AbstractBackground:Thrombocytopenia is common in the intensive care unit. Potential mechanisms and etiologiesbehind this phenomenon are multiple and often entangled. We assessed the effect of a systematic approach, usingroutinely available tests, on the proportion of patients in whom the mechanism (primary objective) and etiology(secondary objective) of thrombocytopenia in a mixed intensive care unit (ICU) could be identified.Methods:Before-and-after study of all patients with thrombocytopenia was used.‘Before’group had no intervention.New standard operating procedures for thrombocytopenia management were introduced. In the‘After’group, bonemarrow aspiration; determination of fibrinogen dosage, prothrombin time, factor V, D-dimers; assay of fibrin monomers,ferritin, triglycerides, lactic acid dehydrogenase, aspartate transaminase, alanine aminotransferase, vitamin B12,folates,reticulocytes, haptoglobin, and bilirubin were performed.Results:In the Before group (n= 20), the mechanism (central, peripheral, or mixed) was identified in 10 % versus 83%in After group (n=23)(p< 0.001) (48% peripheral, 35% mixed). Before intervention,≥1 etiology was identified in 15%versus 95.7% in the After group (p<0.001).Conclusions:Systematic and extensive investigation using routine tests highlights the mechanisms and etiology ofthrombocytopenia in most cases.