Personalized reference intervals for platelet count reduce the number of subjects with unexplained thrombocytopenia

The reference range for any blood tests is defined as the set of values 95% of the normal population falls within. When the value of a parameter varies according to specific physiological characteristics of investigated people, a single reference range is not sufficient, and personalized ranges are required. This is the case, for instance, of the normal values for hemoglobin concentration, which vary according to age and sex. Demonstration that platelet count progressively decreases with ageing and women have more platelets than men after puberty1-3 stimulated the search for personalized ranges also for this parameter, and customized reference intervals for the Italian population have been recently proposed based on the analysis of over 40,000 healthy subjects.4 According to this study, normal ranges for platelet count are: 165-473 x109 /L, regardless of gender, under 15 years of age; 136-436 and 120-369 x109/L in women and men, respectively, between 15 and 64 years; and 119-396 and 112-361 x109/L in women and men, respectively, over 64 years. So, both the upper and the lower limits of normal platelet count for children are higher than with the single range currently in use, while those for adults are lower