Missingness matters: a secondary analysis of thromboelastography measurements from a recent prehospital randomized tranexamic acid clinical trial

Background Tranexamic acid (TXA) has been hypothesized to mitigate coagulopathy in patients after traumatic injury. Despite previous prehospital clinical trials demonstrating a TXA survival benefit, none have demonstrated correlated changes in thromboelastography (TEG) parameters. We sought to analyze if missing TEG data contributed to this paucity of findings. Methods We performed a secondary analysis of the Study of Tranexamic Acid During Air Medical and Ground Prehospital Transport Trial. We compared patients that received TEG (YES-TEG) and patients unable to be sampled (NO-TEG) to analyze subgroups in which to investigate TEG differences. TEG parameter differences across TXA intervention arms were assessed within subgroups disproportionately present in the NO-TEG relative to the YES-TEG cohort. Generalized linear models controlling for potential confounders were applied to findings with p<0.10 on univariate analysis. Results NO-TEG patients had lower prehospital systolic blood pressure (SBP) (100 (78, 140) vs 125 (88, 147), p<0.01), lower prehospital Glascow Coma Score (14 (3, 15) vs 15 (12, 15), p<0.01), greater rates of prehospital intubation (39.4% vs 24.4%, p<0.01) and greater mortality at 30 days (36.4% vs 6.8%, p<0.01). NO-TEG patients had a greater international normalized ratio relative to the YES-TEG subgroup (1.2 (1.1, 1.5) vs 1.1 (1.0, 1.2), p=0.04). Within a severe prehospital shock cohort (SBP<70), TXA was associated with a significant decrease in clot lysis at 30 min on multivariate analysis (β=-27.6, 95% CI (-51.3 to -3.9), p=0.02). Conclusions Missing data, due to the logistical challenges of sampling certain severely injured patients, may be associated with a lack of TEG parameter changes on TXA administration in the primary analysis. Previous demonstration of TXA's survival benefit in patients with severe prehospital shock in tandem with the current findings supports the notion that TXA acts at least partially by improving clot integrity. Level of evidence Level II.