Platelet count in trauma patients

Close to 20 % of those suffering significant trauma develop thrombocytosis (raised platelet count) in the days and weeks following injury. Although this thrombocytosis is associated with increased risk of complications during recovery, it is also associated with decreased risk of death and thus may have overall protective value. 

These are the headline findings of a recently published US study aimed at examining the clinical significance of posttraumatic thrombocytosis. The focus of this retrospective study was all 3286 trauma victims admitted to a Californian surgical intensive care unit during a 7-year study period (1998-2005). Thrombocytosis, defined as platelet count > 450 × 103 /mm3 (> 450 × 109/L), developed in 614 (18.7 %) patients. 

Extreme thrombocytosis, defined as platelet count > 1000 × 103 /mm3 (> 1000 × 109/L), occurred in 41 (1.2 %) patients. For a small minority (12 %) of patients with thrombocytosis, platelet count rose above normal within 7 days of injury but for the vast majority onset of thrombocytosis was delayed until at least the second week following injury. 

Analysis of all study patient records revealed that injury was more severe in those with thrombocytosis compared with those without thrombocytosis. Furthermore there was a clear association between thrombocytosis and a range of posttrauma complications: sepsis, multiple organ dysfunction, pneumonia, acute respiratory distress syndrome, renal failure and venous thromboembolism. 

One or more of these complications occurred in 55 % of patients with thrombocytosis. By comparison only 17 % of patients whose platelet count remained within normal limits suffered any complication. Despite these associations those with thrombocytosis were found to be more likely to survive their injury. 

Of the 3286 study population, 506 died before discharge, giving an overall mortality rate of 15.4 %. Mortality rate among those with thrombocytosis was just 3.8 %, significantly less than the 18.1 % mortality rate among those whose platelet count remained normal. Just why those with raised platelet count should have a better chance of surviving severe injury remains unclear.