A novel method of diagnosing cystic fibrosis in a human subject is provided. The method includes the steps of: i) determining in a biological sample from the subject the level of one or more metabolic biomarkers； ii) comparing the level of the biomarker to a control level and determining the difference between the biomarker level and the control level； and iii) determining that the subject has cystic fibrosis or a related disorder when the difference in the level of the biomarker in the sample is statistically different from the control level.
