Concentration of Some Fatty Acids in Human Blood, Blood Plasma or Blood Serum

There are two major sources of fatty acids in blood, non-esterified fatty acids (NEFA) which are also referred to as free fatty acids (FFA) and fatty acids present in acyl linkage such triacyl glycerides. It is thought that NEFA in blood are derived from the hydrolysis of stored triacyl glycerols¹ but there can be some contribution from diet.^2,3 So, most of the studies are performed in fasting subjects. It has been reported that there is a small increase in free fatty acids in human serum following fasting.^4,5 Free fatty acids in blood are proposed as biomarkers.^6,7 Plasma free fatty acids are considered to be a major source of energy⁸ and have physiological function.⁹ Short-chain fatty acids (C2,C4,C6) are derived from carbohydrates by intestinal microbiota.¹⁰ There are three steps in the process of determining the concentration of free fatty acids and total fatty acids in blood. First, blood is obtained by venipuncture in the form of whole blood, plasma, or serum. Blood and plasma both require the use of an anticoagulant such as EDTA, citrate, or heparin, whereas serum is obtained from the coagulation of blood. The choice of anticoagulant does not seem to make a difference¹¹ although studies are limited. There are differences between serum and plasma.¹² The processing of blood samples is more critical for oxygenated polyunsaturated fatty acids (PUFA) such as eicosanoids, and the levels of these lipid mediators are higher in serum than in plasma.^13,14 There are also gender differences^14,15 and age differences¹⁵ in various lipids including lysophosphatidyl choline, diacyl glycerol, diHETrE (5,6-dihydroxyeicosatrienoic acid), and 8-HETE (8-hydroxyeicosatetraenoic acid).