The use of patient data for the calculation of reference values for some haematological parameters

We have investigated the use of patient data for the calculation of reference values for the parameters which are determined by the Hemalog. For this purpose we used the Bhattacharya plot. All the parameters, with the exception of leukocytes, appear to meet the main underlying assumption of this plot, namely that the frequency distribution is Gaussian. In the case of leukocytes, however, the frequency distribution could be resolved into two overlapping Gaussian curves, thus making it possible to calculate reference values for this parameter also. The reference values as calculated from 14,500 unselected data (excluding children) are in general agreement with the literature. Significant differences were however detected between a group of patients and a group of blood donors. When a Bhattacharya plot has to be constructed with relatively few data, smoothing of the observed frequencies is very helpful in deciding which part of the plot is linear. Smoothing was carried out using the least squares method with a quadratic equation. Since the classes are equally spaced, this involves only a simple numerical transformation of the frequencies.