[First two years of an external quality assurance program for urinalysis]

To analyze the first two years of a strip uroanalysis quality assurance scheme operating in Mexico.

The participants received 8 shipments of four controls each as dried tablets to be dissolved and analyzed with urine strips. The number of participants increased from < 50 in the 1st shipment to > 200 in the 8th. They assayed 6-10 analytes depending on the strip used and sent in 763 reports. For each report we calculated a score per analyte (n = 4), per shipment (n = 24 to 40) and a global score in the 8 shipments (n = 707 to 763 reports). The scores ranged from zero (excellent accuracy) to a maximum of 400 and were calculated by comparison with the modal value of about 600 American and Canadian laboratories which assayed the same controls using exclusively Bayer strips and instrumental readings.

The best score was for nitrites (global score of 3 in 741 reports) and the worst for specific gravity (58 in 744 reports); the other analytes had scores from 11 to 19 (Table 1). The scores of four types of methods (Table 2) showed the best results with Bayer strips and instrumental readings (score of 13 in 469 reports) and the worst with strips of other suppliers (scores of 28 for visual and 31 for instrumental readings) and intermediate with visual readings of Bayer strips (score of 21).

1. Our results led us to the decision to exclude from the program participants who do not use Bayer strips as our program may disorient them instead of helping to improve their assays. 2. We confirmed that instrumental readings perform better than visual readings. 3. The causes of suboptimal performance in specific gravity need to be explored.