Role of thrombocytopenia as an independent prognostic marker in critically ill patients with multi organ failure

Abstract

Thrombocytopenia is one of the most common laboratory abnormalities in ICU patients. Thrombocytopenia is usually defined as a platelet count<150*109/L, while a count of <=50*109/L is taken to represent sever thrombocytopenia (Strauss et al., 2002). Low platelet counts are common in critically ill patients, at ICU admission or during a stay in the ICU. The incidence of thrombocytopenia in ICU patients has ranged from 15 to 58%, depending on the type of population and the threshold used to define thrombocytopenia (Kinasewitz et al., 2004). The incidence of thrombocytopenia (platelet count <150 * 109/L) in critically ill medical patients is 35% to 44% (Strauss et al., 2002). A platelet count of <100 * 109/L is seen in 20% to 25% of patients, whereas 12% to 15% of patients have a platelet count <50 *109/L. In surgical and trauma patients, the incidence of thrombocytopenia is higher, with 35 to 41% of patients having less than 100 *109/L platelets (Stephan et al., 1999). Typically, the platelet count decreases during the patients first four days in the intensive care unit (ICU) (Akca et al., 2002). The primary clinical relevance of thrombocytopenia in critically ill patients is related to an increased risk of bleeding. Indeed, severely thrombocytopenic patients with platelet counts of <50 *109/L have a 4-5-fold higher risk for bleeding compared to patients with higher platelet counts (Strauss et al., 2002). The risk of intracerebral bleeding in critically ill patients during intensive care admission is relatively low (0.3% to 0.5%), but 88% of patients with this complication have platelet counts below 100 *109/L (Oppenheim – Eden et al., 1999). Moreover, a decrease in platelet count may indicate ongoing coagulation activation, which contributes to microvascular failure and organ dysfunction. Regardless of the cause, thrombocytopenia is an independent predictor of ICU mortality in multivariate analyses (Vanderschueren et al., 2000). Several studies show that the severity of thrombocytopenia in critically ill patients is inversely related to survival. In particular, sustained thrombocytopenia over more than 4 days after ICU admission or a drop in platelet count of >50% during ICU stay correlates with a 4-to6-fold increase in mortality (Akca et al., 2002). The platelet count was shown to be a stronger independent predictor for ICU mortality than standard composite scoring systems, such as the Acute Physiology and Chronic Evaluation (APACHE) II score (Strauss et al., 2002). Many ICU patients do not have thrombocytopenia at ICU admission but experience decreases in platelet count in the ICU that often fall short of the criteria for thrombocytopenia. The pathophysiologic and prognostic significance of these declines in platelet count is unclear. After major surgical procedures, platelet counts decrease, then recover and overshoot the normal range within a few days (Warkentin et al., 2003). Thrombocytopenia was associated with longer ICU stays, a higher incidence of bleeding events, greater transfusion requirements, and higher mortality (Ben Hamida et al., 2003). Thrombocytopenia and a decline in platelet count may reflect the same pathophysiologic disturbances , including sepsis, disseminated intravascular coagulation, vitamin deficiencies, macrophage activation, drug – induced toxicity, and unidentified factors (Stephan et al., 2000). It was found that the platelet –count decline may be important than the absolute platelet count for predicting survival in critically ill patients with normal platelet counts at ICU admission (Warkentin et al., 2003). Finally thrombocytopenia in critically ill patients is likely a marker of illness severity. This is supported by the observation that critically ill patients with thrombocytopenia have higher Multiple Organ Dysfunction Scores (MODS), Simplified Acute Physiology Scores (SAPS), and Acute Physiology and Chronic Health Evaluation (APACHE) scores compared with patients admitted with normal platelet counts at the time of ICU admission (Vanderschueren et al., 2000).