**Background:** COVID-19, caused by SARS-CoV-2, has resulted in over 660 million cases and 6.7 million deaths worldwide as of January 2023. The disease presents with high clinical variability, and identifying prognostic factors for morbidity and mortality remains critical. Phase angle (PhA), derived from bioelectrical impedance analysis (BIA), is a cellular health biomarker that reflects fluid distribution between extracellular and intracellular compartments and cell membrane integrity. PhA has been associated with malnutrition, inflammation, and mortality in various clinical conditions, but its routine use in COVID-19 had not been established. This systematic review with meta-analysis aimed to establish the clinical value of PhA as a prognostic marker for adverse outcomes in hospitalized COVID-19 patients and to develop evidence-based recommendations using the GRADE methodology.
**Methods:** The review followed PRISMA guidelines and was registered on PROSPERO (CRD42023391044). A comprehensive literature search was conducted in MEDLINE/PubMed, Scopus, Embase, and Web of Science from database inception to January 2023. Search terms included combinations of "SARS-CoV2," "COVID," "COVID-19" with "bioelectrical impedance," "BIA," "bio-impedance," "phase angle," and "PhA." Inclusion criteria followed the PICO framework: COVID-19 patients (population), BIA assessment with PhA (intervention), altered vs normal PhA results (comparison), and outcomes including mortality, length of stay, disease severity, and complications (outcomes). Exclusion criteria included non-English/Spanish articles, non-peer-reviewed studies, reviews, case series, editorials, and studies in pregnant/lactating women or animal models. Four independent authors screened articles, and methodological quality was assessed using GRADE methodology. Meta-analysis was performed using Review Manager 5.3, with random-effects models applied when heterogeneity I² > 50%.
**Key Results:** From 483 initially identified studies, 8 studies met inclusion criteria (854 total patients). Six were prospective observational cohort studies, one was cross-sectional, and one was retrospective. Studies were conducted in European countries (Netherlands, Switzerland, Spain, Italy) and Mexico. Mean patient age ranged from 54 to 69 years, with male predominance (>60%) in all studies. The average PhA ranged from 4.4° to 5.6°, with lowest values in ICU patients. Significantly lower PhA values were found in patients with poor outcomes across all but two studies. For mortality, the highest hazard ratio was 3.912 (95% CI 1.322–11.572, p=0.014) for 90-day mortality, with a PhA cut-off of 3.95° (sensitivity 93.8%, specificity 66.7%). Another study found PhA <3.66° had HR 2.571 (95% CI 1.217–5.430, p=0.013) for 20-day mortality. The meta-analysis of 502 patients showed significantly increased mortality risk with lower PhA (RR 2.44, 95% CI 1.20–4.99, p=0.01; I²=79%). For complications (316 patients), lower PhA was associated with increased risk (OR 3.47, 95% CI 1.16–10.37, p=0.03; I²=82%). PhA was not a significant predictor of disease severity (444 patients; RR 1.59, 95% CI 0.94–2.69, p=0.08). Post-extubation dysphagia showed a strong association with PhA <4.8° (OR 12.2, 95% CI 4.3–34.1, p<0.05). GRADE assessment rated evidence quality as moderate for mortality prediction and low-to-moderate for complications.
**Clinical Implications:** This review provides evidence that low PhA is a valid prognostic indicator for mortality and complications in hospitalized COVID-19 patients. The GRADE-based recommendations support strong recommendations for using PhA to predict mortality (moderate quality evidence) and complications (low-to-moderate quality evidence), with weaker recommendations for predicting length of stay and disease severity. PhA assessment is fast, non-invasive, portable, and reproducible, making it practical for clinical use. The findings suggest that low PhA reflects both overhydration (from inflammation) and reduced cell mass (from malnutrition/sarcopenia), providing integrated prognostic information. However, heterogeneity across studies in BIA devices, measurement protocols, and PhA cut-off values limits direct comparability. Future research should focus on establishing standardized PhA thresholds and incorporating standardized phase angle (adjusted for age and sex) to improve clinical utility. Despite these limitations, PhA represents a valuable tool for early risk stratification and individualized therapeutic management of hospitalized COVID-19 patients.