Diagnostic pitfall of carryover: in automatic urine analyzers

Eren Vurgun 1 , Osman Evliyaoğlu 2 , Sembol Yıldırmak 3  and İbrahim Akarsubaşı 4
  • 1 Okmeydani Training and Research Hospital – Department of Medical Biochemistry, Istanbul, Turkey
  • 2 Okmeydani Training and Research Hospital – Department of Medical Biochemistry, Istanbul, Turkey
  • 3 Giresun University Faculty of Medicine – Department of Medical Biochemistry, Giresun, Turkey
  • 4 Gaziosmanpasa Taksim Training and Research Hospital – Department of Medical Biochemistry, Istanbul, Turkey
Eren Vurgun, Osman Evliyaoğlu, Sembol Yıldırmak and İbrahim Akarsubaşı

Abstract

Objective:

We aimed to find out whether there is significant carryover effect which causes false-positive hematuria on red blood cells (RBCs) in automatic urine chemistry (DIRUI H-800) and sediment (DIRUI FUS-200) analyzers.

Methods:

Twenty-four samples with gross hematuria selected as containing high RBC concentration and forty-eight samples which had both negative result in dipstick and 0/hpf in microscopic examination selected as containing low RBC concentration. Carryover% was calculated via the formula [carryover%=100×(b1−b2)/(a2−b2)]. Carryover effect within results was analyzed with Wilcoxon test.

Results:

Carryover% was very high (67%) in urine chemistry analyzer. Carryover% of urine sediment analyzer was found 0.4% whilst false-positive hematuria percentage was 87.5% for the first samples came after gross hematuria and 6.6% for the second samples. The first samples analyzed after gross hematuria had significantly higher (p<0.001) results than the second samples in both analyzers.

Conclusion:

In urine sediment analyzer, carryover% calculated by formula was found analytically sufficient, but it causes highly false-positive results due to diagnostic limit of hematuria (RBC>3/hpf) is low. To prevent carryover in both urine analyzers; washing procedures should be revised and the diagnostic effect of carryover should also be taken into account by biochemists.

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Turkish Journal of Biochemistry (TJB), official journal of Turkish Biochemical Society, is issued electronically every 2 months. The main aim of the journal is to support the research and publishing culture by ensuring that every published manuscript has an added value and thus providing international acceptance of the “readability” of the manuscripts published in the journal.

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