External Quality Assessment in laboratory medicine: is there a rationale to determine frequency of surveys?

Frequency of EQA surveys vary greatly between organisations, countries, discipline and analyte. They may be determined by: scientific opinion, clinical opinion; related to the prevalence of a disease; the relative frequency of laboratory analysis, a function of the analytical complexity of the investigation, a feature of the error rate of the investigation or simply based on availability or cost of the sample. Recently a survey was undertaken on EQA Schemes in Laboratory Medicine to determine the frequency of rounds per year and the number of samples distributed per round. The median for all disciplines was 4 rounds per year, with 28% of all Schemes having a frequency of 4 times per year. Similar results were observed for Haematology and Microbiology with a median of 3 rounds a year with 46% and 49%, respectively operating a frequency of one or two rounds per year. The median for Biochemistry was 6 rounds per year with 33% of Schemes having a monthly frequency. The number of samples per round varied from 1 (31%) to more than 20 (0.5%), with the majority of Schemes providing between 1 and 3 samples per round (83%).