Preeclampsia (PE) is a leading cause of maternal and perinatal morbidity, and progression to haemolysis, elevated liver enzymes and low platelets (HELLP) syndrome carries serious maternal and neonatal consequences. Early recognition is difficult because the routinely available haemodynamic and laboratory markers are individually non-specific. We set out to identify independent predictors of HELLP syndrome among routinely measured variables in women with established preeclampsia, and to assess the discriminatory performance of a combined panel. A retrospective cohort analysis was performed in 72 women with preeclampsia who delivered in the Department of Obstetrics in Henan Provincial People’s Hospital between January 2022 and December 2024. Twenty-seven women who developed HELLP syndrome were compared with 45 who did not. Haemodynamic and laboratory variables were recorded at the index time point, defined as the time at which HELLP syndrome was first clinically suspected. Between-group comparisons used the t test, the Mann–Whitney U test and the chi-square or Fisher exact test, with Bonferroni adjustment for the 15 comparisons performed. Independent predictors were identified by multivariable logistic regression, and discrimination was assessed by receiver operating characteristic (ROC) curve analysis, with exact confidence intervals for sensitivity and specificity. Neonatal survival was lower in the HELLP group (10/27, 37%) than in the preeclampsia group (31/45, 68.9%), and Apgar scores at 1, 5 and 10 min were lower ( P < 0.001 for each comparison). Gestational age at delivery was also lower, although the difference did not survive correction for multiple comparisons ( P = 0.004; P_Bonferroni = 0.059). After Bonferroni adjustment, systolic blood pressure (SBP), total bilirubin (TB) and alanine aminotransferase (ALT) differed significantly between the groups; platelet count lay at the threshold of significance ( P = 0.003; P_Bonferroni = 0.050) and is not interpreted as an established between-group difference. Maternal age, primiparity, history of hypertension, body mass index, diastolic blood pressure, aspartate aminotransferase, lactate dehydrogenase, white blood cell count, haemoglobin and serum creatinine did not differ significantly after adjustment. Multivariable logistic regression identified TB (adjusted odds ratio [OR] 1.40 per µmol/L, 95% confidence interval [CI] 1.12–1.74; P = 0.003), ALT (OR 1.02 per U/L, 95% CI 1.00–1.04; P = 0.027) and SBP (OR 1.14 per mm Hg, 95% CI 1.04–1.25; P = 0.007) as independent predictors. The three-variable panel achieved an area under the curve (AUC) of 0.982 (95% CI 0.959–1.000), with a sensitivity of 100% (27/27; 95% CI 87.2–100.0%) and a specificity of 91.1% (41/45; 95% CI 78.8–97.5%) at the Youden-optimal threshold. Elevated SBP, ALT and TB are independent predictors of progression from established preeclampsia to HELLP syndrome, and their combination discriminates strongly between women who do and do not develop the syndrome at the point of clinical deterioration. The panel is intended as an adjunct to clinical assessment: it should prompt intensified monitoring, risk-stratified triage and multidisciplinary reassessment of the timing of delivery.