Key takeaways
- CRP (C-reactive protein) is a protein your liver releases when there is inflammation or infection somewhere in the body.
- A raised CRP shows that inflammation is present, but not where it is coming from or why, so it is read alongside your symptoms and other test results.
- CRP can be normal even when something is wrong, particularly early on or with conditions that don't trigger a strong inflammatory response.
- At Blood London a CRP test costs £70 plus the £50 blood draw, with results in 1 day.
- CRP rises and falls faster than ESR, which makes it more useful for tracking how quickly inflammation is changing.
- High-sensitivity CRP is a more sensitive version of the same test, used to look at lower-level inflammation linked to heart health rather than to detect infection.
CRP (C-reactive protein) is a protein your liver releases into the blood when there is inflammation or infection. A raised result shows that inflammation is present somewhere in the body, but on its own it doesn't say where or why, so it is always read together with your symptoms and other test results. A CRP blood test is a common starting point when a clinician wants to check whether inflammation is present 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?
A CRP test measures the level of C-reactive protein circulating in your blood. Your liver produces more of this protein when the immune system detects inflammation or infection anywhere in the body, whether that's from a bacterial infection, a viral illness, an injury, or an ongoing inflammatory condition. Because CRP is made in response to a wide range of triggers, the test is described as non-specific: a raised result confirms that inflammation is happening, without pointing to a single cause by itself.
What can a high CRP result mean?
A high CRP result 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 part of why CRP is useful for picking up acute inflammation quickly. How high the result is, and how it changes over time, is usually more informative than a single reading on its own, which is why your clinician will interpret it alongside your symptoms, 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 even when there is an underlying problem, particularly in the early stages of an illness before the inflammatory response has built up, or with conditions that don't provoke a strong CRP rise. A normal CRP doesn't rule out every possible cause of your symptoms, which is why it is used as one part of an assessment rather than a test that gives a yes or no answer on its own.
CRP vs ESR: what's the difference?
CRP and ESR (erythrocyte sedimentation rate) both act as general markers of inflammation, but they behave differently and are read together rather than as substitutes 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 plus the £50 blood draw | £43.75 plus the £50 blood draw |
| Turnaround | 1 day | 1 day |
Because CRP responds faster, it is often the marker used to see whether inflammation is settling after treatment, while ESR can add a broader picture, particularly for longer-running inflammatory conditions.
Standard CRP vs high-sensitivity CRP
Standard CRP and high-sensitivity CRP measure the same protein, but high-sensitivity CRP is calibrated to detect much lower levels. Standard CRP is generally used to look for infection or significant inflammation, where the result is expected to be clearly raised if something is going on. High-sensitivity CRP is instead used to look at low-grade inflammation linked to cardiovascular risk, at levels too low for the standard test to distinguish usefully. The standard CRP test and the high-sensitivity CRP test each cost £70 plus the £50 blood draw, with results in 1 day.
When to repeat a CRP test
CRP is often repeated to see whether it is rising, falling or holding steady, since the direction of change can be more useful than a single number. Your clinician can advise on timing based on what the test was originally checking, whether that's monitoring a known infection, watching recovery after treatment, or following up on an unexplained raised result. If your CRP was checked as part of a wider blood picture, a haematology profile (FBC and ESR) alongside it can add useful context (£75 plus the £50 blood draw, results in 1 day). A full blood count on its own costs £63.75 plus the £50 blood draw, with results in 1 day. If you would like a doctor to explain your result, you can 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
A CRP test at Blood London costs £70 plus the £50 blood draw, with results usually available in 1 day by email. No special preparation, such as fasting, is usually needed for CRP; if you are having other tests at the same visit, check each test page, as some do need fasting. 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.
Book a CRP blood test or high-sensitivity CRP test online, or walk in seven days a week: £70 plus the £50 blood draw. Start your booking.
Frequently asked questions
Do I need to fast for a CRP test?
Not usually. CRP is not affected by eating, but if you are having other tests at the same visit, check each test page, as some do need fasting.
How quickly do CRP results come back?
Results are usually available in 1 day and are sent to you by email.
Can a cold raise my CRP?
Yes. Common infections, including colds and other viral illnesses, can raise CRP because they trigger an inflammatory response, though the rise is often smaller than with a bacterial infection.
Is CRP a cancer test?
No. CRP is not a cancer test. It's a non-specific marker of inflammation that can be raised by many different conditions, 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, which 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 is one way to get a full blood count and ESR together in one visit; your clinician can advise whether adding CRP gives a fuller picture for your situation.
References
- NHS: Blood tests
- Lab Tests Online UK: C-reactive protein (CRP)
- Lab Tests Online UK: Erythrocyte sedimentation rate (ESR)