BACKGROUND Abnormal liver function tests(LFTs) in post-liver transplant(LT) patients pose a challenge in the timing and selection of diagnostic modalities.There are little data regarding the accuracy of endoscopic retrograde cholangiopancreatography(ERCP) and liver biopsy(LB) in diagnosing post-transplant complications.AIM To evaluate the diagnostic performance of ERCP and LB in patients with nonvascular post-LT complications.METHODS This single-center retrospective study evaluated patients undergoing both ERCP and LB for evaluation of elevated LFTs within 6 mo of LT from 2000 to 2017.Diagnostic operating characteristics including accuracy,sensitivity and specificity for various diagnoses were calculated for ERCP and LB.The R factor(ratio of alkaline phosphatase to alanine aminotransferase) was also calculated for each patient.RESULTS Of the 1284 patients who underwent LT,91 patients(74.7% males,mean age of 51)were analyzed.Anastomotic strictures(AS,24.2 %),acute cellular rejection(ACR,11 %) and concurrent AS/ACR(14.3 %) were the most common diagnoses.ERCP carried an accuracy of 79.1%(95 % CI:69.3-86.9),LB had an accuracy of 93.4%(95 % CI:86.2-97.5),and the combination of the two had an accuracy of 100%(95 % CI:96-100).There was no difference between patients with AS and ACR in mean R factor(AS:1.9 vs ACR:1.1, P=0.24).Adverse events did not differ between the two tests(ERCP:3.1% vs LB:1.1%,P=0.31).ConCLUSION In patients with abnormal LFTs after LT without vascular complications,the combination of LB and ERCP carries low risk and improves diagnostic accuracy over either test alone.