In this retrospective observational study, Leal-Noval et al. found better long-term (1-year) functional outcome following traumatic brain injury (TBI) in patients that did not need allogeneic blood transfusion during their hospital stay.

The authors conducted a telephone-based survey in 309 patients and observed that 3 neurological scores were almost doubled in transfused patients. A propensity score match in 76 pairs did not change the significant result for one score. Scores were dichotomised as favourable and unfavourable. The transfusion trigger was a haemoglobin level of 8 g/dL aiming at 10 g/dL. Although the most likely explanation is that the association of injury severity and blood transfusion and therefore worse outcome is responsible for that result, extensive statistic information is provided in the supplementary material. Adjustment of odds ratios for poor clinical outcome identified higher rates of major cognitive dysfunction and disabilities at the 12-month follow-up. The authors interpreted it as a long-lasting negative effect of transfusion that even increases with time.

Although these results are congruent with the mass of observational data on transfusion outcomes, I would be very careful to trust each of them unless proper prospective data were available, for the following reasons: 1) the number of observations and propensity matches remains small; 2) the time of transfusion was not included; and 3) transfused patients were indeed more severely ill upon admission. There are two contradictory observational data cited for septic patients (with a better outcome in transfused patients), but prospective data from the TRISS trial did not confirm the beneficial effects of transfusion for this setting.

In my opinion, we read enough observational studies and we need prospective data from controlled trials.

– Thomas Frietsch