Longitudinal study of error prevalence in Pennsylvania physicians' office laboratories.

We examined the results of the low-volume-laboratory proficiency testing program for new physician office participants in the Commonwealth of Pennsylvania. Serum glucose, hemoglobin, urinalysis, throat culture, urine culture, and Gram's stain were included in the study. Quarterly error rates for each analyte were determined; between one fourth and all of the laboratories that made at least one error during the first two quarters of proficiency testing made at least one more error in the same analyte during the subsequent two quarters. We show that participation in the quarterly proficiency testing program for a 12- to 15-month period did not lead to a measurable increase in performance. For proficiency testing to be effective, we suggest that it be supplemented by additional methods to lower error rates, such as regulation or intensive consultation and training services for personnel of physicians' office laboratories.