bilirubin are noted, instead of performing a more expensive alternative diagnostic MRCP testing.
Table 1

	MRCP	T. Bili	ALP	AST/ALT	Bili+ALP	Bili+AST/ALT	ALP+AST/ALT	Bili+ALP+AST/ALT
Sensitivity	51	27	49	22	52	43	55	60
Specificity	85	76	67	83	57	70	60	51
PPV	63	35	43	39	38	40	40	38
NPV	78	67	72	68	71	70	60	51
Accuracy	74.4	60	61	62	56	60	58	54