Flags indicating abnormal coloration of urinary glucose in US-3500 automatic urine analyzer

Abstract

There are two methods of urine qualitative analysis using urine test strips: visual judgement and instrumental judgement based on the results of an automatic urine analyzer. The analyzer has an additional function for judging abnormal coloration at the same time as judging concentration. In the measurement of urinary glucose concentration using the fully automated urine analyzer US-3500, we encountered multiple specimens in which flags indicating abnormal coloration were displayed but no abnormal coloration was observed by visual judgement. In this study, we investigated the cause of this discordance between visual and instrumental judgements. Because no abnormality was found in the comparison between the urinary glucose concentrations measured using the analyzer and urinary glucose quantitative values or in the measurements using multiple types of lot test strips, doubts were cast on the accuracy of the identification criteria for abnormal coloration of urinary glucose in the US-3500. We therefore asked the manufacturer to investigate it. In a plot created by applying the index calculated from the reflectance obtained from the measurement to the identification criteria for abnormal coloration, there were multiple specimens that were distributed near the identification line, indicating that the setting was such that flags for abnormal coloration were likely to be generated. This investigation led to the improvement of the US-3500’s instrumental parameters by the manufacturer. After changing the parameters, the number of specimens misjudged as abnormal coloration has been significantly reduced, and more accurate results of instrumental judgement are now available.