Biomarker Glossary
CRP
C-reactive protein (CRP) is a protein made by the liver in response to inflammation in your body. A CRP blood test is the most widely used UK marker of acute and chronic inflammation, used to investigate infection, autoimmune disease, cardiovascular risk and general inflammatory burden.
Also known as: C-Reactive Protein, hs-CRP, High Sensitivity CRP
CRP is most informative when read alongside related markers like Ferritin and ALT. A single number rarely tells the whole story. If your reading sits outside the typical range, share the full report with your GP or healthcare professional before drawing conclusions.
What is CRP?
CRP rises within hours of inflammation, infection or tissue damage and falls back to normal as the trigger resolves. It is part of the body's innate immune response and a sensitive (although non specific) marker that something is going on.
Standard CRP tests detect levels above about 5 mg/L and are used for acute illness or chronic inflammation. High sensitivity CRP (hs-CRP) detects very low levels (below 5 mg/L) and is used to assess long term cardiovascular risk from low grade chronic inflammation.
Because CRP rises with so many conditions, it does not tell you what is causing inflammation. It is a screening signal that often prompts further investigation.
Why test CRP?
- To investigate symptoms of infection, joint pain, fatigue or unexplained illness.
- To monitor autoimmune conditions such as rheumatoid arthritis, lupus or inflammatory bowel disease.
- As a cardiovascular risk marker (hs-CRP).
- To track the impact of lifestyle changes on chronic inflammation.
- Alongside ferritin, ESR and other markers to investigate persistent fatigue or unexplained symptoms.
To investigate symptoms of infection, joint pain, fatigue or unexplained illness.
CRP normal range (UK)
| Result | What it means |
|---|---|
| Below 1.0 mg/L (hs-CRP) | Low cardiovascular risk |
| 1.0 to 3.0 mg/L (hs-CRP) | Average cardiovascular risk |
| Above 3.0 mg/L (hs-CRP) | High cardiovascular risk, or recent infection |
| Below 5 mg/L (standard CRP) | Normal |
| 5 to 40 mg/L | Mild to moderate inflammation. Common in chronic infection, autoimmune disease, recent injury. |
| Above 40 mg/L | Significant inflammation. Often bacterial infection, severe injury or active autoimmune flare. |
For cardiovascular risk assessment, use high sensitivity CRP (hs-CRP) and test on a day when you are not unwell. A recent cold or vaccine can transiently raise CRP and skew the result.
About these ranges. The ranges above are typical UK clinical lab ranges aligned to NHS and Royal College of Pathologists guidance. Your Chxhealth report will show the specific reference range used by our partner lab, Randox, for each marker. Lab ranges vary slightly between providers and assays. Always interpret your results in the context of the range printed on your own report.
What causes high CRP?
- Acute infection (bacterial more than viral)
- Autoimmune disease (rheumatoid arthritis, lupus, inflammatory bowel disease)
- Chronic low grade inflammation (obesity, metabolic syndrome, smoking)
- Recent injury, surgery or burns
- Cancer in some cases
- Severe stress
- Following a vaccine for a few days
What causes low CRP?
- CRP is normally low (below 1 mg/L) in healthy adults.
- Very low CRP is not clinically significant on its own.
Symptoms of high CRP
- Symptoms depend on the underlying cause: fever, fatigue, joint pain, infection signs.
- Chronic low grade CRP elevation often has no symptoms but is linked to higher long term cardiovascular risk.
Symptoms of low CRP
- Low CRP is normal and asymptomatic.
How is CRP tested?
CRP is measured from a small blood sample. No fasting is required.
For cardiovascular risk assessment, use high sensitivity CRP (hs-CRP).
Do not test if you have had a cold, vaccine or injury within the past 2 weeks, as this can falsely raise CRP.
Chxhealth samples are analysed by Randox, a UK laboratory accredited by UKAS. Results return in 3 to 5 working days.
How to support healthy CRP levels
- Reduce visceral fat through diet and exercise. Excess abdominal fat is one of the biggest drivers of low grade inflammation.
- Eat more anti inflammatory foods: oily fish, olive oil, leafy greens, berries, nuts, beans, turmeric.
- Reduce ultra processed foods, refined sugar and seed oils high in omega 6.
- Stop smoking. Smoking is a major driver of chronic CRP elevation.
- Prioritise sleep and manage stress. Both directly affect inflammation.
- Treat dental, gut and other infections, which can quietly raise CRP for years.
These are general lifestyle suggestions. Chxhealth is an information service. For personal medical advice, please speak to a healthcare professional.
Chxhealth panels that test CRP
9 Chxhealth biomarker panels include CRP. Each is analysed by Randox, a UK laboratory accredited by UKAS. Reports are delivered in 3 to 5 working days.
- Acute Med 2
- Advanced GP2
- Advanced GP3
- Fertility Panel
- Inflammation
- Long Covid
- Sports Performance
- Tired All The Time
- Athletic Performance Panel
CRP FAQs
What is a normal CRP level?
Below 5 mg/L on a standard CRP test, or below 1 mg/L on high sensitivity CRP (hs-CRP). Higher levels suggest acute infection, autoimmune disease or chronic low grade inflammation.
What is the difference between CRP and hs-CRP?
They measure the same protein, but hs-CRP uses a more sensitive assay that can detect very low levels. Use hs-CRP for cardiovascular risk and CRP for acute or significant inflammation.
Can CRP be raised without an obvious cause?
Yes. Chronic low grade CRP elevation is often linked to obesity, smoking, periodontal disease, sleep apnoea or chronic low grade infections that may have no obvious symptoms.
How fast does CRP fall?
After an acute infection or injury, CRP typically halves every 18 to 24 hours once the trigger resolves. Persistent elevation more than 4 to 6 weeks after an event suggests an ongoing process.
Should I worry about a slightly raised CRP?
A persistently raised CRP between 3 and 10 mg/L without an obvious cause is worth investigating, particularly to address cardiovascular risk and rule out chronic infection or autoimmunity.
Often tested with CRP
The biomarkers below are commonly investigated alongside CRP because they reveal connected aspects of the same physiological picture:
- Ferritin: Ferritin is also an acute phase reactant. CRP helps interpret raised ferritin.
- ALT: Liver involvement in systemic inflammation often raises ALT.
- GGT: Another marker that rises with hepatic inflammation.
- Haemoglobin: Chronic inflammation can produce anaemia of chronic disease.
Choose the right test for your goal
If you are reading about CRP because of a specific health goal, our buying guides walk you through which Chxhealth panels fit:
Sources and further reading
This page is informed by guidance from the NHS, NICE, Royal College of Pathologists and other UK authoritative bodies. For deeper detail or to verify the information, see:
- NHS: Blood tests
- Versus Arthritis: Inflammation markers
- NICE: Inflammation in rheumatoid arthritis
- Lab Tests Online UK: C-Reactive Protein (CRP)
About this page. Last reviewed: 13 May 2026. Next scheduled review: May 2027. This page has not yet been independently reviewed by a clinician. It is written from authoritative UK medical guidance (NHS, NICE, Royal College of Pathologists, peer-reviewed sources) but has not undergone formal clinical sign off.
Important. Chxhealth is a UK information service. We do not diagnose, treat or prescribe. The reference ranges and information on this page are general educational content and should not be used as a substitute for advice from a qualified healthcare professional. For any concerns about your health or results, please speak to your GP or another healthcare professional.