The long-term effect of external quality assessment on performance in service cytogenetics

In 1993 a nationwide cytogenetic external quality assessment program (EQA) was initiated in the Federal Republic of Germany. Presently, some 70 laboratories, representing approximately 90% of all cytogenetic diagnostic tests, are participating in the study. Based on the quality assessment scheme of the Association of Clinical Cytogeneticists (1988) in the United Kingdom, quality of chromosome preparation and speed of routine diagnostic services are being evaluated. As a result of continuous external quality assessment, the mean banding level of participating laboratories rose from below 400 bands per haploid set (bphs) in 1994 to approximately 450 bphs in 1999 in prenatal tests and from about 400 to approximately 500 bphs in postnatal tests over the same 5-yr period. The percentage of participants achieving a banding level of 400 bphs or higher rose from approximately 50% to 93% in prenatal tests and from 60% to 96% in postnatal tests. No significant differences were observed in banding scores achieved by private laboratories compared to university institutes. The impact of the assessment of interpretation, reporting, and documentation remains difficult to evaluate. Preliminary data point to a more stringent adherence to ISCN nomenclature in karyotype designation by participants.