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The Leukocyte Esterase Test Strip Is a Poor Rule-Out Test for Periprosthetic Joint Infection
Carl A Deirmengian1, Lihua Liang2, John P Rosenberger2
1Department of Orthopaedic Surgery, The Rothman Institute, Thomas Jefferson University, Philadelphia, Pennsylvania.
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.
Insights
Urinary leukocyte esterase (LE) test strips are not sensitive enough to rule out periprosthetic joint infection (PJI). These tests often miss elevated LE levels in synovial fluid, making them unreliable for excluding PJI.
Area of Science:
- Orthopedics
- Infectious Diseases
- Clinical Diagnostics
Background:
- Periprosthetic joint infection (PJI) diagnosis relies on sensitive and specific tests.
- Urinary leukocyte esterase (LE) test strips are proposed as a screening tool for PJI.
- The diagnostic accuracy of LE test strips from various manufacturers needs evaluation.
Purpose of the Study:
- To compare the diagnostic performance of LE assays from different manufacturers.
- To determine the utility of urinary LE test strips as a rule-out test for PJI.
Main Methods:
- Prospective study of 344 synovial fluid samples sent for PJI testing.
- Simultaneous evaluation of four different synovial fluid LE tests.
- Comparison of LE test results with white blood cell (WBC) counts (>3000 cells/µL).
Main Results:
- Neutrophil elastase immunoassays showed higher sensitivity (90.8%-92.0%) than urinary LE test strips (72.4%-80.3%).
- Urinary LE test strips yielded false-negative results in 53% of cases with elevated synovial fluid LE.
- Invalid results were more common in WBC-positive samples (27.0% vs 6.8%), leading to a combined failure rate of 41.4%-47.1%.
Conclusions:
- Urinary LE test strips have low sensitivity for PJI detection.
- These strips are unreliable for ruling out PJI due to frequent false negatives and invalid results.
- Positive LE test strip results (++) may serve as a secondary confirmatory test for PJI due to high specificity.
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