# Detection of Latent Tuberculosis in Chronic Kidney Disease (CKD) Patients on Dialysis Using the Cy-TB Test: A Hospital-Based Cross-Sectional Study

## TL;DR

This study finds that the Cy-TB test agrees with existing methods for detecting latent TB in dialysis patients, with higher detection rates in those on dialysis for less than six months.

## Contribution

The study is the first to evaluate the Cy-TB test for latent TB in CKD patients on dialysis and identifies an early dialysis phase as a potential screening window.

## Key findings

- The overall prevalence of latent TB in dialysis patients was 4.2%, much lower than previously reported.
- Dialysis duration under six months was the strongest predictor of latent TB positivity.
- The Cy-TB test showed perfect agreement with IGRA in the few confirmed cases, though this result is based on a small sample.

## Abstract

Background

Latent tuberculosis infection (LTBI) represents a major health burden in chronic kidney disease (CKD) patients on hemodialysis due to severe immunosuppression. Current diagnostic methods have limitations in this population. The Cy-TB test is a novel immunological assay for detecting TB infection, but its performance in patients with CKD undergoing dialysis is unknown.

Objectives

The primary objective was to estimate the prevalence of LTBI in CKD patients on maintenance hemodialysis using the Cy‑TB skin test and to describe its agreement with interferon‑gamma release assay (IGRA) among Cy‑TB-positive cases. Secondary objectives were to identify clinical and demographic factors associated with Cy‑TB positivity and to explore whether the early dialysis phase (<6 months) represents a higher‑yield window for LTBI screening.

Methods

This hospital-based cross-sectional study enrolled 95 consecutive CKD patients on maintenance hemodialysis. All participants underwent Cy-TB testing with induration measurement at 48-72 hours; positive cases were confirmed by IGRA reference testing. Clinical and demographic data were collected through structured assessment. Diagnostic accuracy metrics, odds ratios (ORs) with 95% confidence intervals (CIs), and effect sizes (Cohen's d) were calculated using logistic regression and univariable statistical analysis.

Results

The overall prevalence of LTBI was 4.2% (4/95; 95% CI: 1.2%-10.3%), substantially lower than the 15-25% range reported in prior international dialysis cohorts. Dialysis duration <6 months emerged as the strongest independent predictor of Cy-TB positivity (p=0.001; OR=13.5; 95% CI: 2.5-72.8), with 75% of positive cases (3/4) occurring within this early dialysis phase and a 17.6% prevalence compared to 1.3% in chronic dialysis patients (≥6 months duration). Prior history of tuberculosis was significantly associated with increased positivity risk (p=0.048; OR=25.2; 95% CI: 1.4-442.8). Urban residence (p=0.073), presence of comorbidities (p=0.072), and elevated fever (p=0.099) showed marginal associations. Age, gender, body mass index, smoking status, alcohol consumption, TB contact history, and respiratory symptoms demonstrated no significant associations. Among the four LTBI‑positive cases identified, the Cy‑TB test showed perfect agreement with IGRA; however, this finding is based on a very small number of events and should be interpreted cautiously.

Conclusions

In this single-center cross-sectional cohort, the Cy-TB test showed excellent agreement with IGRA for LTBI detection in CKD-dialysis patients, based on a small number of LTBI-positive cases. The observed association between the early dialysis phase (<6 months) and higher LTBI detection suggests this period as a potential priority window for LTBI screening. These findings are exploratory and hypothesis-generating and require confirmation in larger, comparative, and longitudinal studies before any changes to screening strategies are recommended.