[Resistance tests in general practice. Validity can be improved by standardized procedures]

Susceptibility testing of bacteria in urine is one of the commonest laboratory tests in general practice in Denmark. It is quick and easy to perform, but recent studies have shown low validity when the test is performed in general practice. If it is to continue as a diagnostic tool in general practice, its quality should be improved. The aim of this study was to investigate the effect of an intervention to improve the quality of susceptibility testing in general practice.

Twenty-three randomly selected general practices took part in the study. The intervention consisted of visits by laboratory technicians who instructed the practitioners in standardised procedures for susceptibility testing. Before and after the intervention, urine specimens containing monocultures of typical uropathogenic bacteria were sent to the practices. The practitioners performed susceptibility testing by the Sensicult and the Iso-Resagar methods, and the validity of the results before and after the intervention was compared. Results from susceptibility testing at the bacteriological laboratory, Odense University Hospital, were used as the gold standard.

The median frequency of correct results increased from 82% to 98% for susceptibility testing by the Sensicult method (p = 0.001) and from 90% to 96% by the Iso-Resagar method (p = 0.05).

The validity of susceptibility testing in general practice improves when preceded by instruction in standardised procedures.