Fat Malabsorption in Cystic Fibrosis: Comparison of Quantitative Fat Assay and a Novel Assay Using Fecal Lauric/Behenic Acid

Objectives: The “gold standard” for the diagnosis of fat malabsorption, the 72 hour fatbalance study, requires a three day collection to generate a coefficient of fat absorption (CFA). We hypothesized that, a new test using behenic acid (behenate test) as a nonabsorbable lipid marker may provide a facile means to assess fat absorption. The study proposed to answer two questions: 1) whether the “behenate test” correlated with the “gold standard” and 2) whether the CFA improved when taking pancreatic enzymes during meals instead of prior to them.

Methods: The study compared the “behenate test” with the gold standard in 15 cystic fibrosis patients during three arms which require 3-4 day hospitalizations: one taking pancreatic enzymes prior to meals, one taking pancreatic enzymes during meals, and one off of pancreatic enzymes.

Results: The mean CFA was 78.3% when pancreatic enzymes were taken during meals and 80.4% when pancreatic enzymes were taken prior to meals. Correlation between the CFA and the “behenate test” for collections during all 3 arms was r² = 0.219 (p= 0.001). Conclusion: 1) Timing of ingestion of pancreatic enzymes does not significantly alter the CFA. 2) Although the CFA correlates with the “behenate test”, the correlation is not robust enough to justify its replacement of the “gold standard.” It is unclear whether the poor correlation between tests relates to intermeal variability in fat excretion,or other factors; however the “behenate test” may be suitable as a screening test for detection of fat malabsorption.