Acceptable variability in external quality assessment programmes for basic semen analysis.

BACKGROUND External quality assessment is essential in modern andrology laboratories. To assess the proficiency of laboratories participating in an external quality assessment programme (EQAP), limits for acceptable variability must be determined. Limits currently specified largely depend on criteria set by the organizers of individual EQAP schemes. The objective of this study was to evaluate the different criteria described in ISO 13528: 2005 for calculating acceptable variability in EQAP when applied to basic semen analysis parameters. METHODS AND RESULTS The data used in this study were the means and standard deviations obtained for independent samples from two EQAPs, one national (Spanish) and one international (European). The acceptable variability according to ISO 13528: 2005 was calculated using four types of criteria: (i) ± 3 standard deviations of the results of all participating laboratories; (ii) ± 3 standard deviations of the results of expert laboratories; (iii) quality specifications based on biological variability, state-of-the-art and clinicians' opinions and (iv) the same quality specifications adjusted for the uncertainty of the assigned value. The first two strategies resulted in very wide ranges of acceptable variability. Conversely, the strategy based only on quality specifications resulted in very narrow ranges. For the fourth strategy, acceptable ranges were intermediate between the results produced with the other strategies. The third and fourth strategies did not produce observable differences in acceptable ranges when the model used for calculating the specifications of analytical quality was changed. CONCLUSIONS It is essential that EQAPs for semen parameters should determine the ranges for acceptable variability in results. Moreover, these ranges must be clinically useful, i.e. the variability should have a minimal negative impact on clinical decisions. The exact definition of 'expert laboratory' is more important than the model chosen for estimating analytical quality specifications in an EQAP for semen parameters in basic semen analysis.