CRP blood test: what it measures and what your result means

Medically reviewed by Dr Lebeth Jacob · 21 October 2026

Quick answer: CRP (C-reactive protein) is made by your liver when there is inflammation in your body. A CRP blood test shows whether inflammation is present and roughly how much. A high result is most often caused by an infection or injury, but can also come from conditions such as arthritis. CRP shows that inflammation is there, not where it is.

What is CRP?

When your body fights an infection or repairs damage, your liver releases CRP into the blood. Levels can rise within hours and fall again as the problem settles. That makes CRP useful for spotting inflammation and for checking whether treatment is working.

There are two versions of the test:

  • Standard CRP picks up the higher levels seen with infection and inflammatory illness.
  • High-sensitivity CRP (hs-CRP) measures much lower levels. It is used to look for low-grade inflammation that is linked to heart and circulation risk.

Why is CRP tested?

  • You have signs of infection or have been feeling unwell for a while
  • You have joint pain, stiffness or swelling
  • You have an inflammatory condition, such as rheumatoid arthritis or inflammatory bowel disease, and want to track it
  • You want to understand your heart risk alongside cholesterol (hs-CRP)
  • You are carrying extra weight, smoke, or have type 2 diabetes, which can all keep inflammation raised

What does a high CRP result mean?

A high CRP means inflammation is present somewhere in your body. Common reasons are:

  • Infections, especially bacterial infections such as chest or urine infections
  • A recent injury, operation or dental work
  • Inflammatory conditions such as rheumatoid arthritis or Crohn's disease
  • Hard exercise in the past day or two
  • Long-term low-grade inflammation linked to extra weight, smoking, poor sleep or diabetes
  • Less often, some cancers

A slightly raised hs-CRP in someone who feels well usually points to low-grade inflammation rather than an acute illness.

What does a low CRP result mean?

A low CRP is normal and means there's no sign of significant inflammation. For hs-CRP, lower is linked to lower heart risk.

What can affect your result?

  • A cold, infection, injury or vaccination in the past two weeks can raise CRP
  • Hard exercise in the day or two before the test can raise it
  • Pregnancy, and hormonal contraception or HRT, can raise hs-CRP
  • Statins and some anti-inflammatory medicines can lower it
  • For hs-CRP, test when you're well. If it comes back raised, a doctor may repeat it a few weeks later.

When to see a GP

Your results report shows the laboratory's normal range and flags any result outside it. Speak to your GP if:

  • Your CRP is flagged high and you don't know why
  • It stays high on a repeat test
  • You also have a fever, night sweats, unexplained weight loss or swollen joints

Call 999 or go to A&E if you feel very unwell with signs of sepsis: confusion, fast breathing, mottled or blue skin, or a rash that doesn't fade when pressed.

How we test CRP

You can have CRP tested with a blood sample taken at one of our 250+ partner clinics. High-sensitivity CRP is also available as a finger-prick kit at home. Samples are analysed by a UKAS-accredited laboratory. Results are usually ready in 3–5 working days, with a doctor's comments on every result.

Tests that include CRP

Prices for in-clinic tests include your appointment. Compare every test with CRP in the biomarker explorer

Frequently asked questions

How much CRP is dangerous?

There is no single dangerous number. A very high CRP usually means a significant infection or inflammation that needs prompt medical assessment, especially if you feel unwell. A mildly raised result in someone who feels well is less urgent, but should still be discussed with a GP.

What infections cause high CRP?

Bacterial infections, such as pneumonia, kidney infections and skin infections, tend to raise CRP the most. Viral infections like colds usually raise it less.

Can CRP detect cancer?

No. Some cancers raise CRP, but so do many other things. A high CRP on its own can't diagnose or rule out cancer.

What is the difference between CRP and hs-CRP?

They measure the same protein. Standard CRP is used to detect infection and inflammation. hs-CRP measures much lower levels and is used to assess heart and circulation risk.

How can I lower my CRP?

Treating the cause comes first. For long-term low-grade inflammation, losing extra weight, being active, stopping smoking, sleeping well and eating plenty of vegetables, fruit, whole grains and oily fish can all help.

What is the difference between CRP and ESR?

Both show inflammation. CRP changes quickly, within hours to days. ESR changes more slowly, so doctors sometimes use both.