Analytical Goals. Analytical Goals. Valid data are essential in making medical decisions , the most important concepts used in judging analytical performance :- 1)Analytical accuracy : agreement between the best estimate of a quantity and its true value
there is a basic distinction in performance requirement for two purposes , for monitoring therapy or following the course of disease the concentration of one or more substance is compared with the value obtained previously on the same patients, in this case the day to day observation must be reliable, and precision or reproducibility is the prime concern for diagnosis on other hand, the concentration of one or more substance is compared with the established reference range or discrimination values to determine if the value for the subject .
Lab. Analysis : is used to screen for disease , an abnormal value may not lead to immediate therapy
Test to determine prognosis is an extension of the diagnosis into future , accuracy are not rigid as for the initial diagnosis . for example whether the serum prostatic acid phosphatase is 5 u or 6 u /l would make little difference in predicting the course of prostatic carcinoma but equal error in activity of 1u/l could be critical in the initial detection of this tumor
In emergency the timeliness of a report may be of such importance that a somewhat lower standard of performance in term of accuracy or precision is acceptable .
furthermore on practical scale, there was ,for many analyte , no agreement on the true value among laboratories nor was their agreement on reference methods to obtain such a value.
frequently and there is a need for standardization of both analytical result and reference range among lab. Studies of patient or of groups of patients often extended over long period of time .
Gilbert approach reflect trust in the mean of values from many participating labs. As an approach to establishment of the true value for analyte .
Accuracy performance as judged by clinical lab. Values for bias in table 2 was within 2% for 9 of the 13 substances tested at the level shown.