To optimize management of chronic liver disease (CLD), a simple and noninvasive test to determine oesophageal varices (EV) and liver fibrosis is necessary. We performed a cohort study in a single tertiary care centre in order to devise a simple index reflecting EV and liver fibrosis. We derived an index reflecting EV which resulted from portal hypertension (the first part) and evaluated the index's ability to detect liver fibrosis which resulted in portal hypertension (the second part). Five hundred fifty-six patients (the first part, n = 409, mean age = 55.4 years, EV prevalence = 34.0%; the second part, n = 147, mean age = 48.8 years, cirrhosis prevalence = 12.9%) with virus-related CLD were included. P2/MS [(platelet count [109/L])2/(monocyte fraction [%] × segmented neutrophil fraction [%])] was derived to detect EV. The area under the receiver-operating characteristic curve (AUROC) of P2/MS was 0.916 (95% confidence interval, 0.879-0.954) for detecting EV, and 0.905 (0.862-0.947) for detecting high-risk EV (grade ≥ II or with red colour signs). P2/MS had AUROCs of 0.952 (0.904-0.999) and 0.873 (0.792-0.955) for histological cirrhosis (METAVIR F4) and significant fibrosis (METAVIR F2-F4), respectively, which were significantly greater than those of AST-to-platelet count ratio index (0.658, P < 0.001; 0.644, P = 0.003) and FIB-4 (0.776, P = 0.031; 0.707, P = 0.026). The predictive values of P2/MS were maintained at similar accuracy in subsequent validation sets. Our study suggests that P2/MS comprising only the complete blood count results is an efficient and noninvasive marker reflecting the presence of EV and the grade of liver fibrosis in patients with virus-related CLD. An independent external validation of P2/MS is required.