A novel approach to the assessment of variations in the human platelet count

This is the first report of a method to assess the significance of numerica l changes in the platelet count based upon a result exceeding the normal in tra-individual variation in platelet numbers. Serial platelet counts from 3 ,789 subjects were analysed to determine the intra-individual variation in platelet numbers. A platelet count difference of 98 X 10(9)/L in males was found to represent a change that would occur by chance in less than 1 in 1, 000 platelet count determinations. Tables to determine the significance of platelet number variations. given N previous observations, are provided at two probability levels. The repeatability of the platelet count was calcula ted as 0.871 (males) and 0.849 (females) indicating that the heritability o f platelet count is high and that the platelet count is predominantly genet ically determined. A seasonal variation in platelet count was found with a 'winter' versus 'summer' difference of 5.10 x 10(9)/L (males) and 5.82 X 10 (9)/L (females).