Free fatty acids are formed by lipoprotein and triglyceride breakdown. The amount of free fatty acids and triglycerides present in blood comes from dietary sources or fat deposits or is synthesized by the body. Carbohydrates can be converted to fatty acids and then stored in fat cells as triglycerides. Fatty acid and carbohydrate metabolism is altered in the fat breakdown process (e.g., when fasting). Unusually high levels are associated with untreated diabetes.

Specific fatty acid measurement can be useful for monitoring nutritional status in the presence of malabsorption, starvation, and long-term parenteral nutrition. It is also valuable for the differential diagnosis of polyneuropathy when Refsum disease is suspected. With this disease, the enzyme that degrades phytanic acid is lacking. Free fatty acids are also useful in detecting pheochromocytoma and glucagon thyrotropin and adrenocorticotropin-secreting tumors.

Adults: 8–25 mg/dL or 0.28–0.89 mmol/L

Children (or adults who are obese): <31 mg/dL or <1.0 mmol/L

Fatty Acid Profile:

• Linoleate: >25% or >0.25 of total fatty acids

• Arachidate: 0%–6% or 0.00–0.06

• Oleic: 26%–35% or 0.26–0.35

• Linoleic: 8%–16% or 0.08–0.16

• Steric: 10%–14% or 0.10–0.14

Phytanic Acid:

• Normal: 0.3% or 0.003

• Borderline: 0.3%–0.5% or 0.003–0.005

1. Obtain a 5-mL blood sample and place on ice. Serum or EDTA plasma may be used.

2. Fasting is required.

3. The blood serum should be separated from blood cells within 45 minutes of collection and should be placed on ice. Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.

1. Increased free fatty acid values are associated with the following conditions:

   1. Poorly controlled diabetes

   2. Pheochromocytoma

   3. Hyperthyroidism

   4. Huntington disease (neurodegenerative genetic disorder)

   5. von Gierke disease (glycogen storage disease due to deficiency of glucose-6-phosphatase)

   6. Alcoholism

   7. Acute MI

   8. Reye syndrome

2. Increased phytanic acid occurs in the following conditions:

   1. Refsum disease (autosomal recessive neurologic disease); if >50%, repeat the test to confirm

   2. β-Lipoproteinemia

3. Decreased fatty acids are found in:

   1. Cystic fibrosis

   2. Malabsorption (acrodermatitis enteropathica)

   3. Zinc deficiency (linoleate and arachidate low)

Pretest Patient Care

1. Explain test purpose and blood-drawing procedure. Fasting is required, but water may be taken.

2. Do not test patients receiving heparin therapy. For free fatty acids, no alcohol may be taken within 24 hours.

3. Discontinue strenuous exercise before the test. Encourage relaxation.

4. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Values are elevated by strenuous exercise, anxiety, hypothermia, certain drugs (see Appendix E), and long-term fasting.

2. Values are decreased by long-term IV or parenteral nutrition therapy and certain drugs (see Appendix E).

3. Prolonged fasting or starvation affects levels (rise as much as three times normal).