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pISSN 2950-9114 eISSN 2950-9122
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Original Article

J Lab Med Qual Assur 2017; 39(2): 76-82

Published online June 30, 2017


Copyright © Korean Association of External Quality Assessment Service.

Abnormal Urinalysis Results Caused by Interfering Substances

Wonmok Lee1, Yukyung Kim2, Soonhee Chang3, A-Jin Lee4, Chang-Ho Jeon4

1Department of Laboratory Medicine, Keimyung University School of Medicine, Daegu, Korea,
2Department of Laboratory Medicine, Yeungnam University College of Medicine, Daegu, Korea,
3Department of Laboratory Medicine, Daegu Fatima Hospital, Daegu, Korea,
4Department of Laboratory Medicine, Catholic University of Daegu School of Medicine, Daegu, Korea

Correspondence to:Chang-Ho Jeon Department of Laboratory Medicine, Catholic University of Daegu School of Medicine, 33 Duryugongwon-ro 17-gil, Nam-gu, Daegu 42472, Korea Tel: +82-53-650-4144 Fax: +82-53-653-8672 E-mail: chjeon@cu.ac.kr
전창호 우)42472 대구시 남구 두류공원로17길 33, 대구가톨릭대학교 의과대학 진단검사의학과 Tel: 053)650-4144, Fax: 053)653-8672, E-mail: chjeon@cu.ac.kr

Received: October 17, 2016; Revised: December 6, 2016; Accepted: December 8, 2016

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.



To understand causes of abnormal reaction for the urinalysis, we analyze the interfering substances of clinical urine samples. We focused the effect of urinary vitamin C and fluorescein sodium to the urine chemistry especially glucose, hemoglobin, and leukocyte esterase.


Incidence of urinary vitamin C was determined for patients and people underwent a medical check-up. We decided dipstick results of glucose, hemoglobin, and leukocyte esterase as false negative based on urine sediment and serum glucose results. Dipstick urinalysis was tested by URiSCAN Pro III with URiSCAN 11 strip (YD Diagnostics, Korea). Urine sediments tests were performed by manual microscopic analysis or Sysmex UF-1000i (Sysmex Co., Japan).


The incidence of vitamin C was 20.4% for all subjects. The positive rate of the medical check-up group (34.6%) was higher than others. When vitamin C was detected in clinical urine samples, 42.3%, 10.6%, and 8.2% were defined as false negative for glucose, hemoglobin, and leukocyte esterase dipstick tests, respectively. Fluorescein sodium also interfered on the results of hemoglobin and leukocyte esterase of the dipstick reagents.


Vitamin C was frequently found in the clinical urine samples, and its incidence was higher in the people who underwent medical check-up. The urinary vitamin C and fluorescein sodium can cause interferences in urine dipstick results. Thus, it is expected that present study will give useful information to predict false negative rates of urine dipstick tests by vitamin C and fluorescein sodium.

Keywords: Ascorbic acid, Fluorescein, Urinalysis, Interference

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