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The cytobacteriological examination of urine is a biological test most commonly asked in the hospital. The results of a large part of urinary sample analyzed are negative, representing a heavy workload for bacteriology laboratories, burden that we would like to limit. In this context the aim of our study was to evaluate a screening test for urinary tract infection by urine dipstick compared to the reference method; th e cytobacteriological examination of urine finally promotes the realization of the urine dipstick before any urine culture. We selected 600 patients whom the physician asked the cytobacteriological examination of urine, and on every patient, we proceeded to urine collection and finally realized the urine dipstick before urine culture; two parameters on urine dipstick have helped us to confirm the negativity and positivity of the dipstick, its leukocytes and nitrites. The results of urine dipstick are positive if one or less of the two tests, leukocyte and nitrite is positive; the result is negative if both tests are negative. The urine culture was done on cled agar and bacterial identification was made on cultural characteristics, biochemical (API 2OE gallery of biomerieux). The results of urine culture were collected 72 hours after culture. For the analysis of results, the sensitivity, specificity, predictive values (positive predictive value and negative predictive value), the youden index, the proportion of correctly-classified subjects and the likelihood ratio (positive likelihood ratio and negative likelihood ratio) were calculated. The urine dipstick has the sensitivity of 96%, specificity of 90%, the positive predictive value of 74%, the negative predictive value of 98.8%, youden index of 0.86, the proportion of subjects correctly classified of 91.6%, a positive likelihood ratio of 9.6 and a negative likelihood ratio of 0.04. In the light of these results, the urine dipstick is an elimination test, by its very high sensitivity (96%), its high negative predictive value (98.8%) and negative likelihood ratio close to 0 or 0.04, and if the dipstick does not detect nitrite and leukocyte, the diagnosis of urinary tract infection is highly unlikely (<2% probability).

Urinary tract infection is the most common bacterial infection and causes a significant burden on health system resources. In the community, it mainly affects sexually active women but also people of all ages. In the hospital environment, the elderly and the carriers of the urinary catheters are the main affected patients. The concept of a urinary tract infection is broad, ranging from asymptomatic infection to pyelonephritis with sepsis [

This is a prospective and analytical study, carried out in Lubumbashi (DR Congo) and spread over six months (January-June 2017). The experimental setting was the laboratory of Lubumbashi University Clinics and provincial laboratory public health. The sample size of 600 subjects was based on convenience sampling. The target population consisted of patients consulting Clinics of Lubumbashi University and Provincial Public Health Laboratory. The inclusion criteria was each patient to whom the doctor asked for the cytobacteriological examination of urine. The exclusion criteria was each patient to whom the doctor did not ask for the cytobacteriological examination of urine. we proceeded to the collection of urine finally to make the urine dipstick before the urine culture, two parameters on the dipstick served us to confirm the negativity and the positivity of the strip; These are leukocytes, which testify to the reaction of the host to the infection whose principle is the demonstration of the activity of granulocyte esterases and nitrite whose principle is the demonstration of nitrite, therefore indirectly germs. positive nitrite (enterobacteria). The urine dipstick was read after one minute for nitrites and two minutes for leukocytes. Urine culture was done on cled agar and incubated at 37˚C aerobically for 24 hours, then bacterial identification was made on the cultural and biochemical traits (API 2OE gallery, biomerieux) following overnight incubation at 37˚C. According to the clinical laboratory standards institute guidelines (CLSI, 2013), antimicrobial susceptibility tests were done on Mueller-Hinton agar incubated at 37˚C aerobically for 24 hours using Kirby Bauer disk diffusion method. The results of the cytobacteriological examination of urine were taken 72 hours after the culture except the results of antimicrobial susceptibility tests, considered less important for our study. For the analysis of the results, the sensitivity, the specificity, the predictive values (positive predictive value and negative predictive value), the youden index, the proportion of the correctly classified subjects and the likelihood ratio (positive likelihood ratio and ratio negative likelihood) were calculated. Excel software under Windows 2007 was used for the percentage distribution of bacteria. All procedures herein were approved by the Research Ethics Committee of the Higher Institute of Medical Technology of Lubumbashi, with participants giving informed consents before entering the study.

Six hundred urine samples were analyzed by both methods. Of the 135 cases of urinary tract infections diagnosed by the cytobacteriological examination of urine, five were dipstick negative. Of the 175 positive dipstick cases, 45 were negative for cytobacteriological examination of urine.

1) Contingency table

TP = true positives, TN = True negatives, FP = False positives, FN = False negatives, Test (+) = positive test, Test (−) = negative test.

2) Calculation of tools to estimate the effectiveness of the urine dipstick

a) Calculation of sensitivity and specificity

i) Sensitivity (Se)

Se = TP TP + FN = 130 135 = 0.96 = 96 %

ii) Specificity (Sp)

Sp = TN TN + FP = 420 465 = 0.9 = 90 %

It is, therefore, a sensitive and specific test

b) Calculation of predictive values

i) Positive predictive value (PPV)

PPV = TP TP + FP = 130 175 = 0.74 = 74 %

ii) Negative predictive value (NPV)

NPV = TN TN + FN = 420 425 = 0.988 = 98.8 %

In our study: the positive predictive value of the urine dipstick test is the probability that a subject will actually be infected if the result is positive. The negative predictive value is the probability that, for a subject, the urine is actually sterile if the result is negative.

c) Youden Index (J)

The Youden index (J) is a measure of the accuracy of the diagnostic method. It depends on the specificity and sensitivity of the test but not on the prevalence of the disease.

J = Se + Sp − 1

J = 0. 96 + 0. 9 − 1 = 0. 86

The youden index varies from (−1) to (+1), if J ≤ 0; the test has no informational value.

The test is even better than the youden index is close to 1, in our study J = 0.86.

d) The proportion of correctly classified subjects (CC)

CC = TP + TN Total = 130 + 420 600 = 0.916 = 91.6 %

i.e., in the right category; the number of true positives and true negatives relative to the size of the sample studied.

e) Likelihood ratio (LR)

i) Positive likelihood ratio (LR+)

LR + = Se 1 − Sp = 0.96 1 − 0.9 = 9.6

The positive likelihood ratio measures the likelihood of having a positive test if one is ill and varies from 0 to infinity; The higher it is, the greater the “diagnostic gain” is important.

- LR+ = 1 does not contribute to the diagnosis

- 1 < LR+ ≤ 10 minor contribution to the diagnosis

- LR+ > 10 important contribution to the diagnosis

Thus the urine dipstick has a minor contribution to the diagnosis because the positive likelihood ratio found is 9.6, so a subject at 9.6 is more likely to have a positive test if he has an infection than if he does not have.

ii) Negative likelihood ratio (LR-)

LR − = 1 − Se Sp = 1 − 0.96 0.9 = 0.04

The negative likelihood ratio measures the likelihood of having a negative test if one is not sick. The closer it is to zero, the more it excludes the diagnosis. The subject, therefore, has very little chance of having a positive test if he has no infection (

In undertaking this study, we set ourselves a general goal of evaluating a screening test for urinary tract infection compared to the reference method; cytobacteriological examination of urine finally to promote the realization of the dipstick before any cytobacteriological study of urine. The performance of a test measures its capacity to highlight what we are looking for: the sensitivity and specificity express the capacity of the test to highlight an existing urinary infection, proven by a reference method, without much false negative (sensitivity) or false positives (specificity). Sensitivity reflects his ability not to let the patients go. An

80% sensitive test detects 8 out of 10 patients; in our study, the urine dipstick is 96% sensitive, i.e., it detects 96 patients out of 100. The causes of false negative results of nitrite, that is to say, the associated factors that can produce erroneous results are diuretics, nitrate deficiency in the diet, bacteriuria due to a low concentration of microorganism, infections with gram + bacteria (Staphylococcus saprophyticus, enterococci) or Pseudomonas aeruginosa, Acinetobacter spp. [

The urine dipstick is a test of elimination, by its very high sensitivity (96%), its very high negative predictive value (98.8%) and its negative likelihood ratio close to 0 is 0.04, if the urine dipstick is negative, we are sure that there is no infection and it is not necessary to perform a cytobacteriological examination of urine, i.e. if the dipstick does not detect nitrite and leucocyte, the diagnosis of urinary infection becomes highly unlikely (<2% probability). On the other hand, its positive predictive value is 74%, if the result of the dipstick is positive, the bacteriological culture and the antibiogram should be indicated in this case, in addition to the urine dipstick so as to be able to perform the correct therapeutic choice.

Undeclared.

All authors contributed identically to the different phases of the research.

Bakadia, B.M., Babidi, B.L., Mutoba, T.F., Mbang, M.P., Ndaya, K.A., Biampata, M.J. and Kasamba, I.E. (2018) Evaluation of the Effectiveness of Urine Dipstick in the Screening of Urinary Infection in Relation to the Reference Method: The Cytobacteriological Examination of Urine. Open Access Library Journal, 5: e4790. https://doi.org/10.4236/oalib.1104790