Serum calcium methodology--a Canadian assessment based on the application of the reference method

The reference method for serum calcium [J.P. Cali, G.N. Bowers Jr., D.S. Young (7)] has provided target values in six voluntary interlaboratory studies each using five or six human serum samples, mostly in liquid form. Eighteen method/instrument categories, used by at least five laboratories in the last two studies, have been rated in four classes for inter- and intra-laboratory accuracy and for precision. There has been a noticeable improvement in the performance of some individual laboratories but no real improvement in the overall results. Certain poor performance procedures were used less often in the most recent studies; however, some continue to be used. There has been a great increase in automated procedures but the results were not consistently reliable. There was wide diversity in the sources of supply of standards and quality control materials and their use in the laboratories. The wide variety of laboratory reference ranges (normal ranges) for the adult male was not consistent with the analytical results and differences in clinical interpretation occurred. On a daily workload basis the best procedures account for approximately 80% of the analytical tests performed per day whereas the worst procedures account for only 3% of the tests per day.