C-reactive protein (CRP) in dogs — and why cats get SAA instead

What it shows

CRP is an acute phase protein: during inflammation, signal molecules from inflamed tissue make the liver release it into the blood. In dogs it is one of the two major acute phase proteins, together with serum amyloid A. In a healthy dog CRP is low; with acute inflammation or injury it climbs quickly — significantly within hours, by 50 times or more, with a peak at about one to two days.

It also falls quickly once inflammation resolves, so repeated measurements show whether things are improving or relapsing. Unlike the white cell count, CRP is not moved by stress or excitement, and it is not affected by corticosteroids. That makes it useful when other signs of inflammation are missing.

Higher than reference — what it may be a sign of

• Systemic inflammation of any origin — CRP does not tell infection from non-infectious inflammation.
• Infections: bacterial pneumonia, pyometra, parvovirus, leptospirosis, vector-borne infections, sepsis.
• Immune-mediated disease: immune-mediated haemolytic anaemia, immune thrombocytopenia, immune-mediated polyarthritis, steroid-responsive meningitis-arteritis.
• Acute pancreatitis and some tumours.
• Recent surgery or trauma — surgery alone raises CRP within a day.

Some conditions usually leave CRP unchanged: osteoarthritis, cruciate ligament rupture, disc disease, idiopathic epilepsy, chronic bronchitis.

Lower than reference

A low CRP is the usual state of a healthy dog, and the sources describe no disease that it points to. A value that falls between two tests is read as inflammation settling; a rise again after it had fallen can be an early sign of relapse.

Look at together with

• White blood cells and neutrophils — the cell picture of inflammation; they can also change from stress, excitement or medicines, which do not move CRP.
• Serum amyloid A (SAA) — the other major acute phase protein in dogs, and the main one in cats.
• Pancreatic lipase — when pancreatitis is suspected; CRP adds how intense the inflammation is.
• The clinical picture — CRP shows that inflammation exists; where it is and why is found by examination and other tests.

Units and conversion

Labs report CRP in mg/L or mg/dL. One mg/dL equals 10 mg/L, so 3.0 mg/dL is 30 mg/L. The two units differ tenfold, which makes it easy to misread a number — always check which unit is printed. In the app each row keeps the unit from the form; the chart converts to one unit.

Reference range

The reference range is on your lab’s form. Higher values mean more intense inflammation. For its in-clinic canine test, IDEXX describes CRP above 3.0 mg/dL (30 mg/L) as clinically significant systemic inflammation. The trend matters more than one result: a falling CRP over repeated tests matches clinical improvement. Citrate tubes lower the value.

Cats and dogs

Sources

1. Cornell University Animal Health Diagnostic Center — C-Reactive Protein
2. eClinPath (Cornell University College of Veterinary Medicine) — Acute phase proteins
3. IDEXX — The IDEXX Catalyst CRP Test for in-house measurement of C-reactive protein (white paper)
4. IDEXX — Holy CRP: when and how to use C-reactive protein in sick dogs