Predicting transfusions in cardiac surgery: the easier, the better: the Transfusion Risk and Clinical Knowledge score

Allogeneic blood products transfusions are associated with an increased morbidity and mortality risk in cardiac surgery. At present, a few transfusion risk scores have been proposed for cardiac surgery patients. The present study is aimed to develop and validate a risk score based on adequate statistical analyses joint with a clinical selection of a limited (five) number of preoperative predictors. The development series was composed of 8989 consecutive adult patients undergone cardiac surgery. Independent predictors of allogeneic blood transfusions were identified. Subsequently, five predictors were extracted as the most clinically relevant based on the judgement of 30 clinicians dealing with transfusions in cardiac surgery. A predictive score was developed and externally validated on a series of 2371 patients operated in another institution. The score was compared to the other existing scores. The following predictors constituted the Transfusion Risk and Clinical Knowledge score: age > 67 years; weight < 60 kg for females and < 85 kg for males preoperative haematocrit; gender - female; and complex surgery. At the external validation, this score demonstrated an acceptable predictive power (area under the curve 0.71) and a good calibration at the Hosmer-Lemeshow test. When compared to the other three existing risk scores, the Transfusion Risk and Clinical Knowledge score had comparable or better predictive power and calibration. A simple risk model based on five predictors only has a similar or better accuracy and calibration in predicting the transfusion rate in cardiac surgery than more complex models.