Health Library / Blood tests
CRP and ESR: what inflammatory markers can and cannot tell you
· 5 min read
CRP and ESR appear on a great many requests, and both do the same broad job: they indicate that inflammation is happening somewhere in the body. Neither tells you where, and neither tells you why.
Understanding that limitation is what stops a raised marker turning into an open-ended and expensive search.
How the two differ
CRP is a protein the liver makes in response to inflammation. It rises quickly — within hours — and falls quickly once the cause resolves, which makes it good for tracking something in real time, such as whether an infection is responding to treatment.
ESR measures how fast red cells settle in a tube, which is influenced by proteins that change in inflammation. It rises and falls slowly, over days to weeks, and is affected by things that have nothing to do with inflammation at all — anaemia, pregnancy, age, and being female all raise it.
Because of that, a mildly raised ESR on its own is often not worth chasing, whereas a markedly raised one is meaningful. CRP is generally the more specific of the two.
CRP and hs-CRP are not the same request
This causes real confusion. Standard CRP is used to detect and follow significant inflammation — infection, inflammatory disease, post-operative monitoring.
High-sensitivity CRP measures the same protein but at much lower concentrations, and is used for something different: as one input into cardiovascular risk assessment in people who are otherwise well. Ordering hs-CRP in someone with an active infection tells you nothing useful, and ordering standard CRP for cardiovascular risk assessment lacks the resolution. Ask which one your doctor wants.
What a raised result should and should not trigger
In someone with symptoms, a raised marker supports the clinical picture and is useful for following the response to treatment. In someone without symptoms, a mildly raised CRP or ESR is a weak signal — a recent minor infection, obesity, smoking, or nothing identifiable at all.
The wrong response is a scan of everything. The right one is your doctor putting it alongside your history and examination and deciding whether it points anywhere. Very high levels are a different matter and do warrant a focused search for a cause.
One practical caution: a normal CRP does not exclude serious disease. Some significant conditions, including certain infections and cancers, can run with normal markers. Markers support a clinical judgement; they do not replace one.
This article is general health information, not a diagnosis or a treatment plan. Test results are read alongside your symptoms and history — please discuss yours with your doctor. See our disclaimer.
