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SUMMARY Over the past decade interest in and knowledge about the role of platelets in the haemostatic process and in various pathological conditions has continued to grow. The scope of laboratory methodology to investigate platelet function in clinical haemorrhagic and thrombotic disorders in the specialised haemostasis unit has also proportionally widened. After highlighting the physiological processes of the role of platelets in the haemostatic mechanism this brief review comments critically on the available routine techniques used to study platelet function in patients who present primarily with a bleeding tendency. Physiology of platelet function in haemostasisHaemostatic reactions can be classified into several overlapping and sequential events: localised vasoconstriction at the site of vessel injury: platelet adhesion to exposed subendothelial basement membrane and collagen fibres; formation of a platelet aggregate or plug; activation of the coagulation cascade leading to formation of fibrin, which reinforces the platelet plug; and finally, activation of the fibrinolytic system, which digests the haemostatic plug and allows growth of new vascular endothelial cells to complete the repair process.' Platelets circulate as non-nucleated discs and consist of a trilaminar phospholipoprotein membrane with submembrane circumferential contractile filaments, three types of granules, and an irregular internal network of canaliculi, through which the granule contents can be released on to the platelet surface.2The granule types are: dense granules which release adenosine diphosphate (ADP), adenosine triphosphate (ATP), serotonin, and calcium ions; a granules whose release constituents include platelet derived growth factor, platelet factor 4 with heparin neutralising ability, fi thromboglobulin, factor VIII related antigen/von Willebrand factor; factor V, fibrinogen, fibronectin, and probably thrombospondin; and lysosomal granules. Table 1 summarises the subsequent interactions with circulating platelets, which occur after damage to the vessel wall. When the vessel wall is damaged

Three family members from three successive generations presented with a moderate bleeding tendency and a functional platelet defect. They had absent aggregation with arachidonic acid (0.6--3 microM), reversible aggregation with ADP (4 microgram) and cyclic endoperoxide analogues, single wave aggregation only with adrenaline (5.4 microgram) and a prolonged template bleeding time (> min). Malondialdehyde formation was reduced after N-ethylmaleimide stimulation (2--6 nmol/10(9) platelets; control values 8--12 nmol) and serum thromboxane B2 values were reduced (33--101 ng/ml; control values 200--700 ng/ml). When the platelets were incubated with [3H]arachidonic acid the final metabolite of the lipoxygenase pathway (HETE) was produced in normal amounts but the production of thromboxane B2 and HHT was decreased whereas prostaglandin F2a, and E2 and probably D2 were increased. Evidence for enhanced production of prostaglandin D2 was also provided by the rise in the patient's platelet cyclic AMP levels following stimulation with arachidonic acid. The patient's washed platelets stimulated the production of 6-keto PGF 1a by aspirin-pretreated cultured bovine endothelial cells. The plasma levels of 6-keto PGF1a (439--703 pg/ml; normal 181 +/- 46 pg/ml) were raised. The decreased production of thromboxane B2, HHT and malondialdehyde and increased formation of prostaglandin F2a, E2, D2 and of 6-keto PGF1a are compatible with a partial platelet thromboxane synthetase deficiency and reorientation of cyclic endoperoxide metabolism. The markedly prolonged bleeding time would result not only from reduced formation of thromboxane A2 but also from increased production of the aggregation inhibiting prostaglandins PGI2 and PGD2.

The yield of diagnostic-therapeutic protocols depends largely on the context of care in which they are applied. This paper documents the importance of including epidemiological research in interventions for cooperation in complex health areas such as pediatric oncology.