On the performance and reliability of mechanized urine teststrip measurement in comparison with visual reading

Prescreening of urine specimens by teststrips is a valuable procedure for reducing the work load of the urine analysis laboratory: positive results for leukocytes, erythrocytes (haemoglobin), protein, and/or nitrite are widely used to select pathological specimens for subsequent microscopic examination. By standardization of the measurement conditions, mechanized teststrip reading is claimed to give more reproducible results than conventional techniques. To assess their ability to improve urine prescreening, especially with regard to the comparability of the results, the practical and analytical performance of three commercially available analysers (Rapimat II/T from Behringwerke AG, Urotron RL9 from Boehringer Mannheim GmbH, and Clinitek 200 from Ames/Bayer Diagnostic) was compared with visual reading. Analytical criteria were assessed using routine urine samples, while reproducibility was tested by repeated analysis of three different commercial control urines (Kova Trol from Madaus). A mean imprecision between 3% and 11.9% was found for the mechanized dipstick reading which was comparable to that found with visual examination (4.5% with Combur9-teststrips, Boehringer Mannheim GmbH). Due to the crude classification of the results, the different analysers as well as the visual technique gave quite different distributions for each of the semiquantitative parameters in the same urine samples. Even if statistical analysis was restricted to the frequency of positive results only, significant differences (chi 2-test, p less than 0.001-0.05) between methods were obtained, but these differences could not be attributed to one method alone. Using microscopic sediment analysis as reference, pathological urines were detected with a comparable sensitivity/specificity: Urotron 0.85/0.84, Rapimat 0.91/0.67, Clinitek 0.82/0.81, and duplicate visual reading 0.88/0.67 and 0.91/0.93. Mechanized teststrip reading had no obvious advantage with respect to the time required. We conclude: (i) no improvement in analytical performance or in speed of analysis could be claimed for mechanized methods in comparison with visual reading; (ii) mechanized teststrip reading might decrease the work load of the urine laboratory if integrated into a computerized laboratory system; (iii) mechanized teststrip reading will become analytically advantageous over visual reading if a more refined classification of the results is achieved.