Diagnostic Utility of the Carbohydrate Antigen 19-9 (CA 19-9)/C-reactive Protein (CRP) Ratio for Predicting Malignancy in Obstructive Jaundice

Background: Differentiating malignant from benign obstructive jaundice remains difficult, particularly when conventional tumour markers are elevated by cholestasis or superimposed inflammation.Carbohydrate antigen 19-9 (CA 19-9) is widely used in pancreatobiliary malignancy, but its value is reduced in benign biliary obstruction.C-reactive protein (CRP), an inflammatory marker, may help contextualise CA 19-9 elevation.Objective: The primary objective was to determine the diagnostic discrimination of the CA 19-9/CRP ratio for malignancy among patients with obstructive jaundice.Secondary objectives were to compare its observed performance with that of CA 19-9 alone and the CA 19-9/bilirubin ratio, and to estimate an exploratory threshold with corresponding sensitivity and specificity.Methodology: This comparative cross-sectional study was conducted in the Department of Hepatobiliary, Pancreatic and Liver Transplant Surgery, Bangladesh Medical University, Dhaka, over one year.Ninety adult patients with obstructive jaundice were enrolled by purposive sampling: 45 with malignant obstruction and 45 with benign obstruction after definitive diagnosis by imaging, operative findings, and histopathology where applicable.Serum CA 19-9, CRP, and bilirubin were measured in all participants.Group comparisons were performed using the chi-square test, Fisher's exact test, Student's t-test, or Mann-Whitney U test as appropriate.Receiver operating characteristic analysis was used to determine discriminatory performance.Results: Patients with malignant obstruction were older than those with benign disease (57.42 ± 8.4 vs. 44.82± 16.18 years, P = 0.001).Median CA 19-9 was higher in malignant than in benign obstruction (370 vs. 41.4U/mL; P = 0.004).Median CRP was lower in malignant than in benign obstruction (15.2 vs. 88.0 mg/L; P = 0.001).The CA 19-9/CRP ratio was higher in malignant than in benign obstruction (42.92 vs. 0.70; P = 0.001).On receiver operating characteristic analysis, the CA 19-9/CRP ratio had the strongest performance for predicting malignancy, with an area under the curve of 0.812, a sensitivity of 84.4%, a specificity of 71.1% and an optimal cut-off of 7.23.This exceeded the performance of CA 19-9 alone (area under the curve 0.677) and the CA 19-9/bilirubin ratio (area under the curve 0.619).Conclusions: The CA 19-9/CRP ratio demonstrated better discriminative ability than CA 19-9 alone for identifying malignant obstructive jaundice in the study participants.This inexpensive and readily available ratio may be useful as an adjunctive preoperative marker, especially where access to advanced diagnostic modalities is limited.