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High CRP: what your C-reactive protein result means
CRP is a protein made by the liver when there is inflammation in the body. Here is how to read your CRP value, what can raise it and when a high result needs attention.
This guide is general information and does not replace medical advice. Reference ranges differ between laboratories – always compare your result with the range printed on your own report and discuss abnormal results with a doctor.
C-reactive protein (CRP) is produced by the liver in response to inflammation. It is not specific – it does not tell where the inflammation is or what causes it – but it is a sensitive and fast marker. Doctors use it to detect infection or inflammation and to follow how a condition responds to treatment.
Normal CRP levels
CRP is usually reported in mg/L. Most laboratories regard a value below 5 mg/L as normal (some use below 10 mg/L). Always check the reference range printed on your own report.
| CRP (mg/L) | What it often means |
|---|---|
| below 5 | Normal – no significant inflammation detected |
| 5–10 | Slightly raised – minor infection, smoking, obesity, recent exercise or injury |
| 10–40 | Mild to moderate inflammation – often a viral infection or a flare of a chronic condition |
| 40–200 | Marked inflammation – often a bacterial infection or active inflammatory disease |
| above 200 | Severe inflammation – serious bacterial infection, major trauma or burns; needs prompt medical assessment |
These bands are only a rough guide. A viral infection can occasionally push CRP above 100 mg/L, and some serious conditions show only a modest rise.
Common causes of a high CRP
- Infections – bacterial infections (for example pneumonia, urinary tract infection) usually raise CRP more than viral ones.
- Inflammatory diseases – rheumatoid arthritis, inflammatory bowel disease, vasculitis and other autoimmune conditions.
- Tissue damage – surgery, injury, burns, heart attack.
- Lifestyle factors – smoking, obesity, poor sleep and diabetes keep CRP slightly raised over the long term.
- Some cancers can also raise CRP; a persistently raised value without explanation should be investigated.
hs-CRP and heart risk
A high-sensitivity CRP (hs-CRP) test measures very low CRP levels and is sometimes used to refine cardiovascular risk in people without acute illness. Following the American Heart Association and CDC: below 1 mg/L means lower risk, 1–3 mg/L average risk and above 3 mg/L higher risk. The test should be repeated, and it is not meaningful during an infection.
CRP or ESR?
The erythrocyte sedimentation rate (ESR) is another inflammation marker. CRP rises and falls faster, so it reflects the current state better; ESR changes slowly and is also affected by age, anaemia and pregnancy. Doctors often request both.
When should you see a doctor?
- if your CRP is raised and you have fever, pain, swelling, a cough, urinary symptoms or feel unwell;
- if CRP stays raised on repeat tests without a clear reason;
- if you have unexplained weight loss, night sweats or long-lasting tiredness together with a raised CRP.
Seek urgent care for a very high CRP together with high fever, confusion, rapid breathing, severe pain or signs of sepsis.
Sources
- Lab Tests Online UK – C-reactive protein: labtestsonline.org.uk
- Pearson TA et al. Markers of inflammation and cardiovascular disease (AHA/CDC statement). Circulation 2003;107:499–511.
- Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest 2003;111:1805–1812.
- NICE – Fever in under 5s and Pneumonia in adults guidelines (use of CRP): nice.org.uk
Frequently asked questions
What CRP level is considered normal?
Most laboratories report a CRP below 5 mg/L (some use below 10 mg/L) as normal. A high-sensitivity CRP (hs-CRP) test, used for heart risk, measures much lower levels: below 1 mg/L is low risk, 1–3 mg/L average and above 3 mg/L higher risk.
Can stress or a cold raise CRP?
Yes. A common cold, a minor injury, heavy exercise, smoking or being overweight can all raise CRP moderately. That is why CRP must always be interpreted together with symptoms.
How quickly does CRP go down?
CRP rises within 6–8 hours of inflammation starting and peaks after about 2 days. Once the cause settles it falls fairly quickly – roughly halving every 19 hours – so a repeat test can show whether treatment is working.