Direct transesterification of plasma fatty acids for the diagnosis of essential fatty acid deficiency in cystic fibrosis.

This study was aimed at redefining criteria for essential fatty acid (EFA) deficiency with the use of the direct transesterification procedure (1986. J. Lipid Res. 27: 114-120) and at determining whether a simple assay of total fatty acids (FA) is as predictive of EFA deficiency as the FA pattern from plasma, red cell, and platelet phospholipids. Fasting blood samples were taken from 163 cystic fibrosis (CF) patients who were encouraged to consume 35-40% of their calories as fat. Their mean (+/- SD) age was 9.6 +/- 4.8 yr. The control group consisted of 44 unaffected siblings aged 13.1 +/- 3.1 yr. The 20:3(n-9)/20:4(n-6) ratio in 77 (47%) CF children was more than 2 SD above the values (mean +/- SD) of 0.021 +/- 0.007 obtained in the 44 controls. Groups of EFA-sufficient (n = 10) and EFA-deficient (n = 7) subjects were selected for further studies. The plasma total FA 20:3(n-9)/20:4(n-6) ratios of 0.029 +/- 0.003 in EFA-sufficient and of 0.216 +/- 0.103 in EFA-deficient was as good a discriminant as FA in phospholipids from plasma, red cell PC, and platelets. Among the 21 individual fatty acids, 20:3(n-9), which was also found in controls, and 16:1(n-7) (palmitoleic) proved to be the most sensitive indices of EFA deficiency. They are equally reliable in plasma, red cells, and platelets, but the inverse linear relationship (r = -0.91) between the n-7 family and 18:2(n-6) proved to be more closely associated with EFA deficiency than the one (r = 0.66) between 20:3(n-9) and 20:4(n-6).(ABSTRACT TRUNCATED AT 250 WORDS)