USE OF MEDIANS AND AVERAGE OF NORMALS OF PATIENTS DATA FOR ASSESSMENTOF LONG-TERM ANALYTICAL STABILITY

Using results from patients, we studied several methods for long-term (years) monitoring of the analytical stability of various chemistry te sts, For each test, we obtained on a bimonthly basis histograms of gre ater than or equal to 200 to similar to 2000 data points and determine d the median, mean, and mean of those data points in the reference ran ge (''average of normal'' or AON), Examining similar to 4 years' data, we found that the medians and AON are extremely stable for most tests , and that all observed shifts in the medians or in the AON could be e xplained by expected or unexpected changes in the laboratory, The mean s and peak values of the Erlang (y) distribution were less useful, owi ng to shifts caused by extreme outliers, especially for enzymes in ser um, We assumed that the underlying patient population and testing patt erns were stable, Mie recommend the use of medians or the AON of patie nts' data under defined conditions for monitoring the long-term analyt ical stability of certain tests involving serum or whole blood.