Low platelet count and elevated serum thrombopoietin after severe trauma

Platelet count is regularly low in patients after multiple trauma, mainly due to blood loss and dilution. Thrombopoietin (TPO) is the main regulator of the circulating platelet mass. Under several clinical conditions an inverse correlation between TPO and the circulating platelet mass was reported. Since platelets bind and internalize TPO, a platelet-dependent regulation of TPO was suggested. Thus, acute blood loss should be accompanied by elevated TPO. We measured serum TPO, platelets, interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) in 17 multiple traumatized victims. Blood was collected within 12 h after trauma as well as in the morning of days 2, 4, 6 and 9 after admission at the intensive care unit. Platelet count was low at admission and remained low until day 4. Thereafter platelets increased until day 9. TPO nearly doubled within the first 2 d, reaching its maximum on day 6. IL-6 was initially very high and steadily decreased until day 9. VEGF increased 3-fold during the 9 d. Statistically significant correlations of TPO were found with platelets and IL-6, but not with VEGF. In multiple traumatized patients low platelet count is followed by a rapid increase in serum TPO. This fits into the concept of a feedback regulation between circulating TPO and platelet mass.