Use of leucocyte esterase reagent strips in the diagnosis or exclusion of prosthetic joint infection

Abstract

Infection is a leading indication for revision arthroplasty. Established criteria used to diagnose prosthetic joint infection (PJI) include a range of laboratory tests. Leucocyte esterase (LE) is widely used on a colorimetric reagent strip for the diagnosis of urinary tract infections. This inexpensive test may be used for the diagnosis or exclusion of PJI. Aspirates from 30 total hip arthroplasties (THAs) and 79 knee arthroplasties (KA) were analysed for LE activity. Semi-quantitative reagent strip readings of 15, 70, 125 and 500 white blood cells (WBC) were validated against a manual synovial white cell count (WCC). A receiver operating characteristic (ROC) curve was constructed to determine the optimal cut-off point for the semi-quantitative results. Based on established criteria, six THAs and 15 KAs were classified as infected. The optimal cut-off point for the diagnosis of PJI was 97 WBC. The closest semi-quantitative reading for a positive result was 125 WBC, achieving a sensitivity of 81% and a specificity of 93%. The positive and negative predictive values of the LE test strip were 74% and 95% respectively. The LE reagent strip had a high specificity and negative predictive value. A negative result may exclude PJI and negate the need for further diagnostic tests.

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

“…This observation was first made by Parvizi et al [6], finding that 11.6% (17 of 147) of samples were unreadable because of blood. Subsequent studies verified this rate of invalid results, finding invalid test strip rates of 29.2% [7], 17% [5], and 9.5% [1]. Because of the high rate of blood interference, it has been suggested that the sample is centrifuged to remove blood cells before the fluid is placed on the test strip [12].…”

“…The original report on the utility of LE by Parvizi et al [6] found that a (þþ) LE cutoff provided 80.6% sensitivity in diagnosing PJI. Although there are a few centers reporting a higher sensitivity for the urinary LE test strip [10,11], most centers have reported lower values, including sensitivities of 69% [5], 66% [9], 81% [1], 84.21% [2], 75% [3], and 84% [4]. A recent large retrospective study of tests for PJI including the erythrocyte sedimentation rate, C-reactive protein, WBC count, polymorphonuclear neutrophil percentage, and LE found that LE had the lowest sensitivity of all tests [3].…”

“…The arthroplasty literature has recently suggested considering the use of the urinary LE test strip for the purposes of screening synovial fluid for periprosthetic joint infection (PJI) [1]. However, the performance of the LE test strip in synovial fluid has demonstrated suboptimal diagnostic characteristics for PJI.…”

“…However, the performance of the LE test strip in synovial fluid has demonstrated suboptimal diagnostic characteristics for PJI. In fact, research on the use of the urinary LE test strip to screen synovial fluid has revealed 3 serious concerns: (1) several institutions have demonstrated a low LE test strip sensitivity for PJI [1e6], (2) several institutions have reported on a high rate of uninterpretable results because of the presence of blood [1,5e7], and (3) the optimal cutoff for LE test strip positivity in synovial fluid has varied between institutions [6,7]. These are the type of issues that need to be accounted for when validating an off-label use of a diagnostic test.…”

Diagnostik der periprothetischen Gelenkinfektion bei Schulterendoprothesen

“…Weiterhin kann in das Gelenkpunktat ein Leukozytenesteraseteststreifen gehalten werden, wie es für den Urinstatus bekannt ist. Für die Diagnostik am Knie-und Hüftgelenk werden Sensitivitäten zwischen 69 und 81 % sowie Spezifitäten zwischen 93 und 100 % angegeben [27][28][29]. Allerdings waren zwischen 17 und 30 % der Proben aufgrund von Blutbeimengungen des Punktats nicht ablesbar.…”