EFFECTIVENESS OF URINARY LEUKOCYTE TEST STRIPS FOR PERITONITIS SCREENING

Introduction:

Rapid diagnosis and treatment of peritoneal dialysis related peritonitis (PDRP) is critical as this complication is associated with significant morbidity, including catheter loss, ultrafiltration failure, irreversible peritoneal membrane damage, and transition to hemodialysis. We assessed the effectiveness of urinary leukocyte test strips, originally designed for detecting urinary tract infections, for PDRP screening.

Methods:

A total of 162 spent PD effluent (PDE) samples were collected from 30 patients, with dwell times ranging from 30 to 615 minutes. Samples were kept cool with ice packs and transported to the lab within 48 hours. White blood cell (WBC) count was measured using the Horiba Pentra XL80 with or without prior cell concentration, depending on the WBC amount. Samples were then aliquoted and stored at -80°C until analysis.

For the negative control (NC), we prepared a buffer containing 1.06% dextrose by mixing 4.25% dextrose DELFLEX® (Fresenius Medical Care, 054-20224) and 1xPBS (pH 7.2) in a 1:3 ratio. For the positive control (PC), WBCs were purified from the blood of a healthy donor, resuspended in the NC buffer, diluted to 100 cells/µL (PDRP threshold per ISPD guidelines), aliquoted, and stored at -80°C until analysis.

For the leukocyte strip test, a thawed PC, an NC, and six thawed spent PDE (250 µL each) were arranged in a row. Eight urinary test strips containing leukocytes test pads (LotFancy, 11J-2136-D.1) were simultaneously dipped into samples for two seconds, then laid flat while a video was recorded to capture the color changes over 10 minutes. Signal intensities were analyzed by ImageJ (https://imagej.net/).

Results:

Figure 1A presents an example of a still image extracted from a video at the 5-minute mark. Sample 1F01 is a clinically diagnosed bacterial peritonitis case. Note that neither nitrite nor pH tests were performed.

Test strip results for freshly extracted and frozen-thawed WBCs at 100 cells/µL were compared. Both were from the same batch, with the frozen-thawed WBCs frozen at -80°C for an hour, while the fresh cells were kept at room temperature for the same duration. The results showed that the signal intensity from the frozen-thawed WBCs was consistently higher than that from the fresh WBCs (Figure 1B). For the fresh WBCs, the color change was visible to the naked eye as early as 2 minutes.

Among the 162 PDE, five were identified as bacterial peritonitis through clinical diagnosis or positive bacterial culture. All five PDE exhibited color intensities higher than the PC, yielding a test sensitivity of 100%. The remaining 157 PDE showed either no color change or intensities lower than the PC, resulting in a test specificity of 100%. Figure 1C summarizes the results alongside their WBC counts, focusing on samples with WBC > 30 cells/µl.

Conclusions:

We demonstrate that urinary leukocyte test strips are a rapid and effective screening tool for PDRP, with 100% sensitivity and 100% specificity. Future research with fresh bedside samples in larger patient cohorts is warranted to validate these results. If corroborated, urinary test strips could provide an effective and inexpensive point-of-care test (less than 10 U.S. cents per test) to detect elevated leucocyte counts in PDE. This method would be of particular interest in resource-constrained settings, such as low- and middle-income countries.

I have no potential conflict of interest to disclose.

I did not use generative AI and AI-assisted technologies in the writing process.