|Values are valid only on day of printing.|
All but 2% to 5% of serum fatty acids are esterified. The "nonesterified" or "free" fatty acids are protein-bound. The amount of free fatty acids in the serum rises after a fatty meal, but tends to fall after ordinary meals. Levels are elevated in obesity.
Lipoactive hormones such as epinephrine, norepinephrine, glucagon, thyrotropin, and adrenocorticotropin release free fatty acids. Tumors producing such hormones cause release of excessive quantities of free fatty acids. Serum free fatty acids are also increased in patients with uncontrolled type 2 diabetes mellitus and are an indicator of insulin resistance. Free fatty acids are associated with increased reactive oxygen species (ROS), probably mediated by free fatty acid activation of NADPH oxidase. The link between increased ROS and decreased nitric oxide production is a contributor to endothelial dysfunction.
Evaluation of metabolic status of persons with endocrinopathies
Detection of pheochromocytoma and of glucagon-, thyrotropin-, and adrenocorticotropin-secreting tumors
Monitoring of control of diabetes mellitus (serum-free glycerol is a very useful companion test in assessing diabetes and may be ordered by special request from Mayo Medical Laboratories). The correlation with insulin resistance and downstream cardiovascular risk may be a useful treatment aid in some patients.
Abnormally high levels of free fatty acids are associated with uncontrolled diabetes mellitus and with conditions that involve excessive release of a lipoactive hormone such as epinephrine, norepinephrine, glucagon, thyrotropin, and adrenocorticotropin.
Patient should fast for 12 to 14 hours; however, in prolonged fasting or starvation, free fatty acid levels rise as much as 3-fold.
Patient should abstain from alcohol for at least 24 hours.
In order to eliminate the generation of free fatty acids from triglycerides by serum lipases (causing erroneous elevations), serum should be frozen soon after it is drawn and shipped frozen.
> or =16 years: 0.00-0.72 mmol/L
Reference values have not been established for patients who are <16 years of age.
1. Dole VP: A relation between non-esterified fatty acids in plasma and the metabolism of glucose. J Clin Invest 1956;35:150-154
2. Imrie H, Abbas A, Kearney M: Insulin resistance, lipotoxicity and endothelial dysfunction. Biochim Biophys Acta, 2010 Mar;1801 (3):320-326