NEFA (free fatty acids) in cats and dogs

NEFA — non-esterified, or free, fatty acids — are the fatty acids released when the body breaks down its fat stores for energy. The level rises with fasting and negative energy balance, with stress and excitement, and in small animals mainly with diabetes mellitus. The test is used chiefly in dairy cattle and other farm animals; in dogs and cats it is ordered rarely.

SectionBiochemistry
SampleBlood (serum or EDTA plasma, not heparin), ideally taken before feeding and with little stress; serum separated promptly and kept cool
Unitsmmol/L
On formsNEFA, FFA

What it shows

Fatty acids are the main building blocks of triglycerides. In a fed animal the NEFA in blood come mostly from fat in the food. During fasting or negative energy balance — when the body uses more energy than it takes in — they come mainly from breaking down body fat. This is done by hormone-sensitive lipase in fat tissue. Adrenaline-like hormones, glucagon, growth hormone, thyroxine, ACTH and corticosteroids switch it on; insulin switches it off.

Released NEFA travel to the liver, free or bound to albumin. The liver burns them for energy, packs them back into triglyceride-rich VLDL particles or turns them into ketones. So NEFA show how hard the body is mobilising fat, while ketones such as β-hydroxybutyrate show what the liver makes of that fat.

Higher than reference — what it may be a sign of

  • Fasting and negative energy balance — not eating, or eating too little for the body’s needs, mobilises fat.
  • Stress, excitement and exercise — they release adrenaline-like hormones or ACTH, which speed up fat breakdown; a struggle during blood sampling can raise the value.
  • Diabetes mellitus — in small animals the main described cause: without enough insulin, or when the body resists it, the brake on fat breakdown is lost.
  • Sample handling — NEFA rise during storage, especially in heparin tubes, and increase after 24–48 hours at room temperature.

Lower than reference

NEFA are lower soon after a meal, because feeding suppresses fat breakdown. Values below the reference limit are not considered clinically relevant.

Look at together with

  • β-hydroxybutyrate (BHB) — the main ketone; NEFA show fat release, BHB shows ketone production from it.
  • Glucose, fructosamine and insulin — to judge whether diabetes or insulin resistance stands behind a high NEFA.
  • Triglycerides and cholesterol — fat breakdown increases the liver’s output of triglyceride-rich particles; a high NEFA to cholesterol ratio has been studied as a marker of fatty liver in cattle.

Units and conversion

NEFA are reported in mmol/L — millimoles per litre. Some laboratories, especially in farm-animal work, print the result in milliequivalents per litre; for NEFA the two are equal one to one, so the number does not change. In the app the row keeps the number and unit printed on the form.

Reference range

The reference range is on your lab’s form. Teaching sources give detailed cut-offs for dairy cows around calving and for camelids, but these are herd risk thresholds for farm animals and do not apply to dogs and cats. For a pet, the value is read against the interval the laboratory gives for the species. Because stress, a recent meal and storage all shift NEFA, a result is easiest to interpret when blood is taken before feeding, calmly, and the serum is separated and cooled quickly.

Cats and dogs

Cats

In cats, fat mobilised from the body faster than the liver can use or export it builds up in liver cells — this is feline hepatic lipidosis, which develops in overweight cats that stop eating. Its diagnosis rests on blood tests, ultrasound and cytology of a liver aspirate, not on NEFA. In a study of cats with different body condition scores, NEFA showed only a tendency to rise with weight, and the hormone adiponectin changed earlier than NEFA.

Dogs

In dogs, as in other small animals, a raised NEFA is mainly linked to diabetes mellitus, when insulin no longer restrains fat breakdown. Stress, excitement and exercise around sampling can raise it as well, so a calm sample taken before a meal is easier to read. NEFA are not part of a routine canine panel; a vet orders them for a specific question about energy metabolism.

In the app

Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.

Open the app

Sources

  1. eClinPath (Cornell University College of Veterinary Medicine) — NEFA (non-esterified fatty acids).
  2. eClinPath (Cornell University College of Veterinary Medicine) — Lipid overview.
  3. Center SA. Feline Hepatic Lipidosis. Merck Veterinary Manual, professional version, full review August 2023 (last updated June 2025).
  4. Okada Y, Kobayashi M, Sawamura M, Arai T. Comparison of Visceral Fat Accumulation and Metabolome Markers among Cats of Varying BCS and Novel Classification of Feline Obesity and Metabolic Syndrome. Frontiers in Veterinary Science, 2017;4:17.

This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.