Dysuria is a common presenting complaint of women and urinalysis is a valuable tool in the initial evaluation of this
presentation. Clinicians need to be aware that pyuria is the best determinate of bacteriuria requiring therapy and
that values significant for infection differ depending on the method of analysis. A hemocytometer yields a value of
≥ 10 WBC/ mm3
significant for bacteriuria, while manual microscopy studies show ≥ 8 WBC/high-power field
reliably predicts a positive urine culture. In cases of uncomplicated symptomatic urinary tract infection, a positive
value for nitrites and leukocyte esterase by urine dipstick can be treated without the need for a urine culture. Automated
urinalysis used widely in large volume laboratories provides more sensitive detection of leukocytes and
bacteria in the urine.With automated microscopy, a value of > 2 WBC/hpf is significant pyuria indicative of inflammation
of the urinary tract. In complicated cases such as pregnancy, recurrent infection or renal involvement,
further evaluation is necessary including manual microscopy and urine culture with sensitivities.
Many studies have evaluated the accuracy of dipstick tests as rapid detectors of bacteriuria and urinary tract infections (UTI). The lack of an adequate explanation for the heterogeneity of the dipstick accuracy stimulates an ongoing debate. The objective of the present meta-analysis was to summarise the available evidence on the diagnostic accuracy of the urine dipstick test, taking into account various pre-defined potential sources of heterogeneity.
Literature from 1990 through 1999 was searched in Medline and Embase, and by reference tracking. Selected publications should be concerned with the diagnosis of bacteriuria or urinary tract infections, investigate the use of dipstick tests for nitrites and/or leukocyte esterase, and present empirical data. A checklist was used to assess methodological quality.
70 publications were included. Accuracy of nitrites was high in pregnant women (Diagnostic Odds Ratio = 165) and elderly people (DOR = 108). Positive predictive values were ≥80% in elderly and in family medicine. Accuracy of leukocyte-esterase was high in studies in urology patients (DOR = 276). Sensitivities were highest in family medicine (86%). Negative predictive values were high in both tests in all patient groups and settings, except for in family medicine. The combination of both test results showed an important increase in sensitivity. Accuracy was high in studies in urology patients (DOR = 52), in children (DOR = 46), and if clinical information was present (DOR = 28). Sensitivity was highest in studies carried out in family medicine (90%). Predictive values of combinations of positive test results were low in all other situations.
Overall, this review demonstrates that the urine dipstick test alone seems to be useful in all populations to exclude the presence of infection if the results of both nitrites and leukocyte-esterase are negative. Sensitivities of the combination of both tests vary between 68 and 88% in different patient groups, but positive test results have to be confirmed. Although the combination of positive test results is very sensitive in family practice, the usefulness of the dipstick test alone to rule in infection remains doubtful, even with high pre-test probabilities.
Dipsticks are one of the most commonly used near-patient tests in primary care, but few clinical or dipstick algorithms have been rigorously developed.
To confirm whether previously documented clinical and dipstick variables and algorithms predict laboratory diagnosis of urinary tract infection (UTI).
Design of study
A total of 434 adult females with suspected lower UTI had bacteriuria assessed using the European Urinalysis Guidelines.
Sixty-six per cent of patients had confirmed UTI. The predictive values of nitrite, leucocyte esterase (+ or greater), and blood (haemolysed trace or greater) were confirmed (independent multivariate odds ratios = 5.6, 3.5, and 2.1 respectively). The previously developed dipstick rule — based on presence of nitrite, or both leucocytes and blood — was moderately sensitive (75%) but less specific (66%; positive predictive value [PPV] 81%, negative predictive value [NPV] 57%). Predictive values were improved by varying the cut-off point: NPV was 76% for all three dipstick results being negative; the PPV was 92% for having nitrite and either blood or leucocyte esterase. Urine offensive smell was not found to be predictive in this sample; for a clinical score using the remaining three predictive clinical features (urine cloudiness, dysuria, and nocturia), NPV was 67% for none of the features, and PPV was 82% for three features.
A clinical score is of limited value in increasing diagnostic precision. Dipstick results can modestly improve diagnostic precision but poorly rule out infection. Clinicians need strategies to take account of poor NPVs.
algorithms, clinical scoring; diagnosis, urinary tract infection; primary care; urinalysis
Suspected urinary tract infection (UTI) is one of the most common presentations in primary care. Systematic reviews have not documented any adequately powered studies in primary care that assess independent predictors of laboratory diagnosis.
To estimate independent clinical and dipstick predictors of infection and to develop clinical decision rules.
Design of study
Validation study of clinical and dipstick findings compared with laboratory testing.
General practices in the south of England.
Laboratory diagnosis of 427 women with suspected UTI was assessed using European urinalysis guidelines. Independent clinical and dipstick predictors of diagnosis were estimated.
UTI was confirmed in 62.5% of women with suspected UTI. Only nitrite, leucocyte esterase (+ or greater), and blood (haemolysed trace or greater) independently predicted diagnosis (adjusted odds ratios 6.36, 4.52, 2.23 respectively). A dipstick decision rule, based on having nitrite, or both leucocytes and blood, was moderately sensitive (77%) and specific (70%); positive predictive value (PPV) was 81% and negative predictive value (NPV) was 65%. Predictive values were improved by varying the cut-off point: NPV was 73% for all three dipstick results being negative, and PPV was 92% for having nitrite and either blood or leucocyte esterase. A clinical decision rule, based on having two of the following: urine cloudiness, offensive smell, and dysuria and/or nocturia of moderate severity, was less sensitive (65%) (specificity 69%; PPV 77%, NPV 54%). NPV was 71% for none of the four clinical features, and the PPV was 84% for three or more features.
Simple decision rules could improve targeting of investigation and treatment. Strategies to use such rules need to take into account limited negative predictive value, which is lower than expected from previous research.
clinical scoring algorithms; diagnosis, urinary tract infection; dipsticks
Urinary tract infection (UTI) is one of the most common sources of infection in children under five. Prompt diagnosis and treatment is important to reduce the risk of renal scarring. Rapid, cost-effective, methods of UTI diagnosis are required as an alternative to culture.
We conducted a systematic review to determine the diagnostic accuracy of rapid tests for detecting UTI in children under five years of age.
The evidence supports the use of dipstick positive for both leukocyte esterase and nitrite (pooled LR+ = 28.2, 95% CI: 17.3, 46.0) or microscopy positive for both pyuria and bacteriuria (pooled LR+ = 37.0, 95% CI: 11.0, 125.9) to rule in UTI. Similarly dipstick negative for both LE and nitrite (Pooled LR- = 0.20, 95% CI: 0.16, 0.26) or microscopy negative for both pyuria and bacteriuria (Pooled LR- = 0.11, 95% CI: 0.05, 0.23) can be used to rule out UTI. A test for glucose showed promise in potty-trained children. However, all studies were over 30 years old. Further evaluation of this test may be useful.
Dipstick negative for both LE and nitrite or microscopic analysis negative for both pyuria and bacteriuria of a clean voided urine, bag, or nappy/pad specimen may reasonably be used to rule out UTI. These patients can then reasonably be excluded from further investigation, without the need for confirmatory culture. Similarly, combinations of positive tests could be used to rule in UTI, and trigger further investigation.
Acute urinary tract infection may be preceded by and active pyelonephritis may be associated with asymptomatic bacteriuria. Treatment of asymptomatic bacteriuria may prevent or arrest active, chronic pyelonephritis and its sequelae. Consequently, there is a need for a reliable and simple screening procedure to detect asymptomatic bacteriuria in large segments of the population.
The reliability and practicability of tests advocated for the detection of bacteriuria, including the new chemical triphenyltetrazolium chloride (T.T.C.) (Uroscreen) test, were evaluated. Reliability was assessed by correlating results of these tests with bacterial counts of tested urines. Significant bacteriuria is defined as the presence of 100,000 or more organisms per ml. of urine.
The T.T.C. (Uroscreen) test was positive in 92.5% of cases of bacteriuria; there were 7.5% false-negative and 2.8% false-positive results. Bacteria on Gram-stained smear were found in 95.5% of the cases of bacteriuria and in 14.6% of those with non-infected urine; pyuria (more than three leukocytes per high-power field), in 60% of those with bacteriuria and in 15.9% of those with presumably non-infected urine. Bacteria were conspicuous in the urinary sediment in 91.1% of cases of bacteriuria and in 3.7% of presumably non-infected urines.
The T.T.C. (Uroscreen) test fulfilled the criteria for a reliable and simple screening procedure. It should be used concomitantly with other screening tests when the urine is examined routinely.
A combination of reagent strip testing and examining urine appearance can be used to screen out noninfected cases before urine specimens are sent to the laboratory. A validation of this method was carried out in a microbiology laboratory using 970 specimens received over a three-week period. When the tests for nitrite, blood and protein on N-Multistix reagent strips (Ames) were all negative in a clear urine then the predictive value for the absence of bacteriuria was 98.5%. Positive strip tests in a turbid urine detected 80.1% of infections. On the basis of these findings it is recommended that general practitioners test the urine samples of all patients with suspected urinary tract infections by this method and only send to the laboratory those specimens with positive findings. Using this method the routine laboratory workload involved in testing urine specimens would be reduced by 40%, instant results would be available in the general practitioner's surgery and the patient would receive immediate and appropriate treatment.
We compared the sensitivity, specificity, and predictive values of the 1-min leukocyte esterase test and the test for urinary nitrite alone and in combination as screening tests for bacteriuria in over 5,000 clinical urine specimens. The leukocyte esterase-nitrite combination had a sensitivity of 79.2%, a specificity of 81%, and a negative predictive value of a negative test of 94.5% for specimens with greater than or equal to 10(5) CFU/ml. Although the sensitivity of this test was too low to allow its use as the only screening test for bacteriuria, it may serve as a useful adjunct to culturing and other urine-processing systems in the microbiology laboratory.
Evaluations of screening tests for bacteriuria have traditionally compared the test results with those of quantitative urine cultures. However, many patients with symptomatic urinary tract infections can have less than 10(5) CFU/ml in their urine. Therefore, the results of urine culture and three screening tests (Bac-T-Screen, Chemstrip LN [which tests for leukocyte esterase and nitrate reductase], and Gram stain) were correlated with the clinical classification of urinary tract infection. The Bac-T-Screen test detected 98, 93, and 100% of the infections classified as probable, possible, and asymptomatic, respectively. In contrast, the Gram stain, leukocyte esterase, and nitrate reductase tests were all insensitive screening tests for infection. Additionally, only 45% of the patients with probable infections had greater than or equal to 10(5) CFU/ml. Thus, the majority of infected patients would not have been detected if quantitative urine cultures were used alone.
Few studies have evaluated dipstick urinalysis for elderly and practically none present confidence intervals. Furthermore, most previous studies combine all bacteria species in a "positive culture". Thus, their evaluation may be inappropriate due to Yule-Simpson's paradox. The aim of this study was to evaluate diagnostic accuracy of dipstick urinalysis for the elderly in nursing homes.
In this cross-sectional study voided urine specimens were collected from 651 elderly individuals in nursing homes. Dipstick urinalysis for nitrite, leukocyte esterase and urine culture were performed. Sensitivity, specificity, positive and negative predictive values with 95% confidence intervals were calculated. Visual readings were compared to readings with a urine chemistry analyzer.
207/651 (32%) of urine cultures showed growth of a potentially pathogenic bacterium. Combining the two dipsticks improved test characteristics slightly compared to using only one of the dipsticks. When both dipsticks are negative, presence of potentially pathogenic bacteria can be ruled out with a negative predictive value of 88 (84–92)%. Visual and analyzer readings had acceptable agreement.
When investigating for bacteriuria in elderly people at nursing homes we suggest nitrite and leukocyte esterase dipstick be combined. There are no clinically relevant differences between visual and analyzer dipstick readings. When dipstick urinalysis for nitrite and leukocyte esterase are both negative it is unlikely that the urine culture will show growth of potentially pathogenic bacteria and in a patient with an uncomplicated illness further testing is unnecessary.
The present study evaluated the usefulness of the 1-min leukocyte esterase-nitrite tests in a tertiary-care hospital as a screening procedure to detect significant bacteriuria and correlated the findings with culture results. A total of 531 urine samples were reviewed, of which 484 were evaluated. Of the evaluated samples, 113 positive cultures (23.4%) were found, of which 93 (82.3%) were detected by leukocyte esterase-nitrite tests. In addition, 365 of 371 (98.4%) urine samples with negative bacterial cultures were negative in leukocyte esterase and nitrite tests.
The Chemstrip LN (Boehringer Mannheim Biochemicals, Indianapolis, Ind.), designed to detect pyuria and bacteriuria, was compared with culture of 1,020 unselected, consecutive midstream urine specimens and evaluated on its ability to predict colony counts at three levels. At the level of greater than or equal to 10(5) CFU/ml, the combined test (detection of leukocyte esterase and nitrite) had sensitivity of 82.3%, specificity of 67.9%, positive predictive value of 41.3%, and negative predictive value of 93.3% at prevalence rate of 21.6%. The test would have rejected 9.4% of the specimens with significant bacteriuria if the Chemstrip alone had been used.
In an ongoing national study of women to identify risk factors for interstitial cystitis/painful bladder syndrome (IC/PBS), dysuria was identified at onset of IC/PBS in a small majority and evidence for urinary tract infection (UTI) was evaluated.
In women with IC/PBS of ≤12 months duration, symptoms and pertinent laboratory tests at onset were assessed by telephone interview and medical record review.
Of 138 cases, 75 (54%) reported that they started to experience burning or pain on urination at onset of IC/PBS. Of those with urines cultured, 12/35 (34%) with dysuria vs. 1/21 (5%) without dysuria yielded a uropathogen (p=.01). Similarly, microscopic WBC and dipstick nitrites and leukocyte esterase were each significantly more common in urines of those with dysuria than those without. Additionally, 7/75 of those with dysuria vs. 1/62 without dysuria reported chills or fever at onset of IC/PBS. Using various definitions, the prevalence of UTI at onset of IC/PBS, at a minimum, was 16 – 33 % of those with dysuria vs. < 2% of those without dysuria (p ≤ .003).
A slight majority of women with IC/PBS reported dysuria at onset of their IC/PBS symptoms. Available laboratory data suggest dysuria may be a sensitive indicator of UTI at onset of IC/PBS; its specificity is as yet undetermined.
interstitial cystitis; painful bladder syndrome; dysuria; burning on urination; bacteriuria; urinary tract infection
A total of 4470 pregnant women were screened for bacteriuria by the dipslide method and significant growth found in 226 (5.1%). In 198 cases the urine was re-examined, in 119 by using suprapubic aspiration or catheterisation (62 (52%) samples contained bacteria) and in 79 by using midstream urine samples (26 (33%) samples contained greater than 10(8) colony forming units/1), showing the maximum prevalence of confirmed bacteriuria to be 2.6%. Overt urinary tract infection developed later in four of 80 patients with proved bacteriuria who had been given antibiotics, in one of eight untreated patients with bacteriuria, in one of 110 patients with unconfirmed bacteriuria, and in one of 226 non-bacteriuric controls. A history of urinary tract infection was given by 18% of controls and 42% of women with confirmed bacteriuria. Screening for bacteriuria and treatment with antibiotics to prevent later overt infection is expensive. Whether it is worth while and cost effective depends largely on the prevalence of bacteriuria in the local population and the proportion who develop overt infection. The screening and treatment programme reported here appeared to prevent only six cases of overt infection.
A new sensitive nitrite test, the SRN test, was evaluated for its suitability as a reliable screening technique for the detection of bacteriuria. The SRN test was compared to a currently available nitrite test, the Microstix nitrite test, and the results obtained with both nitrite tests were assessed in comparison with the results of the quantitative culture method. Of 158 cases of significant bacteriuria found among 1060 randomly collected specimens, the SRN test detected 90% and the Microstix nitrite test, 30%. The higher reliability of the SRN test reflects its high capability of nitrite detection (greater than or equal to 0.1 ppm), and its ability to overcome interference by various factors, such as dark colour of the urine, presence of phenazopyridine, urobilinogen, blood, high concentration of ascorbate, and high urinary pH, all of which do interfere with the Microstix nitrite test. The high sensitivity of the SRN test allows detection of bacteriuria in urine specimens collected at random throughout the day; the test is therefore not restricted to the use of first-morning samples as are other nitrite tests. Since the SRN test was found to give a quantitative indication of the size of the bacterial population, the possibility of its use as an exact quantitative test under controlled conditions its discussed.
Two hundred and forty-three urine specimens from 76 elderly institutionalized residents were obtained for urine culture, quantitative leukocyte count and urinalysis. Significant bacteriuria was present in 153 specimens (63%), including 33 (22%) with more than one organism. Pyuria (greater than or equal to 10 leukocytes/mm3) was present in 214 specimens (88%), including 116 (97%) with single organism bacteriuria, 27 (82%) with multiple organism bacteriuria, and 71 (80%) without significant bacteriuria. The leukocyte esterase test had a positive predictive value of 99% for pyuria but a negative predictive value of only 30%. The quantitative level of pyuria was associated with the level of proteinuria and inversely with pH. A relatively constant level of pyuria tended to persist over months to years in a given individual if bacteriuria persisted. Pyuria is significantly associated with bacteriuria in the institutionalized elderly, but is also common in the nonbacteriuric. The clinical significance of pyuria requires further assessment.
Elderly; Pyuria; Urinalysis; Urinary infection
The 1-min leukocyte esterase (LE)-nitrite test (Chemstrip 9; Biodynamics, Division of Boehringer Mannheim Biochemicals, Indianapolis, Ind.) and a bioluminescence assay (Monolight centrifugation method; Analytical Luminescence Laboratory, Inc., San Diego, Calif.) were tested for their efficacy as urine screens among 453 patients at a tertiary-care teaching hospital. Both methods had the capacity to exclude significant bacteriuria (greater than or equal to 10(5) CFU/ml) when compared with the results of conventional culture methods, with predictive values of 99 and 93%, respectively, for a negative test. Bioluminescence was the more accurate nonculture method used. Sensitivity and specificity values were 97 and 71%, respectively, for bioluminescence, 82 and 60%, respectively, for LE with nitrite, and 72 and 64%, respectively, for LE without nitrite. At reduced levels of bacteriuria less than 10(5) CFU/ml), the sensitivities of LE-nitrite and bioluminescence were decreased but comparable. The addition of protein and blood test results in the Chemstrip 9, along with LE-nitrite as bacteriuria indicators, were unsatisfactory because of the large numbers of false-positive results attributed to protein and blood determinations. LE activity as detected by the LE test was a poor predictor of significant bacteriuria in both male and female patients. The sensitivity (71%) and specificity (57%) of the LE test in male patients were significantly lower than those previously reported and varied with the patient population studied.
OBJECTIVE: To evaluate the performance of reagent test strips in screening pregnant women for asymptomatic bacteriuria at their first visit to an antenatal clinic. DESIGN: Prospective case series. SETTING: Antenatal clinic of a large inner city maternity hospital. SUBJECTS: All women attending for their first antenatal clinic. Patients taking antibiotics for any reason and those with urinary tract symptoms were excluded. INTERVENTION: A midstream urine specimen was divided; half was sent for microscopy and formal bacteriological culture and the other half was tested with a commercial reagent strip test for the presence of blood, protein, nitrite, and leucocyte esterase. MAIN OUTCOME MEASURES: Sensitivity, specificity, and positive and negative predictive values of the reagent strips in diagnosing asymptomatic bacteriuria (defined as 10(5) colony forming units/ml urine). RESULTS: Sensitivity was low, with a maximum of 33% when all four tests were used in combination. Specificity was high, with typical values of 99% or more. Positive predictive value reached a maximum of 69% and negative predictive value was typically 95% or more. CONCLUSION: Urine reagent strips are not sufficiently sensitive to be of use in the screening for asymptomatic bacteriuria and therefore many patients would be missed. In view of the potentially serious sequelae of this condition in pregnant women we recommend that formal bacteriological investigation remain the investigation of choice in this group of patients.
In this study, urinary culture, urinary Gram stain, and four tests within the urinalysis, leukocyte esterase, nitrite, microscopyfor bacteria, and microscopyforpyuria, were examined in 100 children with symptoms suggesting urinary tract infection. Our purpose was to determine the validity of the urinary Gram stain compared with a combination of pyuria plus Gram stain and overall urinalysis (positiveness of nitrite, leukocyte esterase, microscopy for bacteria, or microscopy for white blood cell). Of 100 children, aged two days to 15 years, 70 (70 percent) had a positive urinary culture: 40 girls (57 percent) and 30 boys (43 percent). Escherichia coli was the most common isolated agent. The sensitivity and specificity of the urinary Gram stain were 80 percent and 83 percent, and that of the combination of pyuria plus Gram stain 42 percent and 90 percent, and that of the overall urinalysis 74 percent and 3.5 percent respectively. Our findings revealed that neither method of urine screen should substitute for a urine culture in the symptomatic patients in childhood.
Significant bacteriuria (SBU) and urinary tract infections (UTIs) are common in patients with spina bifida and neuropathic detrusor sphincter dysfunction. Laboratory agar plated culture is the gold standard to establish SBU. It has the disadvantage of diagnostic and subsequent therapeutic delay. Leukocyte esterase tests (LETs) and dip slides proved to be useful in the general populations to exclude SBU and UTI. The aim of this study was to evaluate the reliability of LET and dip slide in children with spina bifida without symptoms of UTI. The reliability in children with asymptomatic SBU was not studied before.
In one hundred and twelve children with spina bifida on clean intermittent catheterization LETs and dip slides were compared with laboratory cultures. Both tests and agar plated cultures were performed on catheterized urine samples. The hypothesis was that the home tests are as accurate as laboratory cultures.
A SBU was found in 45 (40%) of the 112 laboratory cultures. A negative LET excluded SBU (negative predictive value 96%), while a positive LET had a positive predictive value of 72%. The false positive rate was 28%. Dip slide determination of bacterial growth had no added value, other than serving as transport medium.
In spina bifida children, leukocyte esterase testing can be used to exclude significant bacteriuria at home, while dip slide tests have no added value to diagnose or exclude significant bacteriuria.
Bacteriuria; Clean intermittent catheterization; Dip slide; Home testing; Leukocyte esterase test; Spina bifda
It is known that there is significant morbidity associated with urinary tract infection and with renal dysfunction in sickle cell disease (SCD). However, it is not known if there are potential adverse outcomes associated with asymptomatic bacteriuria (ASB) infections in sickle cell disease if left untreated. This study was undertaken to determine the prevalence of ASB, in a cohort of patients with SCD.
This is a cross-sectional study of patients in the Jamaican Sickle Cell Cohort. Aseptically collected mid-stream urine (MSU) samples were obtained from 266 patients for urinalysis, culture and sensitivity analysis. Proteinuria was measured by urine dipsticks. Individuals with abnormal urine culture results had repeat urine culture. Serum creatinine was measured and steady state haematology and uric acid concentrations were obtained from clinical records. This was completed at a primary care health clinic dedicated to sickle cell diseases in Kingston, Jamaica. There were 133 males and 133 females in the sample studied. The mean age (mean ± sd) of participants was 26.6 ± 2.5 years. The main outcome measures were the culture of ≥ 105 colony forming units of a urinary tract pathogen per milliliter of urine from a MSU specimen on a single occasion (probable ASB) or on consecutive occasions (confirmed ASB).
Of the 266 urines collected, 234 were sterile and 29 had significant bacteriuria yielding a prevalence of probable ASB of 10.9% (29/266). Fourteen patients had confirmed ASB (prevalence 5.3%) of which 13 had pyuria. Controlling for genotype, females were 14.7 times more likely to have confirmed ASB compared to males (95%CI 1.8 to 121.0). The number of recorded visits for symptomatic UTI was increased by a factor of 2.5 (95% CI 1.4 to 4.5, p < 0.005) but serum creatinine, uric acid and haematology values were not different in patients with confirmed ASB compared with those with sterile urine. There was no association with history of gram negative sepsis.
ASB is a significant problem in individuals with SCD and may be the source of pathogens in UTI. However, further research is needed to determine the clinical significance of ASB in SCD.
The value of the one minute leucocyte esterase-nitrite chemical strips as a screening procedure for detecting appreciable levels of pyuria and bacteriuria was assessed by comparison with microscopy and culture results. The likelihood that a negative leucocyte esterase result indicated less than 10 white cells/cu mm by microscopy (the negative predictive value), was 90.1% and that a negative nitrite result indicated less than 10(5) organisms/ml was 91.3%. There were many false positive results with both tests, however, and the overall predictive value of a positive leucocyte esterase or nitrite test, or both, was low. The leucocyte esterase-nitrite strip was neither sufficiently sensitive nor specific enough to be used as a cost effective method for screening urines in the laboratory.
A disposable kit was tested as a means of detecting significant bacteriuria by quantitative culture of urine. The total error in 3,563 specimens tested by five investigators was less than 1%. The method was very effective in differentiating significant bacteriuria, i.e., more than 100,000 bacteria per ml of urine from uninfected urine. In specimens from patients with urinary tract abnormalities who had mixed bacterial flora, the absolute numbers obtained with the dip-inoculum method had a 10% variation when compared to results obtained by calibrated loop or dilution pour plate methods. Therefore, the main utility of the kit is for screening and following patients after therapy. A significant delay in time between inoculation of the medium in the kit with the freshly voided urine and incubation of the kit to promote growth did not affect the reliability of the kit as a method of doing quantitative urine cultures to detect bacteriuria.
AIM: To compare the performance of leucocyte esterase and nitrite dipstick tests with microscopic examination and culture of first morning urines (n = 420) of hospital inpatients. RESULTS: The sensitivity, specificity, and negative predictive value of the leucocyte esterase test for the cutoff of > 10 WBC/microliter were 57%, 94%, and 68%, respectively. For > 5 WBC per high power field (HPF) these variables were 84%, 90%, and 93%. For > 10(5) colony counts/ml, the sensitivity of the nitrite test was 27%, specificity 94%, and negative predictive value 87%. When either leucocyte esterase or nitrite positivity was accepted as a marker of urinary tract infection, the sensitivity was 78%, specificity 75%, and negative predictive value 94%, and there were 22% false negative results. Semiquantitative microscopic estimation of bacteria per HPF yielded 40% false positives. CONCLUSIONS: Leucocyte esterase and nitrite dipstick tests are not suitable for screening for urinary tract infections.
BACKGROUND AND OBJECTIVES--The leukocyte esterase (LE) strip is a useful tool for the screening of men with urethritis. In developing countries, where laboratory facilities are limited, and sexually transmitted diseases endemic, simple and inexpensive diagnostic tests which perform well, would be of great value. METHODS--Men presenting with urethritis to a referral clinic for sexually transmitted diseases in Nairobi, Kenya participated in this cohort analytical study. First-void urine was collected for LE dipstick testing as part of the diagnostic work-up. The results of the dipstick measurement were compared with the laboratory detection of Chlamydia trachomatis and Neisseria gonorrhoeae. RESULTS--Of 200 men with symptoms of urethritis, 33 (17%) had a pathogen detected from the urethra or the urine. Chlamydia was detected in urine by PCR in 22 (11%), and gonorrhoea was cultured from the urethra in 11 (6%). Esterase activity (trace or greater) had a sensitivity of 76%, a specificity of 80%, a positive predictive value of 42% and a negative predictive value of 94% for the presence of chlamydia or gonorrhoea. CONCLUSIONS--The use of the LE dipstick for the screening of men with symptomatic urethritis can improve diagnostic accuracy and reduce the amount of empiric antimicrobial therapy. The low detection rate of chlamydia in these men with a clinical diagnosis of nongonococcal urethritis needs further study.