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 (PaO(2)) and carbon dioxide (PaCO(2)) 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 (FEV(1)) recorded at the start of the study was 1.8 (1.0) l (52 (26)% predicted FEV(1)), 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). FEV(1), % predicted FEV(1), PaO(2), % ideal weight (all p<0.0001), and PaCO(2) (p=0.04) predicted survival. In multivariate analysis, % predicted FEV(1) (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 < or =85% ideal weight (survival 53%, 95% CI 45 to 62), p<0.0001. Percentage predicted FEV(1) (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.