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© 2018 Journal of Family Medicine and Primary Care | Published by Wolters Kluwer - Medknow 1148
The reliability and validity of
using the urine dipstick test
by patient self‑assessment
for urinary tract infection
screening in spinal cord injury
patients: Methodological and
statistical issues on reliability
and validity
Dear Editor,
We were interested to read the recent paper by Krit Duanngai
and colleagues published in September 2017 issue of the J Family
Med Prim Care.[1]
The authors aimed to evaluate the reliability of the urine
dipstick test by patients’ self‑assessment for urinary tract
infection (UTI) screening and to determine the validity of urine
dipstick test. The inter‑rater reliability was measured in the sense
of Kappa and validity of urine dipstick test was reported in
terms of sensitivity, specicity, positive and negative likelihood
ratio (+LR, −LR), positive predictive value (PPV), and negative
predictive value (NPV). The Kappa of urine dipstick test for
leukocyte esterase, nitrite, and combined leukocyte esterase and
nitrite were 0.09, 0.21, and 0.52, respectively. The combined
leukocyte esterase and nitrite urine dipstick test gave the highest
specicity (87%), PPV (60%), and NPV (93%). According to the
validity of urine dipstick test +LR for leukocyte esterase was 1.33
with 95% condence interval (CI) (0.40–4.42) and −LR was 0.94
with 95% CI (0.74–1.21).
However, these results are not the most appropriate estimates
to evaluate validity and reliability. Kappa has two crucial
disadvantages; first, it depends on the prevalence in each
category and the second weaknesses of the Kappa value is the
fact that it depends on the number of categories.[2‑4] To assess
reliability (agreement), appropriate methods are the intraclass
correlation coefficient (ICCC) or Bland–Altman plot for
quantitative variables and weighted Kappa for the qualitative
variable with more than two categories.[2‑4]
Moreover, we surprised when we looked at the range of LR+ and
LR−. To the best of our knowledge, LR+ can be changed from 1
to ∞ (the higher the LR+, the more accurate the test) and LR− can
be changed from 0 to 1 (the closer the LR− to 0, the more accurate
the test). Theoretically, when the value of LR+ is <1 and LR− is >1,
the diagnostic accuracy of the test is worse than ipping a coin![4,5]
We are facing such a situation in this study when looking at the
95% CI of the LR+. It means the accuracy of the mentioned tests
is not acceptable and should not be suggested for clinical purposes.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conicts of interest.
Sajjad Rahimi Pordanjani1,2,
Sohrab Iranpour3,4, Siamak Sabour2,5
1Department of Public Health, School of Health, Semnan
University of Medical Sciences, Semnan, 2Department of
Clinical Epidemiology, School of Public Health, Shahid
Beheshti University of Medical Sciences, 5Safety Promotion
and Injury Prevention Research Center, Shahid Beheshti
University of Medical Sciences, Tehran, 3Department
of Community Medicine, School of Medicine, Ardabil
University of Medical Sciences, 4Social Determinants of
Health Research Center, Ardabil University of Medical
Sciences, Ardabil, Iran
Address for correspondence: Dr. Siamak Sabour,
Department of Clinical Epidemiology, Safety Promotion and Injury
Prevention Research Center, School of Health, Shahid Beheshti
University of Medical Sciences, Tehran, Iran.
E-mail: s.sabour@sbmu.ac.ir
References
1. Duanngai K, Sirasaporn P, Ngaosinchai SS. The reliability
and validity of using the urine dipstick test by patient
self-assessment for urinary tract infection screening
in spinal cord injury patients. J Family Med Prim Care
2017;6:578-82.
2. Szklo M, Nieto FJ. Epidemiology beyond the Basics. 3rd ed.
Burlington, MA: Jones and Bartlett; 2014.
3. Sabour S. Reliability of automatic vibratory equipment
for ultrasonic strain measurement of the median nerve:
Common mistake. Ultrasound Med Biol 2015;41:1119-20.
4. Sabour S. Adherence to guidelines strongly improves
reproducibility of brachial artery flow-mediated
dilation. Common mistakes and methodological issue.
Atherosclerosis 2016;251:490-1.
Letter to Editor
Letter to Editor
Journal of Family Medicine and Primary Care 1149 Volume 7 : Issue 5 : September-October 2018
5. Robert M. Centor. Estimating confidence intervals of
likelihood ratios. Med Decis Making 1992;12:229-33.
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Website:
www.jfmpc.com
DOI:
10.4103/jfmpc.jfmpc_224_18
How to cite this article: Pordanjani SR, Iranpour S, Sabour S.
The reliability and validity of using the urine dipstick test by patient
self-assessment for urinary tract infection screening in spinal cord injury
patients: Methodological and statistical issues on reliability and validity.
J Family Med Prim Care 2018;7:1148-9.
© 2018 Journal of Family Medicine and Primary Care | Published by Wolters Kluwer - Medknow
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