Relationship between low phase angle and impaired healing of diabetic foot ulcer: a retrospective cohort study

Phase angle (PhA), an objective parameter derived from bioelectrical impedance analysis that reflects cellular mass and membrane integrity, has been recognized as a significant biomarker for evaluating malnutrition and systemic inflammation. The present study was designed to explore the independent prognostic significance of systemic PhA for healing in individuals with diabetic foot ulcer (DFU). This retrospective cohort study encompassed 182 hospitalized patients with DFU (mean age: 66.5 years) between October 2019 and June 2021. The relationship between PhA and ulcer healing was examined through multivariate modified Poisson regression analysis. Restricted cubic splines and subgroup analyses were employed to investigate potential non-linear associations and effect modifiers. At the 6-month follow-up, 93 participants (51.1%) exhibited persistent ulceration. Relative to the healed group, the unhealed cohort demonstrated markedly lower PhA values (P < 0.001) and elevated hydration indices (P < 0.001). Following adjustment for all potential confounders, both PhA (relative risk [RR] = 0.80, 95% confidence intervals [CI]: 0.64–0.99) and hydration parameters (RR = 1.34, 95% CI: 1.04–1.71) were independently associated with impaired DFU healing. A PhA threshold of 3.8° yielded optimal diagnostic efficacy for predicting non-healing, with a sensitivity of 66.7% and specificity of 65.2%, surpassing conventional nutritional indicators such as hemoglobin and albumin. Participants with PhA ≤ 3.8° experienced a 37% higher risk of non-healing ulcers compared to those with PhA > 3.8° (RR = 1.37, 95% CI: 1.01–1.88), with the association being particularly prominent among female patients (RR = 5.40, 95% CI: 1.78–16.65) and individuals exhibiting estimated glomerular filtration rate (eGFR) ≥ 60 ml/min/1.73 m² (RR = 2.01, 95% CI: 1.25–3.23). PhA, as quantified by bioelectrical impedance analysis, represents a promising candidate biomarker for exploratory prognostic evaluation in DFU patients, exhibiting enhanced predictive capacity particularly in females and those with preserved or mildly compromised renal function. These exploratory findings suggest that PhA monitoring may have the potential to identify individuals at elevated risk for poor ulcer healing, with clinical implementation pending external prospective validation.