Coefficient of Fat Absorption to Measure the Efficacy of Pancreatic Enzyme Replacement Therapy in People With Cystic Fibrosis: Gold Standard or Coal Standard?

We sought data on the validity, reliability, responsiveness, and feasibility of the coefficient of fat absorption (CFA) as a measure of pancreatic enzyme replacement therapy (PERT) efficacy in people with cystic fibrosis (pwCF) and reviewed the literature for alternative measures. METHODS: We searched PubMed for the Medical Subject Heading cystic fibrosis and the key words cystic fibrosis, fat absorption, CFA, and fecal fat imbalance; historical articles; and citations in bibliographies. RESULTS: The lower the CFA, the greater its variability; thus, it is less variable in healthy individuals who have higher CFA than pwCF. In addition, the test-retest values for CFA are more variable in pwCF than the general population. There is no correlation between CFA and body mass index or PERT dose but CFA is related to gastrointestinal signs and symptoms. Research-quality CFA studies are expensive, time consuming, and odious to pwCF and research staff. Sparse stool tests, breath tests, and blood tests of fat absorption have been studied as potential alternatives to CFA to measure PERT efficacy. CONCLUSIONS: Based on the evidence, we conclude that CFA as a measure of the efficacy of PERT is more of a “coal standard” than a gold standard; developing suitable alternatives should be a priority.