An examination of false reaction factors on creatinine test strips

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  • クレアチニン試験紙の偽反応を起こす要因についての検討

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Abstract

<p>Creatinine test strips have been developed in recent years, and the urine protein-to-creatinine ratio (P/C ratio) in random urine specimens can easily be measured by the test strip method. Nevertheless, just like other test items, we often encounter a situation wherein false reactions (false positive, false negative, and false color reactions) in a routine laboratory test deviate significantly from the quantitatively determined values. It has been reported that a false reaction of a creatinine test strip may occur in the presence of hemoglobin or myoglobin, or when patients are taking cimetidine, etc. We investigated the root cause of false reactions using clinical specimens that showed a false reaction in a creatinine test strip method. The semiquantitatively determined creatinine levels in some specimens were higher than the quantitatively determines levels, and we confirmed that this inconsistency occurred owing to the intake of cimetidine, as previously reported. On the other hand, the semiquantitatively determined levels in some specimens were lower than the quantitatively determined levels, and we observed that they often occurred in colored urine or alkaline urine, which are not reported very often. Therefore, we checked the wavelength characteristics of CLINITEK Atlas XL for colored urine, and we examined the color of urine as influenced by alkaline urine pH. As a result, colored urine showed abnormal wavelength characteristics, and a high pH of alkaline urine resulted in a false creatinine level, i.e., lower than the quantitatively determined level. All urine samples over pH 9.0 showed a creatinine level more than 2 ranks lower. This examination suggested that colored urine and alkaline urine were some of the causes that lead to the false lower levels in the creatinine test strip method.</p>

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