Far-Infrared Irradiation Improves 12-Month ABI in Hemodialysis Patients: A Single-Center Study

In hemodialysis (HD) patients, peripheral arterial disease (PAD) and lower-limb circulatory impairment worsen survival and quality of life, while options are limited and surgical outcomes are poorer than in the general population. Far-infrared (FIR) irradiation is a bedside-feasible adjunct during HD sessions and has been suggested to improve endothelial function and microcirculation; however, its impact on the ankle–brachial index (ABI) over an annual timescale is unclear. We aimed to estimate the effect of FIR on ABI at 12 months and on the annual change in ABI (ΔABI/year) after adjustment for confounding.

Single-center retrospective cohort (July 2023–June 2025) of adult maintenance HD patients with baseline and 12-month ABI. We excluded limbs with major amputation, acute limb ischemia, or missing key covariates. The irradiation group received 30-minute FIR once per HD session for 1 year (adherence ≥80%); controls had no FIR during the target period or prior year. FIR followed the manufacturer’s manual with the emitter ~20 cm from the limb; nursing checks ensured correct placement and uninterrupted delivery. The limb was the unit of analysis; patient-level clustering was addressed. Primary outcomes were ABI at 12 months and ΔABI/year; secondary outcomes were ABI <0.90 and “Responder” (Δ ≥0.10). Main analysis: overlap weighting (OW) with doubly robust (DR) adjustment. Sensitivity: Inverse Probability of Treatment Weighting (IPTW)+DR, propensity score matching (PSM)+DR, mixed-effects (patient random intercept), and a patient-clustered nonparametric bootstrap (500 resamples). Balance used |SMD| ≤0.10. Prespecified covariates: age, sex, diabetes, smoking, systolic blood pressure, baseline ABI, log dialysis vintage, prior endovascular/surgical procedures, and concomitant medications. Approved by the institutional ethics committee (No. 4724); conducted per the Declaration of Helsinki with consent waived via public opt-out.

The analysis included 26 patients (51 limbs) in the irradiation group and 102 patients (199 limbs) in the non-irradiation group. In the main analysis (OW+DR), ABI at 12 months was higher in the FIR group (difference +0.060, 95% CI +0.019 to +0.100), and ΔABI/year was also improved (difference +0.056, 95% CI +0.021 to +0.090). Clustered bootstrap estimate: +0.051 (95% CI −0.006–0.098; P(effect<0)=0.034). Clinically, this corresponded to a 6.03% absolute reduction in ABI <0.90 (NNT 16.6) and an 11.67% absolute increase in Responders (NNT 8.6). Under the final condition, max|SMD| ≤0.10 was achieved; IPTW, PSM+DR, and mixed-effects analyses showed similar trends. No device-related events (low-temperature burns, erythema, discomfort-related discontinuation) occurred.

FIR administered during HD was associated with small-to-moderate improvements in ABI at 12 months and ΔABI/year. An effect of +0.05 to +0.06 may help patients near the ABI 0.90 threshold move into a lower-risk range, suggesting potential utility as a pragmatic adjunct to standard PAD care in HD. While residual confounding in this single-center observational study cannot be excluded, the direction of effect was consistent across multiple approaches. Prospective multicenter studies should evaluate durability, patient-centered outcomes (leg symptoms, walking distance), and cost-effectiveness.