Evaluation of Questor urine screening system for bacteriuria and pyuria.

Abstract

Aius-To evaluate the Questor automated bacteriuria and pyuria screening system; to compare its performance with that of a reference method; and to assess its usefulness in a routine clinical laboratory.Methods-The Questor urine screening system was compared with a comprehensive regimen to detect urinary tract infection, using pour-plate viable counts to determine the numbers of bacteria present in urine samples, a wide range of other cultural methods, microscopic findings and clinical information. Results-The optimal performance in detecting significant growths was a sensitivity of 93%, a specificity of 74%, a positive predictive value of 43% and a negative predictive value of 98%. The list price per test is £0.17 and the capital cost of the system is £39 950. Questor can test 50 samples an hour and can be operated by one member of the laboratory staff, who is not required to make interpretative judgments-for example, a medical laboratory assistant. Conclusions-The sensitivity and specificity of the Questor was better than that obtained from other screening systems using the same protocol. The system was easy to use and is a useful addition to the methods available for screening for bacteriuria. Urinary infections are second only in prevalence to those of the upper respiratory tract. But the number of requests submitted to clinical microbiology laboratories for the microbiological examination of urine far exceeds the number of upper respiratory tract specimens. Bacteriuria may be chronic, persistent, and possibly influence structure and function outside the urinary tract. It has an important role in disease throughout life, from prematurity to hypertension and renal failure.' Many methods for screening for bacteriuria have been described and reviewed,2 but there remains a need for an accurate, rapid, cost effective system for use in routine clinical laboratories. Questor (Difco Laboratories Ltd, East Molesey, Surrey) is an automated system which is designed to categorise and enumerate bacteria and other cells found in urine using particle counting technology.An evaluation of the system was commissioned by the Medical Devices Directorate of the Department of Health and carried out at the Leicester Public Health Laboratory.The system's performance was compared with a comprehensive reference method which included a variety of cultural techniques, microscopic examination, and clinical information. A full report of the evaluation has been produced.' Methods The Questor system (fig 1) is an automated single-channel impedance particle counter which uses a direct physical method to count and categorise particles. A 100 PI aliquot of the urine to be tested is pipetted into one well of an eight-well disposable plastic tray which is then placed in the instrument. The following automatic process is then carried out. The specimen is diluted with a conductive electrolyte solution and offered to a particle counting probe (fig 2). There is a small orifice (A) in the glass end of the probe which also contains two platinu...

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