Validating the prediction of lower urinary tract infection in primary care: sensitivity and specificity of urinary dipsticks and clinical scores in women

Background

Dipsticks are one of the most commonly used near-patient tests in primary care, but few clinical or dipstick algorithms have been rigorously developed.

Aim

To confirm whether previously documented clinical and dipstick variables and algorithms predict laboratory diagnosis of urinary tract infection (UTI).

Design of study

Validation study.

Setting

Primary care.

Method

A total of 434 adult females with suspected lower UTI had bacteriuria assessed using the European Urinalysis Guidelines.

Results

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.

Conclusion

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.     

Use of rapid dipstick tests to exclude urinary tract infection in children.

Children presenting with symptoms attributable to urinary tract infection (UTI) are not uncommonly referred to paediatric departments for assessment. The aim of this study was to evaluate the use of rapid dipstick tests in the diagnosis of urinary tract infection in children. Urine was collected from 375 children admitted to a general paediatric ward, in whom UTI was a possibility on clinical grounds. Of these, 124 were less than one year old. Urine was tested with a dipstick for the presence of nitrite and leucocyte esterase. Bacterial culture and examination for white cells, red cells and other formed elements were performed. The results of the dipstick tests, microscopy and culture were correlated with the clinical details. Combination of a negative dipstick test for nitrite and leucocyte esterase showed a negative predictive value for UTI of 96.9% and a specificity of 98.7%. In children less than a year old these values were 96.7% and 99.2% respectively. The leucocyte esterase strip test showed a negative predictive value for pyuria of 94.3% with a specificity of 86.9%. In children less than a year old these values were 93.1% and 84.4% respectively. The use of dipsticks for the detection of urinary nitrate and leucocyte esterase in daily clinical practice is recommended. In children, the absence of both nitrite and leucocyte esterase in urine indicates that UTI is unlikely; however, positive dipstick tests for nitrite and/or leucocyte esterase are not specific indicators of UTI, and should not be used in place of laboratory examination. The dipstick method is most likely to be useful as a screening test to exclude UTI in children, but may be less suitable for infants. It should not be used to diagnose urinary tract infection.     

Evaluation of a screening test for detecting urinary tract infection in newborns and infants.

The results of a study of a screening test for urinary tract infection (UTI) in infants under 18 months is reported. Two hundred and forty three urine specimens were tested in the laboratory using AMES Multistix 8SG reagent strips read by photometer. The strips included three potential markers for urinary tract infection: leucocyte esterase, nitrite, and protein. The predictive value of a positive result (PPV) was low. The predictive value of negative test (NPV) when combining the screen of leucocyte esterase, nitrite, and protein was 99.4% with no difference between boys and girls. The test for leucocyte esterase had a 97.6% negative predictive value. An examination of the results by age confirms the good NPV in all age groups. Paediatricians should find Multistix 8SG strips a useful aid in the diagnosis of urinary tract infection in infants, and that costly culture of samples with negative strip tests can be avoided.     

Screening for urinary tract infections in a gynaecological setting: validity and cost-effectiveness of reagent strips

This study aims to test the validity and cost-effectiveness of reagent-strip analysis compared with microbiological laboratory testing for mass screening of urine for urinary tract infections in a gynaecological setting. Over a six-month period, urine samples from a convenient group of 228 women presenting in a gynaecological ward of an NHS Trust hospital were tested using Ames 8SG reagent strips to detect leucocyte esterase and nitrite. Total bacterial counts were also carried out; urine culture was recorded as positive if there was > 10(5) organisms/mL. Validity of the dipstick tests was measured, using four criteria (sensitivity, specificity, positive predictive value [PPV] and negative predictive value [NPV]), against the results of laboratory analysis. The combined use of the leucocyte esterase and nitrite tests produced results as follows: sensitivity, 96.4%; specificity, 88.5%; PPV, 54%; and NPV, 99.4%. Cost-effectiveness for visible costs was calculated as 48.6% for the 12.3% rate of infection in this study. The use of reagent strips in a mass-screening programme in a gynaecological setting proved both valid and cost-effective.     

Disappointing dipstick screening for urinary tract infection in hospital inpatients.

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.     

The diagnostic accuracy of rapid dipstick tests to predict urinary tract infection

This study summarizes the diagnostic accuracy data for dipstick nitrite and/or leukocyte esterase tests (the index tests) as predictors of bacterial urinary tract infection as defined by quantitative culture (the reference test). On-line search of the literature using the MEDLARS database identified 1,017 citations, 51 of which were relevant and contained sufficient data for further analysis. From each citation, 2 x 2 tables of true-positive, true-negative, false-positive, and false-negative results were extracted. Four categories of index test were assessed: nitrite only, leukocyte esterase only, disjunctive pairing (dipstick positive if nitrite, leukocyte esterase, or both were positive), and conjunctive pairing (dipstick positive only if both nitrite and leukocyte esterase were positive). The true- and false-positive rates were calculated from each 2 x 2 table. Plots of true-positive rates versus false-positive rates demonstrated widely scattered points, indicating heterogeneity. A receiver-operating characteristic curve was fitted to the data using logistic transforms and weighted linear regression. This analysis revealed that the disjunctive pair is the most accurate index test. However, in many clinical settings, the posterior probability of urinary tract infection given a negative dipstick is too high to exclude it. Within most clinically relevant ranges of true- and false-positive rates, a negative urine dipstick test cannot exclude the diagnosis of urinary tract infection in patients with high prior probabilities of contracting this infection. For lower prior probabilities, the clinical efficacy of these rapid tests would best be determined by decision analysis, for which these receiver-operating characteristic functions would serve as valuable analytical tools.     

Management of acute uncomplicated urinary tract infections in general practice in the south of The Netherlands.

There is debate about the ideal diagnostic procedure for urinary tract infections (UTIs) in general practice. The aim of this study was to evaluate nitrite and leucocyte esterase strip test procedures in general practice patients, and to relate the results to the decision of the general practitioner to prescribe antibiotic therapy. A total of 292 female patients from eight general practices in the Maastricht area, who were aged 12 years or over with complaints suggesting UTI, were included in the study. All eight practices tested fresh urine samples using the nitrite strip test, and seven also used the leucocyte esterase strip test. The positive predictive value of the nitrite test was greater than the leucocyte test. Antibiotic therapy was nearly always prescribed when either or both of these tests were positive. Bacterial culture was positive in 159 (59%) cases, although treatment was started in 70 (27%) cases where there was an absence of significant bacteruria. It was found that the choice of agent used to treat the patient was related to the antibiotic susceptibility of the uropathogens that were isolated.     

Detection of neutrophilocytes and NO2-producing bacteria in urine by dipstick BM-test-9

A prospective study compared the detection of leucocytes and bacteria in urine with the dipstick test (presence of esterases in granulocytes and nitrite) to chamber counting of urine, microscopic examination of the urinary sediment, and urine culture. Examined were 174 urine specimens. The dipstick esterase test and the sediment count were almost equally sensitive in detecting leucocyturia. Using chamber count and a cut-off point of 10 or more leucocytes per cubic millimeter as denoting significant leucocyturia, the esterase test gave a predictive value for negative test (PV neg) of 75% and a predictive value for positive test (PV pos) of 96%. PV neg of the dipstick nitrite test was 78% and PV pos 100% in detecting bacteriuria (10(5) bacteria per milliliter). Combining the esterase test with the nitrite test did not increase PV neg. Our result was that the dipstick test seems to be a simple screening procedure for leucocyturia and bacteriuria. The test is suggested to replace the time-consuming microscopic examinations of urine for leucocytes. When the nitrite test is positive, routine urine culture may be omitted.     

Leucocyte esterase-nitrite screening method for pyuria and bacteriuria.

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.     

The use of urinary dipstick tests to exclude urinary tract infection: a systematic review of the literature

Several systematic reviews have examined the use of dipstick tests to diagnose or rule in urinary tract infection (UTI). We examined the evidence relating to the use of urine leukocyte esterase and nitrite tests in adults to exclude or rule out UTI. A search of the literature from 1966 to 2003 revealed 30 studies as containing relevant and suitable information and 23 of these, which used a cut-off of 108 colony-forming units per liter, were combined in a meta-analysis. The leukocyte esterase or nitrite test combination, with one or the other test positive, was used in 14 studies, showed the highest sensitivity and the lowest negative likelihood ratio. While there was significant heterogeneity between the studies, 7 of 14 demonstrated significant decreases in pretest to posttest probability with a pooled posttest probability of 5% for the negative result. In certain circumstances, there is evidence for the use of urinalysis as a rule-out test for UTI.     

Evaluation of various screening tests to detect asymptomatic bacteriuria in pregnant women

To evaluate the diagnostic efficacy of various screening tests in detecting asymptomatic bacteriuria among pregnant women. Clean catch midstream urine specimens were collected from 630 consecutive pregnant women and processed. Forty-four (7.4%) of the urine samples were culture positive, with Escherichia coli as the predominant organism isolated (57.4%). The results of the four screening tests, viz., Gram's staining of uncentrifuged urine, pus cell count, nitrite test and leukocyte esterase (LE) test, were compared against urine culture. Gram's stain of the uncentrifuged urine was found to be the single most useful test with a sensitivity and negative predictive value (NPV) of 85.1% and 98.8%, respectively. Pus cell count was the least sensitive. Neither the nitrite test nor the LE test alone was sensitive enough with 74.4% and 61.7%, respectively. However, when either or both tests positive were considered, it increased the sensitivity and NPV comparable with Gram's staining results, with 82.9% and 98.8%, respectively. With the potential to be used as an office diagnostic procedure, the combined nitrite and LE dipstick test may provide an acceptable alternative.     

Comparative evaluation of three chromogenic agars for detection and rapid identification of aerobic Gram-negative bacteria in the normal intestinal microflora

Objective  To compare three different chromogenic agars and MacConkey agar for the detection of aerobic Gram-negative bacteria in the normal intestinal microflora and to assess the accuracy of the chromogenic agars for the direct identification of Escherichia coli .
Methods  A total of 164 Gram-negative clinical isolates ( E. coli , Proteus , Klebsiella , Enterobacter , Morganella and Pseudomonas species) and 30 stool specimens were inoculated in parallel on four media: Chromagar E. coli /Coliform, Chromogenic urinary tract infection UTI medium, CHROMagar Orientation and MacConkey agar. All colonies that differed by color and/or morphology were selected for further identification by VITEK 1 and/or API 20E from each medium.
Results  On E. coli /Coliform agar five out of 32 (16%) E. coli strains failed to produce the color as described by the manufacturer. No remarkable discrepancies were found for the other clinical isolates. There was no significant difference in detection rate (DR) of aerobic Gram-negative bacteria in stool specimens between the different chromogenic agars and MacConkey agar. The overall DR was about 84%, and varied from 100% for monomicrobial specimens to 33% for polymicrobial specimens. The positive predictive values (PPV) for the direct identification of E. coli on Chromagar E. coli /Coliform, Chromogenic UTI medium and CHROMagar Orientation were 1.00, 0.93 and 0.93, respectively. The negative predictive values (NPV) were 0.53, 0.68 and 0.69, respectively.
Conclusion  Chromogenic UTI medium and CHROMagar Orientation are the preferred media because of the higher NPV. The high PPV of these agars allows accurate and rapid identification of E. coli .     

Comparison between clinical examination, transvaginal sonography and magnetic resonance imaging for the diagnosis of deep endometriosis

BACKGROUND: Deeply infiltrating endometriosis affecting the retrocervical region and the rectosigmoid generally requires surgical treatment. Clinical examination, transvaginal ultrasonography (TVUS) and pelvic magnetic resonance imaging (MRI) are useful in the preoperative diagnosis of the involvement of these sites. The objective of this study was to evaluate the capacity of digital vaginal examination, TVUS and MRI to diagnose rectosigmoid and retrocervical involvement. METHODS: A total of 104 patients with clinically suspected endometriosis were submitted to clinical examination, pelvic MRI and TVUS until 3 months prior to videolaparoscopy and the findings of these methods were matched with histopathological confirmation of endometriosis. RESULTS: Endometriosis was histologically confirmed in 98 of 104 (94.2%) patients. With respect to the rectosigmoid and retrocervical sites, respectively, digital vaginal examination had a sensitivity of 72 and 68%, specificity of 54 and 46%, positive predictive value (PPV) of 63 and 45%, negative predictive value (NPV) of 64 and 69% and accuracy of 63 and 55%. For TVUS, sensitivity was 98 and 95%, specificity 100 and 98%, PPV 100 and 98%, NPV 98 and 97% and accuracy 99 and 97%. MRI had a sensitivity of 83 and 76%, specificity of 98 and 68%, PPV of 98 and 61%, NPV of 85 and 81% and accuracy of 90 and 71%. CONCULSIONS: TVUS had better sensitivity, specificity, PPV, NPV and accuracy in cases of deep retrocervical and rectosigmoid endometriosis when compared with MRI and digital vaginal examination, confirming that it is an important preoperative examination for the definition of surgical strategies.     

The clinical significance of dipstick-negative, culture-positive urines in a veterans population

The consequences of omitting cultures in dipstick-negative urines submitted to the authors' microbiology laboratory were evaluated retrospectively in 1,079 clean-catch midstream samples. Using positive dipstick readings for leukocyte esterase, nitrite, and/or protein as evidence of a positive screen, the sensitivity, specificity, positive predictive value, and negative predictive value for specimens containing more than or 10(3) CFUs/mL (10(6)/L) were 80%, 71%, 48%, and 91%, respectively. Clinical data were reviewed in 38 patients with one or more dipstick-negative, culture-positive urines. Most of these patients lacked clinical or other laboratory evidence suggesting urinary tract infection. Problems with specimen collection were suspected in 19 neurologically compromised patients. Only two patients with dipstick-negative urines received treatment based on the culture reports. Symptoms persisted in both. The authors conclude that in their predominantly male veteran population, clinically significant bacteriuria is an unlikely finding in a dipstick-negative urine.     

Multicenter, prospective clinical evaluation of respiratory samples from subjects at risk for Pneumocystis jirovecii infection by use of a commercial real-time PCR assay

Pneumocystis jirovecii pneumonia (PCP) is a common opportunistic infection. Microscopic diagnosis, including diagnosis using the Merifluor-Pneumocystis direct fluorescent antigen (MP-DFA) test, has limitations. Real-time PCR may assist in diagnosis, but no commercially validated real-time PCR assay has been available to date. MycAssay Pneumocystis is a commercial assay that targets the P. jirovecii mitochondrial large subunit (analytical detection limit, ≤ 3.5 copies/μl of sample). A multicenter trial recruited 110 subjects: 54 with transplants (40 with lung transplants), 32 with nonmalignant conditions, 13 with leukemia, and 11 with solid tumors; 9 were HIV positive. A total of 110 respiratory samples (92% of which were bronchoalveolar lavage [BAL] specimens) were analyzed by PCR. Performance was characterized relative to investigator-determined clinical diagnosis of PCP (including local diagnostic tests), and PCR results were compared with MP-DFA test results for 83 subjects. Thirteen of 14 subjects with PCP and 9/96 without PCP (including 5 undergoing BAL surveillance after lung transplantation) had positive PCR results; sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) were 93%, 91%, 59%, and 99%, respectively. Fourteen of 83 subjects for whom PCR and MP-DFA test results were available had PCP; PCR sensitivity, specificity, PPV, and NPV were 93%, 90%, 65%, and 98%, respectively, and MP-DFA test sensitivity, specificity, PPV, and NPV were 93%, 100%, 100%, and 98%. Of the 9 PCR-positive subjects without PCP, 1 later developed PCP. The PCR diagnostic assay compares well with clinical diagnosis using nonmolecular methods. Additional positive results compared with the MP-DFA test may reflect low-level infection or colonization.     

A urine analysis method suitable for children's nappies.

BACKGROUND: Urinary tract infection in infancy continues to be underdiagnosed, despite its association with renal scarring and thus hypertension, renal failure, and other sequelae. Low ascertainment of urinary tract infections reflects the many difficulties in establishing a diagnosis, some of which could be eliminated by a simple, reliable method for preliminary investigation of children's urine. AIM: To assess the accuracy of a new, simple method for testing urine for nitrite and leucocyte esterase, which could be applied to children in primary care. METHODS: An in vitro study was carried out to compare the results of conventional urine analysis with urine analysis on urine soaked on to panty-liners, and with the laboratory investigation. Two urine analysis stick types were used (Boehringer Mannheim Nephur sticks and Bayer Multistix 8SG) and two brands of panty-liners. Analysis examined evidence of agreement and bias for different methods in addition to sensitivity, specificity, and negative predictive values for urine analysis. RESULTS: Pressing urine analysis test sticks on to panty-liners soaked with urine achieved consistent results compared with the results of conventional dipstick urine analysis. At a prevalence of 21.8%, sensitivity and negative predictive values of urine analysis for laboratory confirmed urinary tract infection were 94% and 98%, respectively, for Boehringer sticks, and 76% and 93%, respectively, for Bayer sticks. At prevalences of 5% and 1% (prevalences that could be expected in primary care) Bayer sticks had negative predictive values of 98.7% and 99.7%, respectively, and Boehringer sticks had values of 99.6% and 99.9%, respectively. CONCLUSIONS: Testing urine on panty-liners is accurate compared with conventional urine analysis. It may be possible to apply this method to testing unwell children presenting in primary care to identify those who require microbiological urine culture to confirm or eliminate a diagnosis of urinary tract infection.     

Field evaluation of a second-generation cytometer UF-100 in diagnosis of acute urinary tract infections in adult patients

Aims   The authors evaluated the analytical performance of the Sysmex UF-100 cytometer vs. the diagnosis of urinary tract infections (UTI).
Methods   We considered 2010 subjects, aged between 18 and 78, 870 males and 1140 females. The majority (90.2%) of the samples were voided urine specimens collected by using the midstream technique. Each sample was subjected to microbiological evaluation (culture + residual antibacterial activity), dipstick tests, UF-100 examination and microscopic observation. In order to obtain a final diagnosis of UTI these laboratory results were taken into consideration together with clinical data and patients' characteristics. The analytical performance of the laboratory tests was obtained by adopting this diagnosis as standard practice.
Results   Out of the total 2010 subjects considered a clinical diagnosis of UTI was obtained in 529 cases (26.32%). The UF-100-based screening had sensitivity, 0.94; specificity, 0.93; positive predictive value, 0.83; negative predictive value, 0.98; and correctly classified incidence, 0.93.
Conclusions   In our experience the results of the UF-100-based screening show a very good correlation with the diagnosis of acute UTI in adults patients.     

Comparison of five techniques to detect anti-Saccharomyces cerevisiae antibodies (ASCA) in serum for diagnosing Crohn's disease

OBJECTIVE: the anti-Saccharomyces cerevisiae antibodies (ASCA) are diagnostic markers found in Crohn's disease patients. The aim of this study was to compare three Elisa (enzyme linked immunosorbent assay) kits with the indirect immunofluorescence (IFI) technique and an immunodot for ASCA detection. MATERIALS AND METHODS: we compared the results obtained using IFI (IgA and IgG) and Elisa (IgA and IgG) in 139 patients (37 Crohn's disease). An immunodot (IgA+IgG) was tested in a sub-group of 24 patients (18 Crohn's disease). RESULTS AND DISCUSSION: for the different techniques by Elisa (IgA or IgG), the sensitivity ranged from 65% to 76%, the specificity from 88% to 98%, the positive predictive value (PPV) from 84% to 94% and the negative predictive value (NPV) from 88% to 93%. For IFI, the sensitivity was 81%, the specificity 100%, the PPV 100% and the NPV 93%. The immunodot showed a specificity and PPV of 100% and NPV of 33%. CONCLUSION: the detection of the ASCA is useful in the diagnosis of Crohn's disease. IFI appears as the method of choice for its excellent sensitivity and specificity, and affordable costs.     

A correlation study on diagnostic endoscopic ultrasound-guided fine-needle aspiration of lymph nodes with histological and clinical diagnoses, the UCLA Medical Center experience

Endoscopic ultrasound guided (EUS) FNA procedure has two aspects, the endoscopic sampling and the FNA interpretation. The two aspects of the procedure are performed in two different disciplines; gastroenterology (EUS) and pathology (FNA). The aim of this study was to evaluate the concordance, sensitivity, specificity, positive predictive (PPV), and negative predictive values (NPV).Sixty-one EUS-FNA procedures of the lymph nodes were analyzed by correlating the FNA results with histological or clinical diagnoses. The lymph nodes were divided in five groups; mediastinal, gastrohepatic, peripancreatic, portal, and perirectal.The study showed a concordance of 92% in mediastinal, 80% in gastrohepatic, 81% in peripancreatic, 95% in portal, and 100% in perirectal lymph nodes with an overall sensitivity of 84%, specificity of 92%, PPV of 88%, and NPV of 89%. In conclusion, EUS-FNA offers an invaluable approach for diagnostic examination of the internal lymph nodes where percutaneous FNA is either difficult or impossible. impossible.