Q.-Y. Zheng, J.-Y. Sun, J.-C. Li, Medical School of Chinese People's Liberation Army General Hospital, Beijing, China.
Q.-Y. Zheng, M. Ni, P. Ren, Q.-B. Ji, J.-Y. Sun, J-C. Li, J.-Y. Chen, G.-Q. Zhang, Department of Orthopedics, the First Medical Center, Chinese People's Liberation Army General Hospital, Beijing, China.
Clin Orthop Relat Res. 2021 Jun 1;479(6):1323-1330. doi: 10.1097/CORR.0000000000001609.
The leucocyte esterase (LE) strip test often is used to diagnose periprosthetic joint infection (PJI). In accordance with the manufacturer's directions, the LE strip test result is read 3 minutes after exposing it to joint fluid, but this has not been supported by robust research. Moreover, we have noted that the results of the LE strip test might change over time, and our previous studies have found that centrifugation causes the results of the LE strip test to degrade. Still, there is no evidence-based recommendation as to when to read the LE strip test to maximize diagnostic accuracy, in general, and the best reading times for the LE strip test before and after centrifugation need to be determined separately, in particular.
QUESTIONS/PURPOSES: (1) What is the optimal timing for reading LE strip test results before centrifugation to diagnose PJI? (2) What is the optimal timing for reading LE strip test results after centrifugation to diagnose PJI?
This study was a prospective diagnostic trial. In all, 120 patients who were scheduled for revision arthroplasty and had signs of infection underwent joint aspiration in the outpatient operating room between July 2018 and July 2019 and were enrolled in this single-center study. For inclusion, patients must have had a diagnosis of PJI or nonPJI, valid synovial fluid samples, and must not have received antibiotics within 2 weeks before arthrocentesis. As such, 36 patients were excluded; 84 patients were included for analysis, and all 84 patients agreed to participate. The 2018 International Consensus Meeting Criteria (ICM 2018) was used for the classification of 49 patients with PJI (score ≥ 6) and 35 without PJI (score ≤ 2). The classification was used as the standard against which the different timings for reading LE strips were compared. All patients without PJI were followed for more than 1 year, during which they did not report the occurrence of PJI. All patients were graded against the diagnostic criteria regardless of their LE strip test results. In 83 patients, one drop of synovial fluid (50 μL) was applied to LE strips before and after centrifugation, and in one patient (without PJI), the sample was not centrifuged because the sample volume was less than 1.5 mL. The results of the strip test were read on an automated colorimeter. Starting from 1 minute after centrifugation, these strips were automatically read once every minute, 15 times (over a period of 16 minutes), and the results were independently recorded by two observers. Results were rated as negative, ±, 1+, and 2+ upon the machine reading. Grade 2+ (dark purple) was used as the threshold for a positive result. An investigator who was blinded to the study performed the statistics. Optimal timing for reading the LE strip before and after centrifugation was determined by using receiver operative characteristic (ROC) analysis. The specificity, sensitivity, and positive predictive and negative predictive values were calculated for key timepoints.
Before centrifugation, the area under the curve was the highest when the results were read at 5 minutes (0.90 [95% CI 0.83 to 0.98]; sensitivity 0.88 [95% CI 0.75 to 0.95]; specificity 0.89 [95% CI 0.72 to 0.96]). After centrifugation, the area under the curve was the highest when the results were read at 10 minutes (0.92 [95% CI 0.86 to 0.98]; sensitivity 0.65 [95% CI 0.50 to 0.78]; specificity 0.97 [95% CI 0.83 to 1.00]).
The LE strip test results are affected by time and centrifugation. For samples without centrifugation, we found that 5 minutes after application was the best time to read LE strips. We cannot deny the use of centrifuges because this is an effective way to solve the sample-mingling problem at present. We recommend 10 minutes postapplication as the most appropriate time to read LE strips after centrifugation. Multicenter and large-sample size studies are warranted to further verify our conclusion.
Level II, diagnostic study.
白细胞酯酶（LE）条带试验常用于诊断假体周围关节感染（PJI）。根据制造商的说明，在将 LE 条带试验暴露于关节液后 3 分钟读取结果，但这并没有得到强有力的研究支持。此外，我们注意到 LE 条带试验的结果可能会随时间变化，我们之前的研究发现离心会导致 LE 条带试验的结果降解。然而，目前尚无关于何时读取 LE 条带试验以最大程度提高诊断准确性的循证建议，一般来说，需要分别确定离心前和离心后读取 LE 条带试验的最佳时间，特别是。
问题/目的：（1）在离心前读取 LE 条带试验结果以诊断 PJI 的最佳时间是什么？（2）在离心后读取 LE 条带试验结果以诊断 PJI 的最佳时间是什么？
本研究为前瞻性诊断试验。共有 120 名计划接受翻修关节置换术且有感染迹象的患者在 2018 年 7 月至 2019 年 7 月期间在门诊手术室接受关节抽吸，并纳入本单中心研究。纳入标准为患者必须有 PJI 或非 PJI 的诊断、有效的滑膜液样本，并且在关节穿刺前 2 周内未使用抗生素。因此，有 36 名患者被排除在外；84 名患者符合条件进行分析，所有 84 名患者均同意参与。使用 2018 年国际共识会议标准（ICM 2018）对 49 名 PJI 患者（评分≥6）和 35 名无 PJI 患者（评分≤2）进行分类。分类结果作为标准，与不同时间读取 LE 条带的结果进行比较。所有无 PJI 的患者均随访超过 1 年，在此期间他们均未报告发生 PJI。所有患者均根据诊断标准进行分级，无论其 LE 条带试验结果如何。在 83 名患者中，有 1 滴滑膜液（50 μL）在离心前后应用于 LE 条带，在 1 名患者（无 PJI）中，由于样本量小于 1.5 mL，因此未进行离心。使用自动比色计读取条带试验结果。从离心后 1 分钟开始，每隔 1 分钟自动读取 15 次（16 分钟），并由两名观察者独立记录结果。机器读数结果为阴性、±、1+和 2+。使用 2+（深紫色）作为阳性结果的阈值。一位对研究不知情的研究人员进行了统计学分析。通过使用接受者操作特征（ROC）分析确定离心前后读取 LE 条带的最佳时间。计算了关键时间点的特异性、敏感性、阳性预测值和阴性预测值。
在离心前，当结果在 5 分钟时读取时，曲线下面积最高（0.90 [95%CI 0.83 至 0.98]；敏感性 0.88 [95%CI 0.75 至 0.95]；特异性 0.89 [95%CI 0.72 至 0.96]）。离心后，当结果在 10 分钟时读取时，曲线下面积最高（0.92 [95%CI 0.86 至 0.98]；敏感性 0.65 [95%CI 0.50 至 0.78]；特异性 0.97 [95%CI 0.83 至 1.00]）。
LE 条带试验结果受时间和离心的影响。对于未经离心的样本，我们发现应用后 5 分钟是读取 LE 条带的最佳时间。我们不能否认使用离心机，因为这是目前解决样本混合问题的有效方法。我们建议在离心后 10 分钟应用时读取 LE 条带。需要进行多中心和大样本量的研究来进一步验证我们的结论。
二级，诊断研究。
