Inflammation
CRP blood test
A CRP (C-reactive protein) blood test measures a protein your liver releases when there is inflammation in the body. It rises within hours of infection, injury or a flare of an inflammatory condition and falls as things settle, which makes it a useful, general marker of how much inflammation is present, though not of its cause.
- What it measures
- C-reactive protein, a general marker of inflammation
- Sample
- Venous blood sample
- Fasting
- Not required
- Also known as
- C-reactive protein, hs-CRP, high-sensitivity CRP
- Included in 57 Health tests
- 4 panels, from £100
CRP reference range
Guide only| Category | Guide range |
|---|---|
| Normal (adults) | < 5 mg/L |
CRP rises within hours of inflammation, infection or injury and falls as it resolves, so it shows the presence and degree of inflammation, not its cause. High-sensitivity CRP (hs-CRP) measures very low levels for cardiovascular risk context: under 1 mg/L is lower relative risk, 1–3 average, and over 3 higher.
These are general UK adult guide ranges from public health sources, shown for orientation only. Reference ranges vary by laboratory, assay, age and sex, so your result is always interpreted against the range quoted by the analysing laboratory on your report.
What does a high CRP level mean?
A high CRP means there is active inflammation somewhere in the body, commonly from an infection, an injury, recent surgery, or a flare of an inflammatory or autoimmune condition. A markedly high CRP more often points to a bacterial infection.
CRP does not show where the inflammation is or what is causing it, so a raised result is interpreted alongside your symptoms and, where needed, further tests.
What does a low CRP level mean?
A low or normal CRP is reassuring against significant active inflammation at the time of the test.
It doesn't rule out every condition (some low-grade or localised problems can occur with a normal CRP), so it's read together with your symptoms and other results.
When to consider a CRP test
- Suspected infection or unexplained fever
- Monitoring a known inflammatory or autoimmune condition
- Unexplained fatigue or feeling persistently unwell
- Cardiovascular risk assessment (hs-CRP)
- After surgery or injury, to track recovery
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. A CRP test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.