Twenty-four-hour lactate dynamics and adverse in-hospital outcomes in acute pulmonary embolism treated with systemic thrombolysis: A retrospective cohort study

Objectives Admission lactate carries prognostic information in acute pulmonary embolism (PE), but the value of its early change in patients receiving systemic thrombolysis is unclear. We examined the association between 24-h lactate dynamics and an adverse in-hospital clinical course. Methods In this retrospective single-centre cohort, 40 consecutive adults who received systemic alteplase for acute PE (2024–2025) were analysed. In 35 patients the 24-h sample followed thrombolysis. The primary outcome was a composite adverse event (complicated or fatal clinical course). Admission (T0) and 24-h (T24) lactate, absolute Δ lactate and percentage clearance were assessed by ROC analysis and Firth-penalised logistic regression with 2000-resample bootstrap internal validation. Results The composite event occurred in 12 patients (30%). Admission lactate did not discriminate the outcome (AUC 0.56), whereas Δ lactate and percentage clearance did (AUC 0.88 for both; 95% CI 0.76–0.99 and 0.77–0.99, respectively; DeLong p = 0.84, the two AUCs did not differ). A Δ ≥ 0 mmol/L identified an adverse course with a sensitivity of 0.75 and a specificity of 0.82, and a T24 ≥ 4 mmol/L gave a specificity of 1.00. The association of Δ lactate persisted after adjustment for age and showed minimal optimism on bootstrap internal validation. Conclusions In this selected cohort receiving systemic thrombolysis, admission lactate did not reproduce the discrimination reported in broader PE populations, whereas 24-h lactate dynamics showed a stronger association with the adverse in-hospital course. Δ lactate should be regarded as a marker of concurrent severity rather than a predictor of treatment response; the candidate thresholds are hypothesis-generating and require prospective validation.