The Expanding Role of Carbohydrate Antigen 125 in Heart Failure: From Tumour Marker to a Cornerstone of Heart Failure Management. An Updated Narrative Review.

Congestion is central to heart failure (HF) but remains difficult to quantify. Carbohydrate antigen 125 (CA125), also known as mucin 16, released by mesothelial cells, captures two pathways relevant to HF: fluid overload and inflammation. This narrative review summarises biological mechanisms and clinical applications. Across acute and chronic settings, CA125 tracks systemic and right-sided congestion, complements natriuretic peptides and shows lower dependence on renal function. Higher levels identify patients at risk for death and readmission; in ambulatory HF with reduced ejection fraction it predicts events, while in HF with preserved ejection fraction its signal is strongest in congestion-dominant phenotypes. Serial testing mirrors decongestion and clinical course; CA125-guided care has reduced rehospitalisations and improved renal function measures in selected populations. Advantages, wide availability, standardisation and low cost, support use in practice. Key gaps include phenotype-specific threshold, sampling interval and integration into actionable algorithms. Overall, CA125 has moved from tumour marker to practical tool that refines congestion assessment, improves risk stratification and informs individualised therapy in contemporary HF care.