Objective: To evaluate the perception of disease severity in patients with cystic fibrosis (CF), investigating its relationship with clinical score, radiographic score, respiratory function tests, adherence to treatment and perception of self-care practices. Methods: Prospective, cross-sectional study involving CF patients treated in a program for adults with CF. The perception of disease severity, adherence to treatment and reported self-care practices were evaluated by means of questionnaires. Clinical data, Shwachman-Kulczycki clinical score, Brasfield radiographic score and spirometry were obtained for all of the patients. Results: Of the 38 patients studied, 3 (7.9%) patients rated their perception of health status as well below average; 5 (13.2%), as below average; 15 (39.5%), as average; 10 (26.3%), as above average; and 5 (13.2%), as well above average. The perception of disease severity correlated significantly with clinical score (r = 0.43, p = 0.007), FVC (r = 0.34, p = 0.034), FEV1 (r = 0.38, p = 0.019) and self-care practices (r = 0.33, p = 0.044), but not with degree of adherence (r = -0.03, p = 0.842) and radiographic score (r = 0.33, p = 0.51). Conclusions: The perception of disease severity correlated with objective measurements of disease severity (clinical score and respiratory function tests) and with reported self-care practices, but not with adherence to treatment.

Keywords: Severity of illness index; Cystic fibrosis; Patient compliance; Respiratory function tests.