Leukocyte Esterase From Synovial Fluid Aspirate
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Synovial fluid biomarkers have demonstrated diagnostic accuracy surpassing the currently used diagnostic tests for periprosthetic joint infection (PJI).The purpose of this study is to directly compare the sensitivity and specificity of the synovial fluid α-defensin immunoassay to the leukocyte esterase (LE) colorimetric test strip.Synovial fluid was collected from 46 patients meeting the inclusion criteria of this prospective diagnostic study. Synovial fluid samples were tested with both a novel synovial-fluid-optimized immunoassay for α-defensin and the LE colorimetric test strip. The Musculoskeletal Infection Society (MSIS) definition was used to classify 23 periprosthetic infections and 23 aseptic failures; this classification was used as the standard against which the two diagnostic tests were compared.The synovial fluid α-defensin immunoassay correctly predicted the MSIS classification of all patients in the study, demonstrating a sensitivity and specificity of 100% for the diagnosis of PJI. The α-defensin assay could be read for all samples, including those with blood in the synovial fluid. The leukocyte esterase test strip could not be interpreted in eight of 46 samples (17%) as a result of blood interference. Analysis of the LE strips that could be interpreted yielded a sensitivity of 69% and a specificity of 100%.The synovial fluid α-defensin immunoassay outperformed the LE colorimetric test strip in this study and provided reliable results even when the LE test strip failed as a result of blood interference. The simple analytic results provided by the α-defensin immunoassay, compared with the more complex and interpretive nature of both the MSIS criteria and LE colorimetric test strip, make it a highly attractive diagnostic tool.Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.
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Erythrocyte sedimentation rate
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Diagnosis of chronic prosthetic joint infection (PJI) is often challenging. Painful prosthesis is frequently due to an infection but to diagnose it is somethimes difficult. All recent guidelines stress the central role of joint punction in diagnosis of PJI if the infection is not demonstrated. However which test on synovial fluid must be carried out is not so clearly defined. Total white blood cell count and differential leukocite count are usually considered useful in diagnosis but cut offs reported by different studies are quite different. Moreover this test needs a relatively large amount of fluid and blood contamination of it largely affects the result. What9s more the synovial fluid WBC count may be unreliable in the setting of a metal-on-metal bearing or corrosion reaction. Routine cultures should be maintained between 5 and 14 days, their sensitivity appears low in chronic infection even if witholding antimicrobial therapy before the collection of the fluid can increase the likelihood of recovery an organism. Synovial leukocyte esterase can be performed as a rapid office or intraoperative point of care test using urinalysis strips. It is cheap and easy to perform, but the presence of blood in the sample can affect the result and it needs centrifugation. Recently a new test has been proposed to detect alfa-defensine in synovial fluid. It shows a high sensitivity and an exellent specificity. We performed 25 joint punctions on 25 patients with suspected PJI (enrollment is going on). Synovial fluid collected was tested for: leukocite esterase, WBC count and differential, colture in blood colture bottle for anerobe and aerobes (BacT/ALERT Biomerieux, inc) and detection of alfa-defensine level (Synovasure – Zimmer) In patients who underwent surgery at least 5 samples of periprotesic tissue were collected for microbiologic analysis and the removed implant was sonicated according with the methodic. Furthermore samples for frozen section were sent and a histologic examination was made according to the Moriewitz – Kerr classification. The MSIS criteria was utilized to classify the case as infected or not.
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The incidences of periprosthetic fracture and periprosthetic joint infection after total hip arthroplasty are expected to increase exponentially over the coming decades. Epidemiologic data suggest that many periprosthetic fractures after THA occur concurrently with a loose femoral implant. Recent studies suggest an approximately 8% incidence of indolent infection in cases of suspected aseptic loosening. The available data, therefore, suggest that periprosthetic fracture and infection may coexist, and this possibility should be considered, particularly in patients with a loose femoral stem and high pretest possibility. Although currently limited, the available literature provides some guidance as how to manage this complex issue.
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Background
The analysis of synovial fluid is an important tool for diagnosing joint disease. When synovial fluid is removed, the white cell count (WCC) decreases with time, and an inflammatory liquid could become a false non-inflammatory specimen. Reagent strip testing of urine is a valid tool for the diagnosis of urinary tract infection, via the detection of leukocyte esterase activity. It has been used for the analysis of others body fluids. Synovial fluid test at the site of arthrocentesis using reagent strips could have potential benefits as a screening tool.Objectives
To evaluate the performance of leukocyte esterase reagent strips for diagnosis of inflammatory synovial fluid.Methods
Prospective single center study. We analyzed synovial fluids samples collected from patients in a tertiary university Hospital (November 2015- December 2016). Synovial fluid samples were tested within 1 hour after collection. We analyzed: The presence of leukocyte esterase using the leukocyte esterase reagent strips test (originally designed for urine test, URI-Clip Test, Menarini Diagnostics). It was recorded semi quantitatively: negative, 1+ (>25 WBC/uL), 2+ (>75 WBC/uL) or 3 +(>500 WBC/uL) by comparison with a standard color chart found on the container9s label. The WCC, formula, glucose level. The WCC was measured by manual leukocyte counting, using saline as diluents. Cultures were also collected. We consider + if leucocyte esterase pad was more or equal than 1+ positive. The cut-off for the WCC (>2000cells/mm3) was used to differentiate between inflammatory and non-inflammatory specimens. We compared the WCC (reference standard diagnostic test) with the presence of leukocyte esterase using the leukocyte esterase reagent. Sensitivity (Se), specificity (Sp), PPV, NPV were determined. P-value smaller than 0.05 were considered significant.Results
During the study period, 125 joint fluid specimens were analyzed: 56 (44.8%) mechanical and 69 (55.2%) inflammatory. Of the mechanical fluids 33 (58.9%) were negative by leukocyte esterase reagent and of the inflammatory fluids 67 (97.1%) were positive. The Se and Sp of leukocyte esterase reagent was 97.1% and 58.9% respectively. The PPV was 74.4% and NPV was 94.3%. The 2 false-negative results (negative by leukocyte esterase reagent but more than 2000 WBC/mm3), showed a predominance of mononuclears (> =91%), the median WCC was 2 775/mm and median neutrophil percentage was 8.5%. For inflammatory fluids: semi-quantitative results (negative, 1+, 2+ and 3+) were significantly different regarding the main leukocyte, neutrophil and lymphocyte count (table).Conclusions
Our results demonstrate that leukocyte esterase reagent strips are a rapid, cheap, and sensitive tool to identify inflammatory synovial fluid. Leukocyte esterase reagent strips had an excellent Se but a poor Sp, it could be used as a screening tool in primary care practice. A positive result may indicate an inflammatory process, then the patient should be referred to a rheumatologist.Disclosure of Interest
None declaredLeukocyte esterase
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Periprosthetic joint infection continues to frustrate the medical community. Although the demand for total joint arthroplasty is increasing, the burden of such infections is increasing even more rapidly, and they pose a unique challenge because their accurate diagnosis and eradication can prove elusive. This review describes the current knowledge regarding diagnosis and treatment of periprosthetic joint infection. A number of tools are available to aid in establishing a diagnosis of periprosthetic joint infection. These include the erythrocyte sedimentation rate, serum C-reactive protein concentration, synovial white blood-cell count and differential, imaging studies, tissue specimen culturing, and histological analysis. Multiple definitions of periprosthetic joint infection have been proposed but there is no consensus. Tools under investigation to diagnose such infections include the C-reactive protein concentration in the joint fluid, point-of-care strip tests for the leukocyte esterase concentration in the joint fluid, and other molecular markers of periprosthetic joint infection. Treatment options include irrigation and debridement with prosthesis retention, one-stage prosthesis exchange, two-stage prosthesis exchange with intervening placement of an antibiotic-loaded spacer, and salvage treatments such as joint arthrodesis and amputation. Treatment selection is dependent on multiple factors including the timing of the symptom onset, patient health, the infecting organism, and a history of infection in the joint. Although prosthesis retention has the theoretical advantages of decreased morbidity and improved return to function, two-stage exchange provides a lower rate of recurrent infection. As the burden of periprosthetic joint infection increases, the orthopaedic and medical community should become more familiar with the disease. It is hoped that the tools currently under investigation will aid clinicians in diagnosing periprosthetic joint infection in an accurate and timely fashion to allow appropriate treatment. Given the current knowledge and planned future research, the medical community should be prepared to effectively manage this increasingly prevalent disease.
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PURPOSE: Septic arthritis, bacterial infection of the joint space, is an orthopedic emergency and requires prompt antibiotics and joint decompression with irrigation and drainage. Poor sensitivity characterizes current testing available to the Emergency Clinician, including systemic leukocytosis (50%), blood culture (25-50%) gram stain (30% to 70%) and synovial leukocytosis of 50,000 (70%). Recently, orthopedic research has begun to explore utilization of leukocyte esterase assays as an additional investigation for septic arthritis. No previous study has examined the utility and feasibility of leukocyte esterase in a community Emergency Department. METHODS: In this prospective study, patients who underwent joint aspiration with joint fluid culture underwent synovial leukocyte esterase testing. Diagnosis of septic arthritis was confirmed if one of the following is found: 1) a positive synovial fluid culture; 2) pathogen isolated from blood culture and clinical presentation deemed consistent with septic arthritis; or 3) turbid synovial fluid with a negative crystal analysis result. RESULTS: 23 joint aspirations were performed from March through December of 2020, of which 5 were diagnosed with septic arthritis. 4 had readable leukocyte esterase tests and all 4 resulted in positive tests, indicating sensitivity of 100%. The fifth was unreadable due to excess blood in the sample. Of the remaining 18 samples, 16 were readable and 6 had a positive leukocyte esterase, indicating specificity of 63%. Notably, synovial leukocytosis demonstrated sensitivity of 25% and specificity of 86% and Gram stain demonstrated sensitivity of 60% and specificity of 100%. CONCLUSIONS: This study suggests that synovial fluid leukocyte esterase is an effective tool in the hands of the Emergency Clinician that, when readable, has superior sensitivity for septic joint than other testing available based on both results from this study and from existing literature. This case series also demonstrates pathologies besides septic joint that resulted positive leukocyte esterase test and the ease with which this test was implemented in a community emergency department. Given these results and its cost-effectiveness (roughly 50¢), this study demonstrates potential for more widespread use of synovial leukocyte esterase testing.
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Leukocytosis
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Monoarthritis
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