Indirect estimation of clinical chemical reference intervals from total hospital patient data: application of a modified Bhattacharya procedure.

Indirect methods for the determination of reference intervals utilise as input the total bulk of test results from all admitted hospital patients. One of the strongest arguments in favour of the use of these indirect methods is that one automatically obtains a one to one relationship between the selected population sample and the category of people for which the test results are intended. A study was conducted of the suitability of a modification of the indirect Bhattacharya method, which also permits the evaluation of heavily skewed distributions. The robustness of the method was evaluated by studying the homogeneity, stability and reproducibility of the hospital population in terms of the statistical parameters of the input distributions and of the resulting reference intervals for creatinine, uric acid and alanine aminotransferase. Finally, the age- and sex dependency for 15 clinical chemical parameters was compared with reported literature data.