Typical platelet count courses in ICU patients show how the dynamic of the platelet count can be used to differentiate between different causes of thrombocytopenia in the critically ill patient. The grey background area shows the platelet count course of 553 patients after cardiopulmonary bypass surgery obtained from a prospective study,¹³  excluding patients with persistent thrombocytopenia or later onset thrombocytopenia. (a) The normal platelet count patterns observed in patients undergoing major surgical interventions. The platelet count nadir is typically reached by days 3 and 4 for major surgery (inserted graph). A platelet count of 50 to 100 × 10⁹/L during this time period is nearly always related to postoperative consumption and dilution. Different types of surgery show slightly different patterns in regard to the postsurgery platelet count decrease (time and nadir), the time to reach the presurgery platelet count level, and the dynamics of the postsurgery rebound. The different lines exemplify typical platelet count patterns based on summarized data,^12,15  but are not real patients. **Data for the orthopedic surgery patients given in the insert of (a) have been kindly provided by Dr T. E. Warkentin, McMaster University, Canada. (b) Early-onset thrombocytopenia in surgical patients (solid line) and medical patients (dot-dash line) are caused by major platelet consumption (eg, sepsis, multiorgan failure or aggravation of the underlying disease). The second solid line indicates a platelet count pattern typical for late-onset complications in a surgical ICU patient. The first decrease in platelet counts is caused by major surgery (compare with (a)). After initial start of platelet counts recovery, late-onset nonimmune complications cause a gradual decrease of platelet counts. (c) Late-onset rapid decrease of platelet counts is typical for immune-mediated thrombocytopenia, which typically occurs in the second week of treatment (after surgical intervention, heparin, and other drugs). Arrows indicate the typical range of platelet count nadirs. Transfusion-related passive alloimmune thrombocytopenia can occur any time, but is closely related to transfusion of plasma-containing blood products.