Application of Average of Normals (AON) for Evaluation of Short-Term Analytic Performance of Vitamin B12 Measurements

Objectives: In this study we used averages of normals technique to evaluate the analytical performance of vitamin B12 measurements. Additionally, this study is a preliminary work for verifying of reference interval given in kit insert. Material and Methods: Serum vitamin B12 measurements (n = 2106) were performed using Roche E170 immunochemistry analyzer. By using explore analysis in SPSS 11.5 program, outliers were eliminated and using this normalized data (n = 1884) mean value (X(population)), standard deviation (S(population)) and S(population) /S(measurement) ratio were calculated. Minimum patient number was calculated with the formula of N(population) = 2 x N(c) x (S(pop) /S(meas))(2). Truncation limits and control limits were calculated using X(pop) +/- 2 S(pop), and X(pop) +/- 2.58 S(pop) /N(pop)((1/2)) formulas. Results: The mean value was 323 pg/mL; truncation limits were 56.8 pg/mL as the lower limit and 628 pg/mL as the higher limit. Control limits calculated by using X(pop) +/- 2.58 S(pop) /(N(pop))(1/2) formula were 333 pg/mL as the lower limit and 351 pg/mL as the higher limit. Conclusions: In our opinion, this cost-effective technique can be used as an adjunctive control procedure to conventional QC applications in monitoring laboratory performance in terms of analytic stability.