Expansion
CRP rises and falls fast; ESR is slow and influenced by many factors
Expansion
| CRP | ESR | |
|---|---|---|
| What it measures | An acute phase protein made by the liver | The rate red cells settle, driven by fibrinogen and immunoglobulins |
| Rise | 6 to 8 hours, peaks at 48 | 24 to 48 hours |
| Fall | Rapid, half life about 19 hours | Slow, over weeks |
| Best for | Acute infection, monitoring response | Chronic inflammation, giant cell arteritis, polymyalgia, myeloma |
Factors raising the ESR independently of inflammation: age (a rough upper limit is age divided by 2 in men, and age plus 10 divided by 2 in women), female sex, anaemia, pregnancy, obesity, renal failure, and paraproteins.
Factors lowering the ESR: polycythaemia, sickle cell disease, spherocytosis, very high white cell counts, hypofibrinogenaemia, and heart failure. These can mask inflammation.
Where the ESR still earns its place
- Giant cell arteritis and polymyalgia rheumatica, where it remains part of the diagnostic criteria
- Myeloma, where a very high ESR with a normal CRP is characteristic
- Monitoring chronic disease activity in rheumatoid arthritis and lupus, where CRP may be normal despite active disease
A normal CRP does not exclude serious disease. It is often normal in systemic lupus erythematosus (unless there is serositis or infection), in some viral infections, and in liver failure, where the liver cannot mount the response.