Can routine automated urinalysis reduce culture requests?

Clinical Biochemistry xxx (2013) xxx–xxx

CLB-08429; No. of pages: 5; 4C:

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Clinical Biochemistry

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Can routine automated urinalysis reduce culture requests?

Damla Kayalp, Kubra Dogan, Gozde Ceylan, Mehmet Senes, Dogan Yucel ⁎Department of Medical Biochemistry, Ankara Training and Research Hospital, Ministry of Health, Cebeci, Ankara 06340, Turkey

Abbreviations: CFU, colony forming units; DOR, diagnofield; LR, likelihood ratio; LE, leukocyte esterase; NPV, negitive predictive value; ROC, receiver operating characterisWBC, white blood cell.⁎ Corresponding author at: Ankara Training and Resear

Cebeci, Ankara 06340, Turkey.E-mail address: [email protected] (D. Yucel).

0009-9120/$ – see front matter © 2013 The Canadian Shttp://dx.doi.org/10.1016/j.clinbiochem.2013.06.015

Please cite this article as: Kayalp D, et al, C10.1016/j.clinbiochem.2013.06.015

a b s t r a c t
a r t i c l e i n f o
Article history:
Received 3 March 2013Received in revised form 13 June 2013Accepted 14 June 2013Available online xxxx
Keywords:UrinalysisUrinary tract infectionBacteriuriaCultureData miningEvidence-based laboratory medicineRational test requesting

Objectives: There are a substantial number of unnecessary urine culture requests. We aimed to investi-gate whether urine dipstick and microscopy results could accurately rule out urinary tract infection (UTI)without urine culture.

Design and methods: The study included a total of 32 998 patients (11 928 men and 21 070 women,mean age: 39 ± 32 years) with a preliminary diagnosis of UTI and both urinalysis and urinary culturewere requested. All urine cultures were retrospectively reviewed; association of culture positivity with a pos-itive urinalysis result for leukocyte esterase (LE) and nitrite in chemical analysis and pyuria (WBC) and bac-teriuria in microscopy was determined. Diagnostic performance of urinalysis parameters for detection of UTIwas evaluated.

Results: In total, 758 (2.3%) patients were positive by urine culture. Out of these culture positive samples,ratios of positive dipstick results for LE and nitrite were 71.0% (n = 538) and 17.7% (n = 134), respectively.The positive microscopy results for WBC and bacteria were 68.2% (n = 517) and 78.8% (n = 597), respec-tively. Negative predictive values for LE, nitrite, bacteriuria and WBC were very close to 100%.

Conclusions: Most of the samples have no or insignificant bacterial growth. Urine dipstick and microsco-py can accurately rule out UTI. Automated urinalysis is a practicable and faster screening test which may pre-vent unnecessary culture requests for majority of patients.

© 2013 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Introduction

Urinary tract infection (UTI) which is one of the most common in-fections diagnosed in the clinical laboratories is also one of the leadingcauses of nosocomial infections [1]. UTI is themostly seen bacterial in-fection in young women and in the elderly. Most women get at leastone UTI in their lifetime. Themost frequently determinedmicroorgan-isms in UTI are gram negative enteric bacteria and the most commongrowing bacteria in urine culture is Escherichia coli. Contamination isanother commonly seen reason that causes positive culture resultswith a ratio of 29%–32% [2,3]. Althoughmedical history and symptomsare sufficient for diagnosis, culture should be made for precise diag-nosis and bacterial identification. A precise diagnosis prevents unnec-essary use of antibiotics and helps to distinguish patients requiringfurther examination. On the other hand, urine culture is expensiveand time consuming. By standard microbiological techniques, atleast 18 h is necessary for detection of bacterial growth on culture

stic odds ratio; hpf, high powerative predictive value; PPV, pos-tics; UTI, urinary tract infection;

ch Hospital, Ulucanlar Caddesi,

ociety of Clinical Chemists. Publishe

an routine automated urinaly

media. This means that the diagnosis is uncertain for the first 18–48 h after presentation which leads to delayed or inappropriate treat-ment [4]. A fast, reliable, easy, inexpensive and sensitive screening testis needed to begin treatment as early as possible [5].

On the other hand, there are studies reporting unnecessary urineculture requests in the literature [3,6]. An effective screening test be-fore culture requests can prevent unnecessary spending of time andexpenditure and avoid unnecessary drug treatment, resulting in thesaving of costs [7]. The investigation of leukocyte esterase (LE) and ni-trite with urine strips andmicroscopic investigation of pyuria and bac-teriuria are suitable for this purpose.

The aims of this study were to investigate the relationship be-tween the results of infection related parameters of routine urinalysisand culture results for early diagnosis and to determine the value ofurinalysis for prediction of positive culture results.

Materials and methods

We searched the electronic database of Ankara Training and Re-search Hospital which is a tertiary central hospital with 630 beds, be-tween September 2009 and August 2010. Approximately 150 000urinalyses are requested per year while the majority of these requestsis from outpatients and emergency patients (N90%). In the indicatedtime period of our study, 88 325 requests were from outpatients,

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2 D. Kayalp et al. / Clinical Biochemistry xxx (2013) xxx–xxx

53 027 were from emergency patients and 5996 were from services.The reasons for urine test requests were screening, pre-hospitalizationor pre-surgery testing, and symptomatic and emergency appeals.

The results of patients who had simultaneous requests for both uri-nalysis and urine culture were examined. We collected 32 998 patients[11 928 men (36.3%) and 21 070 women (63.7%)] with a mean age of39 ± 32 years (age ranges from 0 to 95 years); 15.5% were 0–1 yearold (0.5 ± 0.5 year), 63.1% were 2–17 (6.7 ± 4.1 years), 18.9% were18–69 (49.8 ± 16.4 years) and 2.4% were ≥70 years old (78.2 ±5.5 years). The Institutional Review Board of the hospital approvedthe study.

As part of our current routine protocol, patientswere asked towipetheir external genitalia before urinating. Then spot mid-stream urinesamples were collected into two evacuated sterile plastic containers(Vacutest Kima s.r.l., Arzergrande, Italy), one for urinalysis and theother for culture. A sterile urine collection bag was used for collectionof urine specimens from newborns and infants. In our hospital, urinebag specimens were not accepted for urine culture. Catheter andFoley catheter samples could be used for culture but these sampleswere excluded from the study. Contaminated samples were not in-cluded in the study as well. After urine culture inoculation, urinalysiswas performed.

We used an automated urinalysis system for dipstick and micro-scopic testing [LabUMat with UriSed (77 Elektronika Kft, Budapest,Hungary)]. Ten milliliters of each sample was used for routine urinal-ysis. The LabStrip Urinalysis U11 Plus test strips (Analyticon Biotech-nologies AG, Lichtenfels, Germany) were used for the dipstick testing.The parameters assessed were LE, nitrite and ascorbic acid by the teststrips and white blood cells (WBCs) and bacteria by microscopy. WBCand bacteria were counted per high-power field (hpf, 400× magnifi-cation), but bacteria counts were reported semiquantitatively as neg-ative, (1+), (2+), and (3+) (negative: 0–12; 1+: 13–32; 2+: 33–100; 3+: ≥101 cells/hpf). Counts in hpf correspond to particle/μL×6.25. Microscopy was regarded positive for pyuria when the num-ber of WBC was N5/hpf.

Urinalysis was completed within 1 h after receiving samples. Be-cause the UriSed can display entire microscopic images of 15 fieldswith a high resolution comparable with manual microscopy, and itcan allow corrections by the user, we do not have to resort to manualmicroscopy in routine studies. Low and high levels of quality controlmaterials (Quantimetrix Dip & Spin Urine Dipstick/Microscopics Con-trols) were used for internal quality control.Within-run and between-day precisions (n = 21 for both)were determined forWBC. For bacte-ria, the within-run precision (n = 21) was determined by analyzingfour in-house pooled samples. One of the pools was negative for bac-teria and the others were positive having different counts of bacteriaas 1+, 2+, and 3+. Within-run precisions (repeatability) of low(0–4 WBC/hpf) and high (4–16 WBC/hpf) WBC levels were 33.4%and 12.5%, respectively. Between-run precisions of low and high levelsofWBCwere 29.9% and 21.4%, respectively.Within-run CV%was 22.1%at 0–12 bacteria/hpf counts, 6.54% at 12–32 bacteria/hpf, 2.13% at 32–100 bacteria/hpf and 5.51% for ≥101 bacteria/hpf.

Urine samples were cultured by application of 10 μL on eosin meth-ylene blue agar and blood agar plates (Or-Bak, Cagdas 06 HealthcareServices, Ankara, Turkey). Cultures were incubated at 37 °C for 24 hand VITEK 2 (Biomerieux, Marcy L'etoile, France) was used for identifi-cation. Bacterial counts were expressed as numbers of colony formingunits (CFU) per mL. Samples were considered positive if either a pureof predominant culture of N105 CFU/mL, two organisms in similarproportions at N105 CFU/mL or 104–105 CFU/mL of a gram negative or-ganism or two organisms where the gram negative clearly predomi-nates. When three or more different colonies without a dominantspecies had grown (mixed flora), the urinewas considered contaminat-ed (mixed growth) and rejected.

Culture was used as the reference for determining the performanceof the dipstick andmicroscopy data. Diagnostic sensitivities, specificities,

Please cite this article as: Kayalp D, et al, Can routine automated urinaly10.1016/j.clinbiochem.2013.06.015

positive and negative predictive values (PPV and NPV), likelihood ra-tios (LR+ and LR−) and diagnostic odds ratios (DORs) of dipstickand microscopy parameters were calculated. Spearman correlationbetween parameters and ROC analysis for WBC and LE were per-formed by SPSS® for Windows ver. 17 (SPSS Inc., Chicago, IL, USA).

Results

In total, 32 998 urine samples were studied. Of these, 32 240(97.7%) cultures were negative while substantial microbiologicalgrowth was detected in 758 (2.3%) specimens. Of 758 patients withmicrobial growth, 510 (67.3%) were female and E. coli was the mostcommonly cultured pathogen with a percentage of 60.4% (n = 458).When cultured pathogens are assessed, 17.7% (n = 134) of specimenswere found nitrite positive, whereas E. coli had the highest percentageof 78.4% (n = 105). Two different pathogens had grown concomitant-ly in 4.9% of specimens (n = 37). Growth of three or more differentcolonies was considered contaminated (n = 2639; 7.4%) and exclud-ed from the study.

Microscopic examination of urine sediment from the 758 speci-mens revealed that 517 specimens (68.2%) had ≥5 WBC per high-power field. Using the bacteria count, bacteria were determined in597 samples (76.4%). Dipstick analysis showed 538 LE (71.0%) and134 nitrite (17.7%) positive results in culture positive specimens. Theresults of the dipstick test for LE and nitrite and microscopic exami-nation for WBC and bacteriuria were compared and the sensitivity,specificity, PPV, NPV and DOR of the test strips andmicroscopic exam-ination results were assessed. Bacteriuria had the highest sensitivityand specificity (78.8% and 97.8%, respectively) which was followedby LE with a sensitivity of 71.0%. The specificity of all parameterswere N80%. When the urinalysis result was positive for any one ofLE, nitrite, WBC or bacteria, the sensitivity for UTI was increased to79.6%. The PPV of a positive bacteriuria result was 45.4% with a NPVof 99.5%. Other tests had lower positive and negative predictive valuesthan bacteriuria (Table 1). The area under the curve (AUC) was 0.910(95% CI = 0.895–0.924) for the WBC count and 0.970 (0.962–0.978)for the LE in the ROC analysis in which culture results were taken asthe reference for UTI (Fig. 1). Since the presence of leukocytes is cru-cial in the detection of UTI, the sensitivity and specificity were evalu-ated with different cut-off values to obtain a low number of falsenegatives. When a cut-off value of 3 WBC/hpf was selected, the sensi-tivity increased to 81.4% (95% CI = 78.3–84.0) but specificity de-creased to 86.0% (95% CI = 85.7–86.3).

When the population was divided into different age groups, themost sensitive tests were LE for ages 0–1 and bacteriuria for age groupsof 2–17 years, 18–69 years and ≥70 years (63.7%, 72.6%, 91.8% and86.4%, respectively). The most specific parameter was bacteriuria in allgroups (Table 1).

In the correlation analysis, a weak correlation was found betweennitrite and LE (r = 0.077; P = 0.033), and between LE and bacteria(r = 0.089; P = 0.014), but a moderate correlation was found be-tween bacteria and nitrite (r = 0.343; P b 0.001). A relatively highcorrelation was found between LE and microscopic WBC count(r = 0.664; P b 0.001).

Ascorbic acid may negatively interfere with the nitrite and LE re-sults that may cause false negative results even in the presence of bac-teriuria or pyuria. In culture positive samples, ascorbic acid was foundto be positive where nitrite and LE were negative with a ratio of 7.2%(n = 45) and 11.4% (n = 25), respectively.

Discussion

In this retrospective study, we compared the results of automatedurinalysis with the results of urine culture for UTI. Our results showedthat only 2.3% of the culture requested patients had positive cultureresults which revealed an excessively high unnecessary urine culture




Table 1Diagnostic performance of test strips and sediment microscopy in all subjects and different age groups.

Test Sensitivity (95% CI) Specificity (95% CI) PPV (95% CI) NPV (95% CI) LR+ (95% CI) LR− (95% CI) DOR

LEAll 71.0 (67.6–74.2) 83.6 (83.2–84.2) 9.2 (8.5–10.0) 99.3 (99.1–99.4) 4.3 (4.1–4.6) 0.347 (0.310–0.388) 12.50–1 63.7 (53.6–73.0) 68.8 (67.5–70.0) 4.0 (3.1–5.0) 98.9 (98.5–99.3) 2.0 (1.8–2.4) 0.528 (0.408–0.683) 3.92–17 65.7 (58.7–72.2) 88.6 (88.1–89.0) 5.3 (4.4–6.3) 99.6 (99.5–99.7) 5.7 (5.2–6.4) 0.388 (0.320–0.469) 14.818–69 77.0 (71.3–82.0) 80.8 (79.8–81.8) 14.6 (12.8–16.6) 98.8 (98.5–99.1) 4.0 (3.7–4.4) 0.285 (0.228–0.357) 14.1≥70 72.4 (65.6–78.5) 66.0 (62.0–69.8) 42.1 (36.8–47.5) 87.5 (84.0–90.4) 2.1 (1.8–2.5) 0.419 (0.332–0.528) 5.1

NitriteAll 17.7 (15.0–20.6) 90.1 (89.7–90.4) 4.0 (3.4–4.7) 97.9 (97.7–98.2) 1.8 (1.5–2.08) 0.914 (0.884–0.945) 2.00–1 6.9 (2.8–13.6) 90.1 (89.2–90.9) 1.4 (0.6–2.8) 98.0 (97.5–98.3) 0.7 (0.3–1.4) 1.034 (0.980–1.091) 0.72–17 21.9 (16.4–28.3) 97.3 (97.1–97.5) 7.4 (5.4–9.8) 99.2 (99.1–99.3) 8.2 (6.2–10.7) 0.803 (0.746–0.864) 10.218–69 19.9 (15.2–25.4) 68.1 (66.9–69.2) 2.6 (1.9–3.4) 95.2 (94.5–95.8) 0.6 (0.5–0.8) 1.177 (1.104–1.254) 0.5≥70 16.1 (11.3–21.9) 60.1 (56.0–64.1) 12.1 (8.4–16.7) 67.7 (63.5–71.7) 0.4 (0.3–0.6) 1.395(1.276–1.527) 0.3

BacteriuriaAll 78.8 (75.7–81.6) 97.8 (97.6–97.9) 45.4 (42.7–48.1) 99.5 (99.4–99.6) 35.3 (32.6–38.3) 0.217 (0.189–0.249) 162.60–1 43.1 (33.4–53.3) 98.0 (97.5–98.3) 30.1 (22.8–38.3) 98.8 (98.5–99.1) 21.3 (15.9–28.5) 0.580 (0.490–0.687) 36.62–17 72.6 (65.9–78.7) 98.3 (98.2–98.5) 29.8 (25.8–34.1) 99.7 (99.6–99.8) 43.6 (38.1–49.9) 0.278 (0.222–0.349) 156.618–69 91.8 (87.7–94.9) 97.0 (96.5–97.4) 56.4 (51.4–61.2) 99.6 (99.4–99.8) 30.2 (26.1–35.1) 0.085 (0.056–0.127) 357.5≥70 86.4 (80.9–90.9) 84.4 (81.2–87.2) 65.4 (59.3–71.1) 94.8 (92.5–96.5) 5.5 (4.5–6.7) 0.161 (0.113–0.229) 34.4

WBCAll 68.2 (64.8–71.5) 87.8 (87.5–88.2) 11.7 (10.7–12.6) 99.2 (99.0–99.3) 5.6 (5.3–5.9) 0.362 (0.326–0.401) 15.50–1 49.0 (39.0–59.1) 81.9 (80.9–83.0) 5.2 (3.9–6.8) 98.8 (98.4–99.1) 2.7 (2.2–3.3) 0.622 (0.514–0.753) 4.42–17 41.8 (34.9–48.9) 90.3 (89.8–90.7) 4.0 (3.2–4.9) 99.4 (99.3–99.5) 4.3 (3.6–5.1) 0.645 (0.574–0.725) 6.618–69 84.0 (78.9–88.3) 85.6 (84.7–86.5) 20.0 (17.6–22.5) 99.2 (98.9–99.4) 5.8 (5.4–6.3) 0.187 (0.141–0.248) 31.2≥70 84.4 (78.6–89.2) 76.0 (72.3–79.4) 54.6 (48.8–60.2) 93.5 (90.1–95.5) 3.5 (3.0–4.1) 0.205 (0.148–0.284) 17.7

PPV: Positive predictive value; NPV: Negative predictive value; LR+: Positive likelihood ratio; LR−: Negative likelihood ratio; DOR: Diagnostic odds ratio.

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requests. It may be claimed that routine urinalysis could reduce thecosts resulting from superfluous culture requesting.

In patients with suspected UTI, an accurate and instant diagnosis iscrucial for therapeutic approach. In parallel with the clinical examina-tion, collecting an appropriate urine sample for testing the presenceof infection is an important issue. Spot mid-stream urine samplesare collected to minimize the number of contaminated specimensby commensal bacteria because the first voided urine sample is al-ways contaminated by urethral flora in both sexes [8]. In the presentstudy, as part of our routine protocol mid-stream urine samples werecollected and only 758 samples among 32 998 were found culture

Fig. 1. ROC curves for WBC and LE. Dashed line for LE and solid line for WBC. AUC for LEis 0.970 (95% CI: 0.962–0.978) and for WBC is 0.910 (95% CI: 0.895–0.924). AUC: areaunder the curve; SE: standard error; 95% CI: 95% confidence interval.


positive. This shows the excessively high percentage of unnecessaryurine culture requests (i.e., 97.7%). Christenson et al. and Okada etal. also attained high culture negative results with a percentage of82.1% and 80%, respectively [9,10]. Because urinalysis is a relativelyinexpensive screening test in the diagnosis of UTI, requesting urineculture for most of the patients with urine problems causes relativelyhigh unnecessary costs. Urine culture, where no growth or insignifi-cant growth is observed in most of the samples, requires intensive ef-forts and is time-consuming. Therefore this kind of time-consuminganalysis also causes the prolongation of the duration of hospitaliza-tion. Moreover, it delays the treatment procedures and increaseshealth expenditures [6,8].

With regard to microbiological growth, E. coli is found to be themost common uropathogen causing UTI in our study. Ducharme etal. also found that E. coli was the most commonly cultured pathogen(54.5%) [11]. As expected, 65.1% of E. coli positive results were comingfrom female patients.

When culture positive samples were compared with chemical andmicroscopic examination of the sediment, bacteria count and LE werefound as consistent with culture results. Themost sensitive and specif-ic parameter is bacteriuria (78.8% and 97.8%, respectively) which wasfollowed by LE with a high sensitivity of 71.0%. All parameters have aspecificity of N80.0%, whereas WBCs have the highest specificity(87.8%) after bacteriuria. In addition, dipstick results of LE are moresensitive than microscopic results of WBC. As indicated by Kupelianet al., although microscopy is a part of urine analysis in most of the di-agnostic laboratories, dipstick testing has replacedmicroscopy in clin-ical settings [12]. However, diagnostic performance of microscopicWBC count is still high [AUC = 0.910 (CI 95% = 0.895–0.924) inROC analysis]. When the combinations of bacteriuria and LE, bacteri-uria and nitrite, bacteriuria andWBC, andWBC and LE were comparedwith culture, sensitivity was decreased but specificity increased. Forsensitivity, WBC and LE combination had the highest score (66.5%)which was followed by bacteria and nitrite combination (21.9%). Forspecificity, bacteriuria and nitrite combination is found to have thehighest score (100%). While all combinations with bacteriuria had aspecificity of nearly 100%, WBC and LE combination had 95.3%. But ifthe urinalysis results for either LE or nitrite were positive, sensitivity




4 D. Kayalp et al. / Clinical Biochemistry xxx (2013) xxx–xxx

increased up to 73.4%. However, if one of the results for LE, nitrite,WBC or bacteria was positive, sensitivity raised to 80%. Although bac-teria and LE results alone had lower sensitivity, when they wereassessed together, specificity was increased at the expense of sensitiv-ity. In the study by Hughes et al. performed with IRIS 939 UDx, it wasfound that bacteriuria has a sensitivity of 84.6% and a specificity of65.0% which were the best that could be achieved [13]. Although bac-teria results of UriSed were lower than IRIS, specificity was higher. Butthese urinalysis systems have different working techniques. UriSedobtains and records high resolution images of microscopic fields likemanual microscopic sediment analysis while IRIS uses a flow cellaligned in the focal plane of an attachedmicroscope with a video cam-era and obtained microscopic images are classified and quantified byan image analysis software. The discrepancy between two analyticsystemsmay result from this technical difference. In addition, it is pos-sible to increase sensitivity by lowering the cut-off in UriSed. Thuswhen we lowered the WBC cut-off to 3 WBC/hpf, the sensitivity in-creased to 81.4% although specificity decreased to 86%. Since highersensitivity is more useful in screening tests, it can be said that thiscut-off is more reasonable than 5 WBC/hpf for the screening of UTI.

Our results showed that when only bacteria count is considered,sensitivity raised up to 80%. However, combination of two parameterslowers sensitivity but increases specificities up to 100%, with thehighest of bacteria and nitrite combination (100%). According to theEuropean Urinalysis Guideline, the sensitivity and specificity of dip-stick results of LE are both preferred to be about 80–90% [14]. In con-trast, sensitivity is found much lower than expected in some studies[3,11,13]. Although our results are consistent with the specificity re-sults (with the LE specificity of 98.1%), we found a lower LE sensitivityfrom expected. The guideline also emphasizes that, low false negativerates (ideally b10%) in detection of bacteria would identify true neg-ative samples and lowers costs and unnecessary urine cultures [13].Our false negative rate in bacteria was higher (21.2%) than stated inthe guideline, but similar to the study by Christenson et al. in whichfalse negative rate was 25% [9]. Because we included both symptom-atic and asymptomatic patients in our study, false negative rate wasfound higher than expected. If only symptomatic patients were in-cluded, false negative rate would be lower. A relatively recent studyindicates that LE had a higher sensitivity than nitrite, while specificitywas slightly lower [15]. Our results are similar to these findings.

Another important point in chemical urinalysis by dipsticks isascorbic acid interference. In our study false negatives ratios of nitriteand LE were 7.2% and 11.4%, respectively in culture positive andascorbic acid positive patients. However, bacteria and WBC positivitycompensate negative ascorbic acid interference in nitrite and LE.

The predictive value of the test results is important for the pre-testprobability of a disease. In a former study, Bolann et al. reported thatthe ability of LE and nitrite test strips to detect or exclude UTI wascomparable with that of sediment microscopy [16]. However, bacteri-uria gave the highest PPV (45.4%) in our study. The NPVs are foundmuch higher than PPVs, with the highest of bacteriuria by 99.5% andLE by 99.3%. Ditchburn et al. also found higher NPVs than PPVs of LE(90% vs. 66%) [17]. When bacteriuria and nitrite, LE and WBC areconsidered together, all the PPVs are found to increase. Bacteriuriaand nitrite combination had the highest PPV (79.4%). Our results aresupported with a study by Okada et al., in which a low PPV and ahigh NPV of bacteriuria were determined (63.0% and 90.7%, respective-ly) [10]. Since, (LR+) N10 aids to rule-in and (LR−) b0.1 to rule-out adisease in general, bacteria count is themost effectivemeans for rule-inthe UTI.

When we compared different age groups, the highest sensitivityat 0–1 year was LE and bacteriuria at 2–17 years, 18–69 years and≥70 years. Bacteriuria was the most specific parameter in all agegroups. Our results are consistent with the study by Arinzon et al.,where elderly patients of ages N61 had higher NPVs for LE than for ni-trite [18]. At the age of 0–1 year, LE had the highest NPV. The highest


LR+ for LE, nitrite and bacteriuria was in the group of 2–17 years (5.7,8.2 and 43.6, respectively). LR+ for WBC was highest at 18–69 years(5.8). Bacteriuria had the lowest LR− of 0.085 at the ages of 18–69 years. On the contrary to Mori et al., we found that, the LR+ washigher for the WBC than LE (2.7 vs. 2.0) in children younger than2 years. But when a cut-off value of 10 WBC/hpf was used, Mori etal. described a higher LR+ for WBC than LE [19].

Study limitations

Although the present study was based on a relatively large numberof patients, the retrospective nature of the study prevented us to clas-sify the subjects as symptomatic or asymptomatic. It could be better toseparate symptomatic and asymptomatic patients. In the study ofKoeijers et al. [20], only dipstick nitrite and LE were evaluated in 422symptomatic patients and PPV of positive nitrite result was found as96%; LE results did not improve the diagnostic accuracy. This substan-tially high PPV result for nitrite is reasonable because the study isperformed in only symptomatic males. Another important limitationwas high imprecision of WBC and bacteria, especially in low-level con-trols. But the imprecision is reasonable in high-level controls. Of course,this high imprecision should be considered during the interpretation.

Conclusions

Urinalysis may accurately rule out UTI in the majority of subjects.Also, Little et al. indicated that dipstick results can improve diagnosticprecision but poorly rule out infection [21,22]. While bacteriuria hasthe highest LR+ and DOR, combined evaluation of dipstick and mi-croscopic tests gives better results for the lack of UTI. The urinalysisis an essential screening test in determining the presence of UTI. Interms of evidence-based laboratory medicine, when UTI is suspectedthe first step should be routine urinalysis instead of urine culture. Cul-ture might be necessary depending on the result of urinalysis.

Acknowledgments

We thank the Department of Medical Microbiology of Ankara Train-ing and Research Hospital for close collaboration during the study.

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Can routine automated urinalysis reduce culture requests?