|Year : 2020 | Volume
| Issue : 1 | Page : 61-64
The utility of urinary dipstick in the diagnosis of urinary tract infection in children
Zuhair Mahdi Al-Musawi1, Qahtan Mohammed Ali Al-Obaidy2, Zaynab Hazim Husein3
1 Department of Pediatric, College of Medicine, University of Karbala, Karbala, Iraq
2 Department of Nephrology, Karbala Teaching Hospital for Pediatric, Karbala, Iraq
3 Department of Pediatric, Karbala Teaching Hospital for Pediatric, Karbala, Iraq
|Date of Submission||22-Dec-2019|
|Date of Acceptance||01-Feb-2020|
|Date of Web Publication||17-Mar-2020|
Dr. Zuhair Mahdi Al-Musawi
College of Medicine, University of Karbala, Karbala
Source of Support: None, Conflict of Interest: None
Background: Urinary tract infection (UTI) is frequent in children and may have significant adverse effects, especially for young children. Objective: The objective was to assess the sensitivity and specificity of pyuria, leukocyte esterase, and nitrite test in the diagnosis of UTI and whether they can be used as an alternative to the conventional culture, which is expensive and needs more time for the result to be obtained. Methods: This is a cross-sectional study in which 143 patients were prospectively studied in Kerbela teaching hospital for children, who were suspected to have UTI and did not receive antibiotics for at least a week. Urine samples were collected using urine catheter for children who are not toilet trained and midstream urine for older children. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were measured for nitrite, leukocyte esterase, and pyuria. Results: There was a highly significant association between the positive results of urine dipstick (nitrite test and leukocyte esterase test) and microscopic (examination for pyuria) and the positive results of urine culture (P < 0.001). There were no significant differences between dipstick (nitrate test and leukocyte esterase) and pyuria at sensitivity, specificity, PPVs, and NPVs (P = 0.514, 0.706, 0.232, and 0.414, respectively). Conclusions: The dipstick tests had no significantly different results compared with examination for pyuria and urine culture in the detection of UTIs. Escherichia coli is the most common isolated organism, and it is sensitive mainly to third-generation cephalosporin and amikacin.
Keywords: Escherichia coli, pyuria, urinary tract infection
|How to cite this article:|
Al-Musawi ZM, Ali Al-Obaidy QM, Husein ZH. The utility of urinary dipstick in the diagnosis of urinary tract infection in children. Biomed Biotechnol Res J 2020;4:61-4
|How to cite this URL:|
Al-Musawi ZM, Ali Al-Obaidy QM, Husein ZH. The utility of urinary dipstick in the diagnosis of urinary tract infection in children. Biomed Biotechnol Res J [serial online] 2020 [cited 2020 Jul 8];4:61-4. Available from: http://www.bmbtrj.org/text.asp?2020/4/1/61/280866
| Introduction|| |
Urinary tract infection (UTI) is an infection of any portion of your urinary system (kidney, ureter, bladder, and urethra).
UTI is frequent in children (approximately 2% of boys and 8% of girls experience at least 1 UTI episode by 10 years of age) and may have significant complications, especially for little children. In addition, it has been shown that UTIs with fever in young children increase the probability of kidney involvement and are associated with an increased risk of underlying kidney or bladder abnormalities and later risk of renal scarring. Kidney scarring is considered as a risk for long-term morbidity (hypertension, chronic kidney disease, preeclampsia), though much of this has now been shown to be related to previously presented intrinsic renal disease. Thus, it is clear that an appropriate, reliable diagnosis of UTI in children is mandatory.
Rapid urine tests (also known as a dipstick or macroscopic urinalysis) are still beneficial for the diagnosis of UTI. The nitrite test measures the conversion of nutritional nitrate to nitrite by Gram-negative bacteria. A positive nitrite test makes UTI very likely, but the test may be falsely negative if the bladder is emptied recurrently or if an organism that does not metabolize nitrate (including all Gram-positive organisms) is the cause of infection. The leukocyte esterase test is an indirect measurement of pyuria and, therefore, could be falsely negative when leukocytes are present in low concentration. Microscopic urinalysis is important to determine whether there are leukocytes in the urine, which is a sensitive marker of inflammation associated with infection.
Aim of the study
The objective was to assess the sensitivity and specificity of pyuria, leukocyte esterase, and nitrite test in the diagnosis of UTI and whether they can be used as an alternative to the conventional culture which is expensive and needs more time for the result to be obtained.
The study protocol was approved by the Ethical Committee in the Karbala Health Directorate.
| Methods|| |
This is a cross-sectional study in which 143 patients were prospectively studied in Kerbela teaching hospital for children between January 2017 and January 2018. The age of studied patients was few days to 13 years. The patients did not receive antibiotics for at least a week. The studied patients were presented with one or more of the following symptoms: fever, dysuria, frequency, urgency, enuresis nocturnal or diurnal, dribbling, flank pain, suprapubic pain, vomiting, and hematuria. The study protocol was approved by the Ethical Committee in the Karbala Health Directorate. In addition, verbal approval was taken from the patients and/or their parents before taking the sample.
Urine sampling was done according to the age of the patients, for the patients who were not toilet trained, urine was collected using a urine catheter that was inserted by nephrology department medical personals after the agreement of their parents. While for older children, a fresh midstream urine sample was obtained.
A urine sample was submitted to urinalysis, urine culture, and sensitivity. Urinalysis includes direct microscopic examination which is useful to determine whether there are white blood cells (WBCs) in the urine (a sensitive indicator of inflammation associated with infection). The finding of ≥5 WBCs per high-power field was considered abnormal. Nitrite test by rapid dipstick measure the conversion of dietary nitrate to nitrite by Gram-negative bacteria, a positive test makes UTI very likely. Cultures were considered contaminated if more than one organism or nonpathogens (Acinetobacter species, Candida, Staphylococcus aureus eus etc.) were isolated. Cases with negative cultures were used as control.
Statistical Package for the Social Sciences version 21 (GraphPad Software, San Diego, California, USA) was applied for the statistical analysis of the data. Chi-square test was used to compare the two categorical variables. P < 0.05 was considered to indicate the statistical significance and was highly significant if P < 0.001.
| Results|| |
A total of 143 urine specimens were submitted for urine examination and bacterial culture in patients with suspicion of UTI, and their age ranged from 7 days to 13 years, with most of the patients in the age ≥1 year (110 of 143 patients) [Table 1]. Of 143 patients, 75 (52%) were female and 68 (48%) were male [Figure 1].
The sterile culture (no growth) was observed in 45 specimens and positive culture in 98 specimens. Among total culture-positive cases, 67 specimens show growth of Escherichia More Details coli, 27 specimens show nonspecific Gram-negative bacilli, two specimens with Proteus mirabilis spp., and two specimens Pseudomonas aeruginosa spp. [Table 2].
There was a highly significant association between the positive results of urine dipstick of nitrite test, leukocyte esterase test, and microscopic examination for pyuria and the positive results of urine culture (P < 0.001). Furthermore, there was a highly significant association between the negative results of urine dipstick of nitrite test, leukocyte esterase test, and microscopic examination for pyuria and the negative results of urine culture (P < 0.001) [Table 3].
|Table 3: Correlation of nitrite, leukocyte esterase, and urinalysis with urine culture results|
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There were no significant differences between dipstick (nitrate test and leukocyte esterase) and pyuria (by direct microscope) at sensitivity, specificity, positive predictive values (PPV), and negative predictive values (NPV) (P = 0.514, 0.706, 0.232, and 0.414, respectively) [Table 4].
|Table 4: Sensitivity, specificity, predictive values of dipstick and pyuria (Pus cell detected by direct microscope)|
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The result shows that amikacin was the most sensitive antibiotic for E. coli [Figure 2].
|Figure 2: Frequency of antimicrobial sensitivity and resistance among Escherichia coli|
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| Discussion|| |
Dipstick urine analysis and direct microscopy are the most popular tests used in patients with suspected UTI, which are fast, inexpensive and require little technical experience.
The present study showed that the nitrite test has a specificity of 95.5% while its sensitivity was 67.3%, the PPV and NPV values for nitrite test were 97% and 56.6%, respectively. This result agrees with other previous studies: the study by Yildirim et al. found that the sensitivity and specificity for nitrite test were 61.7% and 96.9%, respectively, and the PPV for nitrite was 95.4%; the study by Mohamed  in Karbala found that sensitivity for nitrite test was 39.3%, whereas specificity and PPV were 87.6% and 74%, respectively; and the study by Carias et al. found that the sensitivity for the nitrite test was 78.6%. While the disagreement with a study conducted by Fernandes et al. reported that sensitivity was 47.37% which is lower than our study, While specificity was 93.4%, PPV was 81.82%, and the NPV was 75.61% was higher than our study.
In a recent meta-analysis, the sensitivity of the nitrite test was 45%–60%, whereas the specificity of the nitrite test was higher (85%–98%). The PPV of the nitrite test has been reported to be nearly 96%, which seems to be similar to our study. This difference may be due to different population samples for these studies (high-risk population, gender, and age) or because of the different brands of strips used for dipstick urinalysis. It may also be due to the improper techniques for collection or transportation of urine samples to the laboratory, allowing the colonizing bacteria to multiply, which result in false-positive nitrite test., Furthermore, a dipstick nitrite test is highly sensitive and specific when properly used in the first-morning urine sample, because bladder should incubate the organism at least 4 h to convert nitrate to nitrite, so random specimens collected at any time or urine from draining catheters do not show good correlation between significant bacteriuria and nitrite test. False-negative results may be due to low pH (<6), ascorbic acid, or urobilinogen.
In the current study, the sensitivity of leukocyte esterase test was 74.4% and specificity was 97.7% which are higher than that of the values reported by Fernandes et al., where the sensitivity and PPV of urinary dipstick test for leukocyte esterase alone, when compared to urine culture in the diagnosis of UTI, were 42.11% and 50%, respectively, while specificity and NPV were 75.76% and 69.44%, respectively. In contrast, Sharief et al. found that the sensitivity for leukocyte esterase was higher (100%) and specificity was lower (78.3%) and PPV and negative predictive were 13.9% and 100%, respectively.
A large meta-analysis study  shows that the sensitivity of the urine dipstick test for leukocyte esterase was in general, slightly higher than for the dipstick test for nitrites (48%–86%), while the specificity was slightly lower (17%–93%).
The differences between studies might be related to the degree of WBC in urine, the enzyme content of immature leukocyte or both.
The sensitivity and PPV of urine pyuria were 84.6% and 89.2%, respectively, while specificity and NPV were 77.7% and 70%, which agree with the previous study of Mohamed which shows higher sensitivity and specificity of 95.7% and 99.2%, respectively. Fernandes et al. found the sensitivity, specificity, PPV, and NPV of urine microscopy were 73.6%, 50%, 45.9%, and 76.7%, respectively.
In a meta-analysis study by Williams et al., the sensitivity of pyuria in diagnosis UTI as compared with positive bacterial urine culture was higher than urinary dipstick, but the specificity was lower 74% (67–80) and 86% (82–90), respectively. This disparity in the study results may be due to laboratory subjective error, as more than one person usually examine the urine sample by a microscope or due to improper storage of the urine sample.
Among all positive urine culture (n = 98) in the present study, we found that the most common organism isolated was E. coli (n = 67), then Klebsiella (n = 2) and Proteus (n = 2) which was similar to the results observed in other previous studies by Mazed et al., Sharma et al., and Taneja et al.,,
The present study is also in line with Al-Musawi, in which E. coli was the most common organism isolated, while other organisms such as Staphylococcus aureus, Streptococcus, and Enterobacter were also isolated, this may be related to the usage of urine bag for urine collection which is liable for contamination and bacterial overgrowth, while in the current study, urine catheter and midstream urine sampling were the methods used for urine collection.
In our study, the most sensitive antibiotic for E. coli was third-generation cephalosporin and amikacin as shown in [Figure 2], while these bacteria were resistant to important medications such as trimethoprim, sulfamethoxazole, and amoxicillin used in conventional UTI in update recommendation. This could be due to the wide improper use of these antibiotics which resulted in the emergence of a new generation of resistant bacteria to these antibiotics.
| Conclusions|| |
The dipstick (nitrite test and leukocyte esterase test) and microscopic (examination for pyuria) and urine culture had the same result in detect UTI. Nitrite test has a specificity of 95.5% and a sensitivity of 67.3%. Leukocyte esterase has a specificity of 97.7% and a sensitivity of 74.4%, which not have a significant difference when compared with specificity and sensitivity of pyuria. Both tests (nitrite and leukocyte esterase) are inexpensive, rapid, and available for the early detection of UTI pending the result of culture and sensitivity.
E. coli is the most common isolated organism, and it is sensitive mainly to third-generation cephalosporin and amikacin.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]