Thrombocytopenia in critically ill surgical patients: a case-control study evaluating attributable mortality and transfusion requirements

Background: That thrombocytopenia results in increased mortality or transfusion requirements has not been confirmed by previous studies. We performed a case-control study in which 36 patients who developed severe thrombocytopenia of less than 50 x 10(9) platelets/l were carefully matched for the severity of underlying disease and other important variables. Results: Seventeen (47%) thrombocytopenic patients died, versus 10 (28%) matched control patients who were not thrombocytopenic. Nine pairs had a discordant outcome, and in eight of these pairs the thrombocytopenic patient died (exact binomial probability 0.037). The estimated attributable mortality was 19.5% (95% confidence interval 3.2-35.8), and the estimated odds ratio was 2.7 (95% confidence interval 1.02-7.10). Thrombocytopenic patients had comparable values for severity of illness scores between day of admission and day of thrombocytopenia, in contrast with control patients who had a statistically significant decrease in severity of illness scores during the same period. Thirty (83%) of the thrombocytopenic patients required transfusion of blood products, versus 21 (58%) control patients (paired chi(2) test 4.92, P< 0.04). The estimated attributable transfusion requirement was 25% (95% confidence interval 5.4-44.6), and the estimated odds ratio was 1.52 (95 confidence interval 1.05-2.20). Conclusion: The present study suggests that thrombocytopenia of less than 50 x 10(9) platelets/l may be a marker for more severe illness and increased risk of death, rather than causative, because a true causal relationship is not established. Thrombocytopenia also leads to an excess of blood product consumption.