Performance of Urinalysis Parameters in Predicting Urinary Tract Infection: Does One Size Fit all?

In a multi-hospital cohort study of 3392 patients, positive urinalysis parameters had poor positive predictive value for diagnosing urinary tract infection (UTI). Combined urinalysis parameters (pyuria or nitrite) performed better than pyuria alone for ruling out UTI. However, performance of all urinalysis parameters was poor in older women.

A simplified fecal leukocyte esterase strip test results as a low cost, widely available, alternative bowel inflammation biomarker.

BACKGROUND: /Purpose: Leukocyte esterase strips have been widely used to detect the presence of leukocyte in human body fluids. We investigated the correlation between fecal leukocyte esterase (FLE) and fecal calprotectin (FC) levels and compared manual with machine automated interpretation of FLE level. METHODS: This prospective study enrolled inflammatory bowel disease and colitis patients in National Taiwan University Hospital from Dec 2021 to Feb 2022. FLE and FC measured using the same sample were compared with various FC cutoff values. The correlation between values indicated by the two tests was analyzed. Sensitivity, specificity, positive and negative predictive values, and area under the receiver operating characteristic curve (AUROC) were calculated using SAS. RESULTS: A total of 103 samples were analyzed. The correlation between FLE and FC level was moderate and positive (r = 0.3505, P = 0.0003). With an FLE reading more than 1+ indicating mucosa inflammation, when the FC cutoff was 50, 250, and 500 mg/kg, the sensitivities of FLE readings were 60.3 %, 74.3 %, and 84.6 %, respectively, and the specificities were 62.9 %, 58.8 %, and 58.4 %, respectively. With an FLE reading greater than 1+ indicating mucosa inflammation, FLE reflected FC with AUROC values at the optimal cutoff (500 mg/kg) of 0.72. No difference was noted between manual and machine readings for FLE. CONCLUSION: Positive FLE can predict FC levels of more than 500 mg/kg. The test is widely available, produces results on the same day, and is low cost; therefore, FLE should be further investigated for use in bowel inflammation monitoring.

Bedside Leukocyte Esterase Testing to aid in Diagnosing Bacterial Conjunctivitis in Children.

BACKGROUND: Conjunctivitis is a frequent symptom in pediatric emergency departments; however, the etiology of conjunctivitis is difficult to clinically differentiate. OBJECTIVE: Our study objective was to evaluate the test performance characteristics of leukocyte esterase (LE) test strips in diagnosing bacterial conjunctivitis. METHODS: Patients aged from 3 months through 21 years presenting to an emergency department with symptoms of conjunctivitis were prospectively enrolled from September 2018 to March 2020. A swab of the affected eye was applied to the LE test strip and another swab was sent for culture processing. The primary outcome was the association between LE test results and eye culture results. RESULTS: We enrolled 189 patients. Overall, 117 eye cultures (62%) were positive. The sensitivity and specificity of LE testing was 96% (95% CI 90-98%) and 14% (95% CI 7-25%), respectively. Positive predictive value was 64% (95% CI 57-71%) and negative predictive value was 67% (95% CI 39-87%). CONCLUSIONS: The LE test strip had limited ability to differentiate bacterial conjunctivitis from other etiologies.

Leukocyte esterase and alpha-defensin in periprosthetic joint infection: predictive quality and correlation in a prospective study.

PURPOSE: Periprosthetic joint infection (PJI) is a rare but serious complication of total joint arthroplasty (TJA). An accurate diagnosis of PJI preoperatively does not exist. Alpha-defensin (AD) is a proven and common indicator. The diagnostic marker of leukocyte esterase (LE) promises some advantages: feasibility, availability, and fast result reporting. The aim of this study was the evaluation of the predictive quality and correlation between both diagnostic tools in the diagnosis of PJI. METHODS: A prospective study was conducted between April 2018 and August 2022. All patients with suspicion of PJI on hip and knee joint were included and underwent a routine and standardized joint punction. For laboratory diagnostics of AD, the synovial liquid was analyzed by ELISA. The sample was additionally applied to a LE test strip (Combur 10 Test, Roche Diagnostics, Mannheim, Germany). RESULTS: A total of 249 patients were examined (mean age 67.12 ± 11.89; gender distribution man/woman 139 (55.8%)/110(44.2%), hip/knee 71(28.5%)/178 (71.5%). According to EBJIS criteria, PJI was diagnosed in 54 (21.7%) patients. AD showed excellent results with an AUC of 0.930 (sensitivity/specificity 0.870/0.990). LE yielded very good results with an AUC of 0.820 (sensitivity/specificity 0.722/0.918). Both parameters showed a strong positive correlation. CONCLUSION: LE is a rapidly available alternative in PJI diagnostics. The simultaneous determination of both markers may enhance diagnostic reliability. A routine usage may shorten the time from diagnosis to treatment of PJI.

Salivary leukocyte esterase activity by SillHa is a risk indicator of periodontal disease.

BACKGROUND: There is increasing evidence that diagnostic salivary tests measuring inflammatory biomarkers are being developed to assess inflammatory status for early detection, prevention, and progression of periodontal disease. Therefore, the aim of the present study was to investigate and identify the salivary biomarker that can predict the inflammatory status of periodontal disease. METHODS: A total of 36 patients (28 women and 8 men) with an average age of 57 years were investigated. Unstimulated saliva was collected from the recruited subjects and analyzed using SillHa, a saliva-testing device that measures bacteria count, saliva buffer capacity, acidity, leukocyte esterase, protein, and ammonia. Periodontal parameters were then obtained by clinical examination and initial periodontal therapy was performed. Data obtained with SillHa were compared with clinical periodontal parameters at baseline, re-examination (three months from baseline), and final examination (six months from re-examination). RESULTS: Leukocyte esterase activity in saliva measured by SillHa; BOP and PCR measured by clinical examination showed a significant difference between baseline and final examination and between re-examination and final examination. Patients in the lower median group (group 1) had a significant difference in leukocyte esterase activity between baseline and final examination and re-examination and final examination. In addition, patients in Group 1 had significantly lower BOP between baseline and final examination. While patients in the higher median group (group 2) showed a modest decrease in leukocyte esterase activity, which was significant only between baseline and final examination, no significant changes were observed concerning BOP. Furthermore, the associated systemic disease was observed in 30% and 81.2% of group 1 and 2 patients, respectively. CONCLUSION: The results suggest that leukocyte esterase activity in saliva measured by SillHa could serve as a reliable diagnostic marker for monitoring inflammatory status in periodontal disease.

Can the Leukocyte Esterase Strip Test Predict Persistence of Periprosthetic Joint Infection at Second-Stage Reimplantation?

BACKGROUND: We evaluated the reliability of intraoperative assessment of leukocyte esterase (LE) in synovial fluid samples from patients undergoing reimplantation following implant removal and spacer insertion for periprosthetic joint infection (PJI). Our hypothesis was that a positive intraoperative LE test would be a better predictor of persistent infection than either serum C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) or the combination of serum CRP and ESR. METHODS: The records of 76 patients who received a 2-stage exchange for PJI were retrospectively reviewed. Synovial fluid was collected for LE measurement during surgery before arthrotomy in 79 procedures. Receiver operating characteristic curves were generated. Sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and area under the curve (AUC) of LE, CRP, ESR, and CRP + ESR were calculated. RESULTS: Sensitivity, specificity, positive predictive value, and negative predictive value of the LE assay were 82%, 99%, 90%, and 97%, respectively. Receiver operating characteristic analysis revealed an LE threshold of 1.5 between the first (negative) and the second (positive) level of the ordinal variable, so that a grade starting from 1+ was accurate for a diagnosis of persistent infection (AUC 0.9044). The best thresholds for the CRP and the ESR assay were 8.25 mg/L (82% sensitivity, 84% specificity, AUC 0.8416) and 45 mm/h (55% sensitivity, 87% specificity, AUC 0.7493), respectively. CONCLUSION: The LE strip test proved a reliable tool to diagnose persistence of infection and outperformed the serum CRP and ESR assays. The strip test provides a valuable intraoperative diagnostic during second-stage revision for PJI.

A non-contact device for fast screening of wound infections.

Screening for wound infection relies on the expertise of the provider. Clinical diagnosis of infections based on wound swab/biopsy results often takes a few days and may not assess the full wound. There is a need for a non-invasive tool that can quickly and accurately diagnose wound infection. Leukocyte esterase strips are used to identify various infectious diseases. However, it is not clear whether infected wounds also have elevated leukocyte esterase activities as compared with non-infected wounds. To achieve the objective, a device was developed to detect elevated leukocyte esterase activities in wounds by measuring wound exudates adsorbed onto wound dressings in 3 minutes. The efficacy of the device in assessing leukocyte esterase activities across various chronic wounds was tested. Such measurements were unaffected by the type of underlying wound dressing. By correlating the device outputs with clinical adjudication of infection, we found that this device had high positive predictive values for diagnosing wound infection in a wide variety of chronic wounds. In addition, a positive device output increases the probability of detecting infected wounds, while the negative device output reduces the probability of detecting infected wounds. This rapid non-contact and disposable diagnostic tool may serve as a rapid and accurate indication of infection in the chronic wound.

Neutrophil gelatinase-associated lipocalin for urinary tract infection and pyelonephritis: a systematic review.

BACKGROUND: The sensitivity and specificity of the leukocyte esterase test are relatively low for a screening test for urinary tract infection (UTI). More accurate tests could reduce both overtreatment and missed cases. This study aimed to determine whether neutrophil gelatinase-associated lipocalin (NGAL) can replace leukocyte esterase in the diagnosis of UTI and/or whether NGAL accurately identifies children with acute pyelonephritis. METHODS: Data sources-MEDLINE and EMBASE. We only considered published studies that evaluated the results of an index test (NGAL) against the results of urine culture (for UTI) or against the results of dimercaptosuccinic acid (for acute pyelonephritis) in children aged 0 to 18 years. Two authors independently applied the selection criteria to all citations and independently extracted the data. RESULTS: A total of 12 studies met our inclusion criteria. Four studies (920 children) included data on NGAL for UTI; eight studies (580 children) included data on NGAL for pyelonephritis. We did not pool accuracy values because the included studies used different cutoff values. For the diagnosis of UTI, urinary NGAL appeared to have better accuracy than the leukocyte esterase test in all included studies. For the diagnosis of pyelonephritis, neither plasma NGAL nor urinary NGAL had high sensitivity and/or specificity. The number of studies was the main limitation of this systematic review. CONCLUSIONS: Urinary NGAL appears promising for the diagnosis of UTI; however, larger studies are needed to validate this marker as a replacement for leukocyte esterase. The use of NGAL for diagnosing acute pyelonephritis requires further study.

Clinical predictive value of the urine leukocyte esterase test positivity in childhood.

BACKGROUND: False negative or positive results may occur in the urine dipstick test for leukocyte esterase (LE), which is used to determine urinary tract infection (UTI). We aimed to investigate the clinical importance of the presence or absence of pyuria in urine sediment for diagnosing UTI in the presence of positive LE in dipstick analysis. METHODS: Patients admitted to the pediatric nephrology outpatient clinic with positive urine LE tests were divided into two groups: those without pyuria (Group 1) and those with pyuria (Group 2) in their urine sediment. Hospital files of the patients were evaluated retrospectively for demographic variables, lower or upper UTI symptoms, physical examination for phimosis and vulvovaginitis, urinalysis for LE and nitrite tests, urine sediment microscopy, urine culture, complete blood count and C-reactive protein. Both groups were compared for the significant growth of pathogenic bacteria in urine cultures along with clinical and laboratory parameters. RESULTS: Among 578 children giving samples for urinalysis, there were 287 cases with positive LE tests. Groups 1 and 2 included 123 and 164 cases, respectively. The proportion of girls was higher in Group 1 and vulvovaginitis rate was higher among the girls in Group 1. Girls with vulvovaginitis were mostly prepubertal. Upper UTI symptoms, significant pathogen growth rate, and elevated acute phase response were more common in Group 2. In addition, the phimosis rate was more common among the boys in Group 1 with false positive LE test. CONCLUSIONS: Children with positive LE tests without pyuria are mostly prepubertal girls and there is a high rate of vulvovaginitis in these girls. Unnecessary tests and treatments for UTI may be avoided with detailed history and physical examination in prepubertal girls who have a false positive LE test. We also found, for the first time, that a false positive LE test is significantly associated with phimosis in boys.

Leukocyte Esterase Versus ICM 2018 Criteria in the Diagnosis of Periprosthetic Joint Infection.

BACKGROUND: A leukocyte esterase (LE) test is inexpensive and provides real-time information about patients suspected of periprosthetic joint infections (PJIs). The 2018 International Consensus Meeting (ICM) recommends it as a diagnostic tool with a 2+ cutoff. There is still a lack of data revealing LE utility versus the ICM 2018 criteria for PJI. METHODS: This is a retrospective study of patients who underwent revision total hip and total knee arthroplasty at a single institution between March 2009 and December 2019. All patients underwent joint aspiration before the arthrotomy, and the LE strip test was performed on aspirated joint fluid. PJI was defined using the 2018 ICM criteria. RESULTS: As per the 2018 ICM criteria, 78 patients were diagnosed with chronic PJI and 181 were not infected. An LE test with a cutoff of ≥1+ had a sensitivity of 0.744, a specificity of 0.906, a positive predictive value of 0.773, an accuracy of 0.825 (95% confidence interval 0.772-0.878), and a negative predictive value of 0.891. The positive likelihood ratio (LR+) was 7.917. Using an LE cutoff of 2 + had a sensitivity of 0.513, a specificity of 1.000, and an accuracy of 0.756 (95% confidence interval-0.812). CONCLUSION: LE is a rapid and inexpensive test which can be performed at the bedside. Its performance is valuable as per ICM criteria. Based on the findings of this study and the given cohort, we suggest using the cutoff of LE1+ (result = negative or trace) as a point of care test to exclude infection, whereas LE at 2 + threshold has near absolute specificity for the diagnosis.

Leukocyte esterase test and alpha-defensin test have similar accuracy for the diagnosis of periprosthetic joint infection.

BACKGROUND: The diagnosis of periprosthetic joint infection (PJI) after total joint replacement remains challenging. Synovial biomarkers are recommended as the major diagnostic criteria for PJI. The purpose of this study was to test the accuracy of the alpha-defensin test and compare it with that of the leukocyte esterase (LE) test for the diagnosis of PJI. METHODS: We obtained 130 hip or knee aspirates from May 2015 to September 2018. PJI was defined according to the European Bone and Joint Infection Society (EBJIS) criteria. Synovial fluid samples were tested with the alpha-defensin ELISA and a LE strip. For the LE strip test, besides using the traditional threshold 500 (equal to ++), we are also using an improved one, with 500 (equal to ++) serving as the threshold for the tests before centrifugation and both 250 and 500 indicating positive results after centrifugation. The receiver operating characteristic (ROC) curves, sensitivity, specificity, positive predictive value, negative predictive value, and Cohen's Kappa value were calculated for the LE and alpha-defensin tests. RESULTS: The area under the curve (AUC) of alpha-defensin, LE strip test with traditional, and improved interpretation strategy were 0.875, 0.854, and 0.877, respectively. The Cohen's Kappa value for the alpha-defensin tests was 0.826 with the traditional LE interpretation strategy and 0.875 with the improved strategy. CONCLUSION: The present study shows that the use of the LE strip to test synovial fluid yielded an accuracy similar to that of the alpha-defensin immunoassay for the diagnosis of PJI; this finding supports the 2018 ICM PJI definition, which considers positive alpha-defensin and LE test results to be equivalent.

Quantitative urine test strip reading for leukocyte esterase and hemoglobin peroxidase.

BACKGROUND: Recently, urine test strip readers have become available for automated test strip analysis. We explored the possibilities of the Sysmex UC-3500 automated urine chemistry analyzer based on complementary metal oxide semiconductor (CMOS) sensor technology with regard to accuracy of leukocyte esterase and hemoglobin peroxidase results. We studied the influence of possible confounders on these measurements. METHODS: Reflectance data of leukocyte esterase and hemoglobin peroxidase were measured using CMOS technology on the Sysmex UC-3500 automated urine chemistry analyzer. Analytical performance (imprecision, LOQ) as well as the correlation with white blood cell (WBC) and red blood cell (RBC) counts (Sysmex UF-5000) were studied. Furthermore, the influence of urinary dilution, haptoglobin, pH and ascorbic acid as confounders was determined. RESULTS: Within- and between-run imprecision (reflectance signal) ranged from 1.1% to 3.6% and 0.9% to 4.2% for peroxidase and 0.4% to 2.5% and 0.4% to 3.3% for leukocyte esterase. Good agreement was obtained between the UF-5000 for RBCs and peroxidase reflectance (r=0.843) and for WBCs and leukocyte esterase (r=0.821). Specific esterase activity decreased for WBC counts exceeding 100 cells/µL. Haptoglobin influenced the peroxidase activity, whereas leukocyte esterase and peroxidase activities showed a pH optimum between 5.0 and 6.5. A sigmoidal correlation was observed between urinary osmolality and peroxidase activity. CONCLUSIONS: CMOS technology allows to obtain high quality test strip results for assessing WBC and RBC in urine. Quantitative peroxidase and leukocyte esterase are complementary with flow cytometry and have an added value in urinalysis, which may form a basis for expert system development.

A meta-analysis of synovial biomarkers in periprosthetic joint infection: Synovasure™ is less effective than the ELISA-based alpha-defensin test.

PURPOSE: (1) To determine the overall accuracy of synovial alpha-defensin, synovial C-reactive protein (sCRP), interleukin-6 (sIL-6), and leukocyte esterase (sLE) as diagnostic markers for periprosthetic joint infection (PJI) and (2) to independantly evaluate the accuracy of both the laboratory-based ELISA alpha-defensin test and the Synovasure™ alpha-defensin test kit. METHODS: An EMBASE and MEDLINE (PubMed) database search was performed using a set of professionally set search terms. Two independent reviewers rated eligible articles. Sensitivity and specificity were meta-analysed using a bivariate random-effects model. RESULTS: Accuracy values were extracted from 42 articles. Pooled sensitivity and specificity of the represented biomarkers were: alpha-defensin ELISA 0.97 (95% CI 0.91-0.99) and 0.97 (95% CI 0.94-0.98), respectively; Synovasure™ test kit assay 0.80 (95% CI 0.65-0.89) and 0.89 (95% CI 0.76-0.96), respectively; sLE 0.79 (95% CI 0.67-0.87) and 0.92 (95% CI 0.87-0.92), respectively; sIL-6 0.76 (95% CI 0.65-0.84) and 0.91 (95% CI 0.88-0.94), respectively; sCRP 0.86 (95% CI 0.81-0.91) and 0.90 (95% CI 0.86-0.93), respectively. CONCLUSION: The labararory-based alpha-defensin ELISA test showed the highest ever reported accuracy for PJI diagnosis. However, this did not apply for the Synovasure™ alpha-defensin test, which was comparable in its overall diagnostic accuracy to sCRP, sIL-6 and sLE. The later biomarkers also did not yield an overall diagnostic accuracy higher than that previously reported for synovial white cell count (sWBC) or culture bacteriology. Based on current evidence, no synovial biomarker should be applied as a standalone diagnostic tool. Furthermore, the use of the laboratory-based alpha-defensin ELISA test should be encouraged, still, the Synovasure™ alpha-defensin test kit should be critically appreciated. LEVER OF EVIDENCE: III.

Centrifugation May Change the Results of Leukocyte Esterase Strip Testing in the Diagnosis of Periprosthetic Joint Infection.

BACKGROUND: Centrifugation is used to remove the color interference by erythrocytes in blood-synovial fluid samples before leukocyte esterase (LE) strip testing. However, the impact of centrifugation requires further study. METHODS: From April 2016 to October 2017, 133 (53 infected and 80 noninfected) patients were included in this study. One drop of synovial fluid was applied to LE strips before and after centrifugation in 110 cases. The other 23 cases could not be read without centrifugation due to the color disturbance caused by blood contamination. The results were recorded after approximately 3 minutes according to different color grades on a color chart, including grade 3 (++), grade 2 (+), and grade 1 (others). RESULTS: After centrifugation, almost every sample was lighter in color than before. Although most results changed inconspicuously and remained in the same grade, 18.6% (8/43) and 17.9% (12/67) of cases were downgraded in the periprosthetic joint infection and non-periprosthetic joint infection groups, respectively. Before centrifugation, when grade 3 (++) was used as the positive threshold, the sensitivity and specificity were 97.7% (86.2%-99.9%) and 100% (94.3%-100%), respectively. After centrifugation, when grades 2 and 3 (+ and ++, respectively) were used as the positive threshold, the sensitivity and specificity were 92.5% (80.9%-97.6%) and 100% (94.3%-100%), respectively. CONCLUSIONS: The influence of centrifugation should be considered when interpreting the LE strip test results. For cases without centrifugation, we recommended using ++ as the positive threshold, while for cases using centrifugation, the threshold should be reduced to both ++ and +.

The Leukocyte Esterase Test Strip Is a Poor Rule-Out Test for Periprosthetic Joint Infection.

BACKGROUND: The urinary leukocyte esterase (LE) test strip has been suggested as a good screening test for periprosthetic joint infection (PJI). The purpose of this study is to compare the diagnostic profile of LE assays from different manufacturers and determine whether the LE test strip is a good rule-out test. METHODS: Synovial fluid samples (N = 344), sent to 1 laboratory for PJI testing, were used in this prospective study. Four different tests for synovial fluid LE were simultaneously evaluated for their performance in detecting white blood cell (WBC) positive samples (>3000 cells/µL). RESULTS: Both neutrophil elastase immunoassays demonstrated greater sensitivity than urinary LE test strips (92.0% and 90.8% vs 72.4% and 80.3%; all P < 0.011). Fifty-three percent of false-negative urinary LE test strip results clearly missed the presence of elevated levels of synovial fluid LE. Invalid urinary LE test strip results were 4-fold more likely among WBC (+) compared with WBC (-) samples (27.0% vs 6.8%; P < 0.0001). The combined failure to detect an elevated WBC count, because of either false-negative or invalid results, was 47.1% and 41.4% for the Roche and Siemens test strips, respectively. CONCLUSIONS: This study agrees with the existing literature demonstrating that the LE test strips are among the lowest sensitivity tests for PJI. The urinary LE tests strips should not be used to rule-out PJI, as they often fail to detect abundant levels of LE in synovial fluid. Instead, it is more appropriate to use the (++) LE test strip result as a secondary confirmatory rule-in test for PJI because of its high specificity.

Diagnosing Periprosthetic Joint Infection: And the Winner Is?

BACKGROUND: Diagnosis of periprosthetic joint infection (PJI) remains a challenge despite a wide variety of available diagnostic tests. The question that arises is which of these tests has a better performance for diagnosing PJI. Diagnostic odds ratio (DOR) has been described as the best indicator for test performance. METHODS: To compare the performance of the standard diagnostic tests, the DOR of serum erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), synovial fluid (SF) white blood cell (WBC) count, SF polymorphonuclear (PMN%), and leukocyte esterase (LE) were calculated. RESULTS: We obtained 4662 ESRs, 4392 CRPs, 836 SF WBC, 804 SF PMN%, and 659 LE results. LE had the highest DOR for diagnosing PJI: 30.06 (95% confidence interval [CI]: 17.8-50.7). The rest of the DORs in the descending order were SF WBC: 29.4 (95% CI: 20.2-42.8), CRP: 25.6 (95% CI: 19.5-33.7), SF PMN%: 25.5 (95% CI: 17.5-37.0), and ESR: 14.6 (95% CI: 11.5-18.6). CONCLUSION: Based on our findings, it appears that among the minor diagnostic criteria, LE has the best performance.

Determining False Positive Rates of Leukocyte Esterase Reagent Strip When Used as a Detection Tool for Joint Infection.

BACKGROUND: Use of leukocyte esterase (LE) testing of synovial fluid as an adjunct to the infection workup in total joint arthroplasty patients has been advocated. The purpose of this study was to determine the false positive rate of this test. METHODS: Two hundred patients with the diagnosis of degenerative osteoarthritis undergoing a total knee arthroplasty were identified for this study. The knee joint was aspirated under sterile conditions before performing the total knee arthroplasty. The fluid was analyzed with an LE reagent strip. RESULTS: There were 27 bloody and 17 dry aspirations. One hundred forty-nine patients produced an aspiration that allowed for LE testing. There was 1 positive LE result. The specificity of the LE test was found to be 99.3%. CONCLUSION: These data suggest the LE strip as a part of the workup for infection in a native knee should yield few false positive results.

Leukocyte Esterase Strip Test Can Predict Subsequent Failure Following Reimplantation in Patients With Periprosthetic Joint Infection.

BACKGROUND: Leukocyte esterase (LE) strip test is an accurate marker for diagnosing periprosthetic joint infection (PJI). This study aims to determine if LE is a good predictor of persistent infection and/or subsequent failure in patients undergoing reimplantation. METHODS: This single-institution study prospectively recruited and retrospectively analyzed 109 patients who underwent two-stage exchange treatment of PJI, from 2009-2016, and had an LE test performed at time of reimplantation. LE results of "2+" were considered positive. Ninety-five patients had 90-day minimum follow-up to assess treatment failure, defined by Delphi criteria. Eighteen patients were excluded due to blood contamination of LE test, resulting in a final cohort of 77 patients (mean follow-up 1.76 years). RESULTS: Of the final cohort, 19 patients (24.7%) experienced subsequent failure. At reimplantation, LE test was positive in 22.2% of culture-positive and 4.4% of culture-negative cases. The LE test was negative in all patients who had not failed at latest follow-up, yielding sensitivity, specificity, positive predictive value, negative predictive value, and AUC of 26.3%, 100%, 100%, 87.5%, and 0.632, respectively; in comparison, MSIS criteria respectively yielded 25.0%, 87.3%, 27.6%, 85.8%, and 0.562 (P = .01 for specificity). Kaplan-Meier curves revealed higher failure rate in patients who had a positive LE test at time of reimplantation (P < .001). CONCLUSION: There is a dire need for an accurate diagnostic test to determine optimal timing of reimplantation in patients undergoing surgical treatment for PJI. The current study suggests that a positive LE test may be indicative of persistence of infection and results in a higher rate of subsequent failure.

Interpretation of Leukocyte Esterase for the Detection of Periprosthetic Joint Infection Based on Serologic Markers.

BACKGROUND: Leukocyte esterase (LE) is a rapid, point-of-care test for periprosthetic joint infection. The purpose of this study was to provide a tool for interpreting LE based on an initial serologic screening. METHODS: We reviewed the records of 319 patients who had erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) screening before hip or knee aspiration; 102 had elevated ESR and CRP levels, 64 had an elevated ESR or CRP level, and 153 had normal serology. The likelihood of infection was calculated based on the results of LE testing. RESULTS: When LE results were concordant with ESR and CRP levels, LE served to effectively diagnose or rule out a diagnosis of periprosthetic joint infection with >95% certainty. When LE was discordant from serology, only the stricter LE thresholds (2+ or negative) were adequately diagnostic to potentially suggest a change in clinical decision-making. CONCLUSION: With discordant results, the lesser thresholds (1+ or trace) should serve to incite further diagnostic inquiry.

The Leukocyte Esterase Strip Test has Practical Value for Diagnosing Periprosthetic Joint Infection After Total Knee Arthroplasty: A Multicenter Study.

BACKGROUND: Leukocyte esterase (LE) was recently reported to be an accurate marker for diagnosing periprosthetic joint infection (PJI) as defined by the Musculoskeletal Infection Society (MSIS) criteria. However, the diagnostic value of the LE test for PJI after total knee arthroplasty (TKA), the reliability of the subjective visual interpretation of the LE test, and the correlation between the LE test results and the current MSIS criteria remain unclear. METHODS: This study prospectively enrolled 60 patients undergoing revision TKA for either PJI or aseptic failure. Serological marker, synovial fluid, and histological analyses were performed in all cases. The PJI group comprised 38 cases that met the MSIS criteria and the other 22 cases formed the aseptic group. All the LE tests were interpreted using both visual judgment and automated colorimetric reader. RESULTS: When "++" results were considered to indicate a positive PJI, the sensitivity, specificity, positive and negative predictive value, and diagnostic accuracy were 84, 100, 100, 79, and 90%, respectively. The visual interpretation agreed with the automated colorimetric reader in 90% of cases (Cronbach α = 0.894). The grade of the LE test was strongly correlated with the synovial white blood cell count (ρ = 0.695) and polymorphonuclear leukocyte percentage (ρ = 0.638) and moderately correlated with the serum C-reactive protein and erythrocyte sedimentation rate. CONCLUSION: The LE test has high diagnostic value for diagnosing PJI after TKA. Subjective visual interpretation of the LE test was reliable and valid for the current battery of PJI diagnostic tests according to the MSIS criteria.