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We hypothesised that lactate concentrations are independently associated with massive transfusion in patients with primary postpartum haemorrhage. Moreover, combining lactate concentrations with the shock index, defined as the ratio of heart rate to systolic arterial blood pressure, can improve the predictive performance for massive transfusion.We retrospectively analysed patients with primary postpartum haemorrhage in the emergency department of a tertiary referral centre in Korea between January 1, 2004 and December 31, 2015.Of the 302 patients, 101 (33.4%) patients required massive transfusion. Lactate concentration was independently associated with the requirement for massive transfusion [odds ratio, 1.56; 95% confidence interval (CI), 1.31–1.87; P<0.01]. The area under the receiver operating characteristic curve of lactate concentration and shock index for massive transfusion was 0.788 (95% CI: 0.736–0.840; P<0.01) and 0.776 (95% CI: 0.717–0.836; P<0.01), respectively. Lactate elevation (>4.0 mM L−1) was associated with 86.1% specificity and 67.8% positive predictive value for massive transfusion. When combining elevated lactate concentrations (>4.0 mM L−1) with a shock index >1.0, the specificity and positive predictive value increased to 95.5% and 82.4%, respectively.Point-of-care testing of lactate concentrations in the emergency department may be useful to predict massive transfusion requirements in primary postpartum haemorrhage. Combining initial lactate concentrations with the shock index improves the predictive performance for massive transfusion requirements and may contribute to rapid risk stratification of patients with primary postpartum haemorrhage in need of transfusion and further focus on early interventions to control bleeding.