Analysis of annual distributions of hemoglobin A2 values as a method to test for HbA2 standardization

Background and aims: The monitoring of yearly distributions of HbA(2) measured has been indicated as a reliable indicator of worldwide standardization.Materials and methods: Measurements/year of HbA(2) have been collected over three consecutive years in 15 Italian laboratories each using the same analytical method over three years period. HbA(2) distributions, cleaned of replicated measurements, were compared by the overlapping area of the raw probability density functions expressed by coefficient eta (eta), and by comparing the reference intervals for the central part of each distribution estimated by the indirect method refineR using the R package "refineR".Results: According to the overlapping areas analysis the distributions/year of the data provided by 4 centers able to perform at least 1000 measurements/year were similar in 2 consecutive years. Moreover, the reference intervals provided by 2 centers using the same analytical methods in two separate locations over the three consecutive years, were very similar. The highest overlap (99.7 %) was observed in one center over two consecutive years. The overlapping areas were very high (93.6-95.7%) in 8 out of 9 inter comparisons.