Key takeaways
- CRP (C-reactive protein) is a protein your liver releases when there's inflammation or infection somewhere in the body.
- A raised CRP shows that inflammation is present. Your symptoms and other results help show where it's coming from and why.
- CRP rises and falls faster than ESR, which makes it useful for tracking how quickly inflammation is changing.
- High-sensitivity CRP measures the same protein at much lower levels, to look at low-grade inflammation linked to heart health.
- CRP can be normal early in an illness, so it works best as one part of a wider assessment.
Perhaps a doctor has mentioned checking your inflammatory markers. Or a report has come back with CRP flagged and no explanation beside it.
CRP (C-reactive protein) is a protein your liver releases into the blood when there's inflammation or infection. A raised result shows that inflammation is present somewhere in the body. It doesn't say where or why, so it's always read together with your symptoms and other results. A CRP blood test is a common starting point when a clinician wants to check whether inflammation is there at all.
Book a CRP blood test at 117a Harley Street: £70 plus the £50 blood draw, results in 1 day.
What does a CRP test measure?
It measures the level of C-reactive protein circulating in your blood. Your liver makes more of it whenever the immune system detects inflammation or infection. That could be a bacterial infection, a viral illness, an injury or an ongoing inflammatory condition. Because so many things can trigger it, CRP is described as non-specific. A raised result confirms that inflammation is happening, without pointing to a single cause.
What can a high CRP result mean?
A high CRP can mean an active infection, an inflammatory condition, or recent tissue damage from injury or surgery. The level can rise sharply within hours of the trigger starting, which is why CRP is good at picking up acute inflammation quickly.
How high the result is, and how it changes over time, usually tells a clinician more than a single reading. They'll interpret it alongside your symptoms, an examination and any other tests.
If you feel very unwell, have a high temperature, or have symptoms such as confusion, a stiff neck or difficulty breathing, get medical help the same day through NHS 111, or call 999 in an emergency.
Can CRP be normal when something is wrong?
Yes. CRP can be normal early in an illness, before the inflammatory response has built up. Some conditions also provoke very little CRP rise. A normal result can't rule out every cause of your symptoms, so CRP is used as one part of an assessment rather than a yes-or-no answer.
CRP vs ESR: what's the difference?
CRP and ESR (erythrocyte sedimentation rate) both act as general markers of inflammation. They behave differently, so they're read together rather than swapped for one another.
| CRP | ESR | |
|---|---|---|
| Speed of change | Rises and falls quickly, often within hours to days | Rises over days and can take weeks to fall |
| What it's good for | Tracking how fast inflammation is changing | A general, longer-running picture of inflammation |
| Price at Blood London | £70 | £43.75 |
| Turnaround | 1 day | 1 day |
Because CRP responds faster, it's often the marker used to see whether inflammation is settling after treatment. ESR adds a broader picture, particularly for longer-running inflammatory conditions.
Standard CRP vs high-sensitivity CRP
Both measure the same protein, but high-sensitivity CRP is calibrated to detect much lower levels. Standard CRP looks for infection or significant inflammation, where the result should be clearly raised if something is going on. High-sensitivity CRP looks at low-grade inflammation linked to cardiovascular risk, at levels too low for the standard test to separate usefully. The standard test and the high-sensitivity CRP test each cost £70, with results in 1 day.
When to repeat a CRP test
CRP is often repeated to see whether it's rising, falling or holding steady, because the direction of change can matter more than a single number. Your clinician can advise on timing. That depends on what the test was checking: a known infection, recovery after treatment, or an unexplained raised result.
If your CRP is part of a wider look at your blood, a haematology profile (FBC and ESR) adds useful context for £75, with results in 1 day. A full blood count on its own is £63.75, also in 1 day. Both are plus the £50 blood draw.
If you'd like a doctor to explain your result, add a doctor review to your test for £75. If a raised CRP has no clear explanation, a private GP consultation at Medical Express Clinic (£150) can help decide what to check next.
Booking a CRP test at 117a Harley Street
CRP usually needs no special preparation, such as fasting. If you're having other tests at the same visit, check each test page, as some do need fasting. Results usually arrive by email in 1 day. Like all our private blood tests in London, you can book online or walk in to 117a Harley Street seven days a week, without a GP referral. Start your booking.
Frequently asked questions
Do I need to fast for a CRP test?
Not usually. Eating doesn't affect CRP, but if you're having other tests at the same visit, check each test page, as some do need fasting.
How quickly do CRP results come back?
Usually in 1 day, sent to you by email.
Can a cold raise my CRP?
Yes. Colds and other viral illnesses trigger an inflammatory response, so they can raise CRP, though the rise is often smaller than with a bacterial infection.
Is CRP a cancer test?
No. CRP is a non-specific marker of inflammation that many different conditions can raise, so it isn't used on its own to look for or rule out cancer.
What is the difference between CRP and hs-CRP?
They measure the same protein, but hs-CRP is calibrated to pick up much lower levels. That makes it useful for assessing low-grade inflammation linked to heart health rather than detecting infection.
Should I test CRP and ESR together?
It depends on what's being investigated. A haematology profile gives you a full blood count and ESR in one visit, and your clinician can advise whether adding CRP gives a fuller picture.
References
- NHS: Blood tests
- Lab Tests Online UK: C-reactive protein (CRP)
- Lab Tests Online UK: Erythrocyte sedimentation rate (ESR)