Wasting as an independent predictor of mortality in patients with cystic fibrosis

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. Methods - 584 patients with CF (261 women) of mean (SD) age 21 (7) years were studied between 1985 and 1996, all of whom were being followed up in a tertiary referral centre. Lung function tests, body weight, arterial blood oxygen (Pao₂) and carbon dioxide (Paco₂) tensions were measured. The weight was calculated as a percentage of the ideal body weight for age, height, and sex. Results - Forced expiratory volume in one second (FEV₁) recorded at the start of the study was 1.8 (1.0)1 (52 (26)% predicted FEV₁), Pao₂ 9.8 (1.9) kPa, Paco₂ 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, Pao₂, % ideal weight (all p<0.0001), and Paco₂ (p=0.04) predicted survival. In multivariate analysis, % predicted FEV₁ (p<0.0001), % ideal weight (p=0.004), and Paco₂ (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.