Glossary
Acute phase protein.
Direct answer
An acute phase protein is a blood protein whose concentration changes markedly during inflammation, injury or infection. The liver increases, and in some cases decreases, production of these proteins in response to cytokine signals. They are measured to make an inflammatory reaction visible and to follow its course over time.
Acute phase proteins are graded by speed and size of response. A major protein multiplies within hours; a moderate protein rises more slowly and less steeply. Direction matters too: albumin falls during inflammation, so a low value here need not mean deficiency. None of these proteins names a cause; all of them report activity.
The ranking is species dependent, which is exactly where comparison pays off. In the horse, serum amyloid A is the major protein and fibrinogen the slower, moderate one. In humans and dogs, C-reactive protein leads instead. Taking the marker of one species and applying it to another means measuring beside the event.
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