Blood cell aggregation and screen filtration pressure

Action of aspirin on whole blood-aggregation evaluated by the screen filtration pressure method

BACKGROUND

There are few monitoring systems widely used in clinical practice for evaluating the effectiveness of aspirin therapy, so in the present study aspirin's antiplatelet effects we investigated with a whole blood aggregometer using a screen filtration pressure (SFP) method.

METHODS AND RESULTS

Thirty-five healthy male volunteers took 100 mg/day aspirin for 14 days. Whole-blood aggregation was analyzed at baseline and on days 7 and 14, using collagen and adenosine diphosphate as the stimuli, and compared with the platelet-rich plasma (PRP) aggregation measured by optical aggregometer. The platelet-aggregation threshold index (PATI) for both methods, which was defined as the putative agonist-concentration giving half-maximal aggregation, and the PRP-maximal aggregation rate were analyzed. The maximal aggregation rate induced by 1.6 mg/L collagen decreased from 85.5% (80.8-92.8) [median (interquartile range)] at baseline to 51.5% (39-63.8) on day 14 (p<0.0001). The PRP-PATI and whole-blood PATI for collagen increased from 0.32 (0.28-0.70) to 1.82 mg/L (1.25-2.89) (p<0.0001) and from 0.28 (0.22-0.3) to 1.06 mg/L (1.01-1.29) (p<0.0001) respectively.

CONCLUSIONS

The whole-blood PATI and PRP-PATI for collagen, as well as the maximal PRP aggregation rate, clearly distinguish platelet aggregability before and after aspirin intake. However, whole-blood analysis by the SFP-method is easier to perform, and is a promising method of monitoring aspirin's effects.

Platelet aggregability after splenectomy in patients with normosplenism and hypersplenism

The relationship between platelet count and aggregability was serially evaluated after splenectomy in patients with normosplenism and hypersplenism, and the results were compared with those found in patients undergoing only upper abdominal surgery. The preoperative count and aggregability of platelets were significantly suppressed in patients with cirrhosis of the liver, idiopathic portal hypertension, and prehepatic portal obstruction. However, the platelet aggregability of these patients markedly increased in accordance with the platelet counts after splenectomy. In the patients with normal splenic function preoperatively, splenectomy caused a simultaneous increase in platelet count and aggregability. The platelet function was not always reflected by the count in the patients with idiopathic thrombocytopenic purpura. On the other hand, in the control patients undergoing only laparatomy the platelet count substantially increased two weeks after operation, but platelet aggregability did not differ from the preoperative value. The present results suggest that additional factors for thromboembolism such as hypotension, acidosis, or stagnant blood flow should be avoided during the peak period of reactive thrombocytosis after splenectomy, and that an appropriate use of anticoagulants or inhibitors of platelet aggregation is recommended if and when necessary.