Say you have had a nagging sore throat for two weeks and your lab result shows a CRP of 18. Sounds alarming, until you know where that number comes from: your liver pumps CRP into the bloodstream as soon as there is inflammation anywhere. The number tells you something is going on, but not what or where. That distinction is exactly what this article is about.
My stance up front: CRP is brilliant as an alarm bell and useless as a diagnosis. Read a raised CRP out of context and you only scare yourself. Always read it together with your symptoms and your other values.
What is CRP?
C-reactive protein is an acute-phase protein. Your body makes it quickly in response to infection, inflammation or tissue damage. It is a sensitive but non-specific marker: it reports that there is inflammation, not the cause. That broad sensitivity is exactly what makes CRP so useful as a signal value, often one of the first signs something is happening.
Normal CRP values per range
CRP is measured in mg/L. The table below is your decision aid: per range you see what it usually means and a logical next step. These limits are guide values; your doctor always assesses the full picture.
| CRP (mg/L) | Interpretation | What it often means | Next step |
|---|---|---|---|
| Below 5 | Normal | No sign of significant inflammation | No action needed |
| 5 to 10 | Mildly raised | Mild infection, light or chronic inflammation | Check context, possibly repeat |
| 10 to 50 | Moderately raised | Active inflammation or infection | Discuss with your GP |
| 50 to 200 | Strongly raised | Serious infection or inflammation | Medical assessment |
| Above 200 | Very strongly raised | Possible sepsis or extensive tissue damage | Assess urgently |
What can a raised CRP level mean?
The causes split roughly into acute and chronic.
Acute causes
- Infections: bacterial infections often cause a sharp rise, viral ones a milder one.
- Injuries or surgery: tissue damage activates the inflammatory response.
- Acute inflammation: for example pneumonia or appendicitis.
Chronic causes
- Autoimmune disease: rheumatoid arthritis, Crohn's disease, lupus.
- Obesity: fat tissue produces inflammatory substances that can raise CRP.
- Smoking: chronic low-grade inflammation.
- Cardiovascular disease: low-grade inflammation plays a part in atherosclerosis.
hs-CRP: the sensitive variant for heart risk
Alongside standard CRP there is hs-CRP (high-sensitivity CRP). It measures the same marker, but far more precisely in the low range, and is used to estimate your cardiovascular risk. The Dutch Heart Foundation (Hartstichting) names chronic low-grade inflammation as one of the factors involved in cardiovascular disease.
- Below 1 mg/L: low cardiovascular risk.
- 1 to 3 mg/L: average risk.
- Above 3 mg/L: raised risk, provided there is no acute infection.
Important: do not measure hs-CRP just after a cold or flu. An acute infection temporarily spikes the value and makes the heart-risk estimate unreliable. To map heart risk more broadly, look at the lipid panel and read our pillar on which blood values determine your heart risk.
CRP versus ESR: two inflammation markers side by side
On a result you sometimes see CRP and ESR (the sedimentation rate) listed together. Both measure inflammation, but they behave differently over time. CRP rises and falls quickly: it is raised within hours and drops just as fast once the cause disappears. The ESR reacts more slowly and stays high for longer. So the combination complements itself: a high CRP with a still-normal ESR fits a freshly started inflammation, while a high ESR with an already-fallen CRP can point to the aftermath. Your doctor uses this difference to estimate which phase an inflammation is in.
What do you do with a raised CRP value?
First check whether there is an obvious cause: a recent cold, injury or surgery. If CRP stays raised with no clear reason, discuss it with your GP, who can request targeted follow-up. If the rise is mainly lifestyle-related, working on weight, diet and quitting smoking helps, in line with the Hartstichting and the Netherlands Nutrition Centre (Voedingscentrum).
One important note: a one-off, mildly raised CRP without symptoms is rarely a reason for extensive investigation. Reference ranges apply to the average healthy population, and an incidental mild rise after a busy week or a cold is common. A repeat measurement after a few weeks shows whether it is a lasting rise or a passing peak. Only with a persistently or markedly raised CRP, or CRP together with symptoms, does looking further become worthwhile.
Frequently asked questions
Do I need to fast for a CRP test?
No, fasting is not needed. You can have blood drawn at any time of day.
Can stress raise my CRP?
Chronic stress can lead to low-grade inflammation and raise your CRP slightly. Acute stress usually has no direct effect.
How fast does CRP fall after an infection?
CRP falls quickly once the cause is gone: it halves roughly every 18 to 20 hours. Within a week of recovery your CRP is usually normal again.
Sources
- Hartstichting (Dutch Heart Foundation). Inflammation and risk factors for cardiovascular disease. Accessed 2026.
- NHG (Dutch College of General Practitioners). Diagnostics for infection and inflammation markers. Accessed 2026.
- Voedingscentrum (Netherlands Nutrition Centre). Healthy weight and diet. Accessed 2026.
Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. Always discuss treatment decisions with your own GP.
Frequently asked questions
Do I need to fast for a CRP test?
No, fasting is not required for a CRP measurement. You can have blood drawn at any time of day.
Can stress raise my CRP level?
Chronic stress can contribute to low-grade inflammation, which may slightly raise CRP. Short-term, acute stress usually has no direct effect on your CRP.
How quickly does CRP drop after an infection?
CRP drops fairly quickly once the cause resolves. The value roughly halves every 18 to 20 hours, so CRP is usually back to normal within a week of recovery.
What is the difference between CRP and the sedimentation rate?
Both are inflammation markers. CRP responds faster to inflammation and also falls faster, while the sedimentation rate changes more slowly. Doctors sometimes review them together.
Can a common cold raise my CRP?
Yes, a cold or flu can also raise CRP. Viral infections usually cause a milder rise than bacterial infections.
What is a dangerously high CRP level?
There is no fixed cut-off for danger. Values above 50 to 100 mg/L more often fit a serious infection or inflammation. A significantly elevated value is a reason to discuss it with your GP.
Can a CRP value be too low?
No, a low CRP value is not harmful. A value below 5 mg/L falls within the normal range and usually indicates that no significant inflammation is present.
Do medications affect my CRP level?
Some medications, such as anti-inflammatory drugs, can affect CRP. For that reason it helps to mention which medications you use when having a blood test.
How often can you have your CRP measured?
There is no fixed rule for how often to measure CRP. How often is worthwhile depends on your situation and is something to discuss with your GP.
Does a CRP value say anything about cancer?
CRP is not a cancer test. The value can be elevated in a wide range of conditions and says nothing specific about cancer on its own. Discuss persistently elevated values with your GP.
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Vitalcheck
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