An apparatus may include a sensing circuit configured to generate a sensed physiological signal representative of thoracic impedance of a subject and a controller circuit. The a controller circuit is electrically coupled to the sensing circuit and includes a measurement circuit that determines a measure of absolute thoracic impedance using the sensed physiological signal, and a risk circuit that quantifies a risk of worsening heart failure (WHF) for the subject using a comparison of the determined measure of absolute thoracic impedance to a specified threshold value of absolute thoracic impedance, and generate an indication of risk of WHF of the subject according to the quantifying of the risk.
