Serum amyloid A (SAA) in cats and dogs

What it shows

When tissue is inflamed, signal molecules tell the liver to release acute phase proteins into the blood. SAA is one of them, and it is a major one: in acute inflammation it can rise 100 to 1000 times within 24–48 hours. In healthy animals it is very low.

SAA also drops quickly after inflammation resolves. That makes it useful for following one animal over time: a falling value supports improvement, a value that stays high suggests the inflammation is still active. In dogs, unlike in people, corticosteroids do not raise SAA.

Higher than reference — what it may be a sign of

• Systemic inflammation — infectious or not: in dogs SAA rises with both septic and non-septic inflammation, so a high value does not show the cause or the organ.
• Severe inflammation — the stronger the inflammatory reaction, the higher SAA tends to climb; the rise can be hundreds of times above the usual level.
• Inflammation that lasts for a long time — persistently high SAA can lead to amyloidosis, where misfolded SAA is deposited in organs.

Because SAA is not specific, the vet looks for the source of inflammation with examination and other tests.

Lower than reference

A very low or undetectable SAA is the usual state of a healthy animal; the sources describe no disease that a low value points to. A value that falls between tests is read as inflammation resolving. One caveat, shown in horse samples: storage can lower a mildly raised value into the range, so a delayed sample can understate inflammation.

Look at together with

• C-reactive protein (CRP) — in dogs the second major acute phase protein; in cats CRP is not among the main ones, so SAA takes its place.
• White blood cells and neutrophils — the cell picture of inflammation.
• Iron — serum iron falls in inflammation; in experimental inflammation it dropped even before SAA rose.
• Globulins — SAA is present in small amounts, so even a marked rise may not show on protein electrophoresis.

Units and conversion

Labs report SAA in µg/mL or mg/L. These are the same quantity: 1 µg/mL equals 1 mg/L, so no conversion is needed. Point-of-care analyzers do not always agree with laboratory methods, especially at high values, so it is better to follow the trend on the same method.

Reference range

The reference range is on your lab’s form. SAA is read in two ways: whether it is raised at all, and how it changes between repeated tests. Because it rises and falls quickly, a recheck can show whether inflammation is settling. A raised value says nothing about the cause on its own. Samples kept for more than a day are best frozen, and labs prefer serum or heparin plasma.

Cats and dogs

Sources

1. eClinPath (Cornell University College of Veterinary Medicine) — Serum Amyloid A
2. eClinPath (Cornell University College of Veterinary Medicine) — Acute phase proteins
3. Tizard IR. Amyloidosis in Animals. Merck Veterinary Manual
4. Cornell University Animal Health Diagnostic Center — Now Offering Serum Amyloid A (SAA) Testing