BACKGROUND: Preoperative bleeding time (BT) does not correlate with postoperative bleeding in patients subjected to surgical procedures. A significant positive correlation has been reported between the BT 2 hours after cardiopulmonary bypass surgery and the nonsurgical blood loss during the first 4 hours after bypass surgery. This study was done to investigate the effect of Hct and platelet count on the BT measurement in normal, healthy men and women.

STUDY DESIGN AND METHODS: To assess the relative effect of RBCs and platelets on the BT, 22 healthy male and 7 healthy female volunteers were subjected to the removal of 2 units of RBCs (360 mL), followed by the return of the platelet‐rich plasma (PRP) from both units and the infusion of 1000 mL of 0.9‐percent NaCl. Four of the men and all seven women received their RBCs 1 hour after their removal. Shed blood levels of thromboxane B₂ (TXB₂), 6‐keto prostaglandin F_1α, and peripheral venous Hct were measured. BTs were measured in 15 men and 13 women before and after a plateletpheresis procedure to collect 3.6 × 10¹¹ platelets per unit.

RESULTS: The 2‐unit RBC apheresis procedure produced a 60‐percent increase in the BT associated with a 15‐percent reduction in the peripheral venous Hct and a 9‐percent reduction in the platelet count. The plateletpheresis procedure produced a 32‐percent decrease in the platelet count, no change in peripheral venous Hct, and no change in the BT. After the removal of 2 units of RBCs, the shed blood TXB₂ level decreased significantly. Reinfusion of 2 units of RBCs restored the BT and restored the TXB₂ level to the baseline levels.

CONCLUSION: The acute reduction in Hct produced a reversible platelet dysfunction manifested by an increase in BT and a decrease in the shed blood TXB₂ level at the template BT site. Return of the RBCs restored both the BT and the shed blood TXB₂ level to normal. The platelet dysfunction observed with the reduction in Hct was due in part to a reduction in shed blood TXB₂ and other, unknown mechanisms.