BACKGROUND Cystic fibrosis (CF) is the most common life threatening autosomal recessive disorder in the white population. Wasting has long been recognised as a poor prognostic marker in CF. Whether it predicts survival independently of lung function and arterial blood gas tensions has not previously been reported.

RESULTS Forced expiratory volume in one second (FEV₁) recorded at the start of the study was 1.8 (1.0) l (52 (26)% predicted FEV₁), Pao ₂ 9.8 (1.9) kPa, Paco ₂ 5.0 (0.9) kPa, and % ideal weight 92 (18)%. During the follow up period (45 (27) months) 137 patients died (5 year survival 72%, 95% CI 67 to 73). FEV₁, % predicted FEV₁, Pao ₂, % ideal weight (all p<0.0001), and Paco ₂ (p=0.04) predicted survival. In multivariate analysis, % predicted FEV₁ (p<0.0001), % ideal weight (p=0.004), and Paco ₂ (p=0.02) were independent predictors of outcome. Patients with >85% ideal body weight had a better prognosis at 5 years (cumulative survival 84%, 95% CI 79 to 89) than those with ⩽85% ideal weight (survival 53%, 95% CI 45 to 62), p<0.0001. Percentage predicted FEV₁ (area under curve 0.83; 95% CI 0.78 to 0.87) and % ideal weight (area under curve 0.74; 95% CI 0.68 to 0.79) were accurate predictors of survival at 5 years follow up (receiver-operating characteristic analysis).

CONCLUSIONS Body wasting is a significant predictor of survival in patients with CF independent of lung function, arterial blood oxygen and carbon dioxide tensions.