Lab results explained
High CRP: what your result means
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Short answer: CRP (C-reactive protein) is usually under 5 mg/L, and a higher result means there is inflammation somewhere in the body. Infections are the most common cause, and very high values often point to a bacterial infection. CRP cannot show where the problem is, so your doctor reads it with your symptoms. hs-CRP is a separate heart risk test.
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Typical adult range
Your lab may print a slightly different range. Use the one on your report when there is one.
| Test | Men | Women |
|---|---|---|
| CRP (C-reactive protein) | under 5 mg/Lunder 0.5 mg/dL | |
| hs-CRP (heart risk) | Lower heart risk: under 1 mg/L Average heart risk: 1–3 mg/L Higher heart risk: 3–10 mg/L High (check for infection): 10 or more mg/L | |
| ESR | 0–15 mm/hr | 0–20 mm/hr |
What CRP measures
C-reactive protein is made by the liver and rises within hours of an infection, injury or inflammation. It also falls quickly once the problem settles, so doctors use it to track recovery. Most labs report CRP in mg/L. If your report shows mg/dL, multiply by 10 to get mg/L, so 0.5 mg/dL equals 5 mg/L. The high-sensitivity test (hs-CRP) measures very low levels and is used to judge heart risk in people who are otherwise well. Under 1 mg/L is lower risk, 1 to 3 is average and above 3 is higher.
Common causes of a high CRP
The size of the rise gives a rough guide. Mild rises can come from a cold, a minor injury, obesity or smoking. Higher values are more typical of a significant infection or an active inflammatory disease, but there is a lot of overlap. A CRP above 100 mg/L is often a bacterial infection, though not always, and some viral infections can push CRP that high too.
- Bacterial infections, such as pneumonia or urine infection
- Viral infections, usually with smaller rises
- Autoimmune conditions such as rheumatoid arthritis or lupus
- Inflammatory bowel disease
- Recent surgery, injury or burns
- Obesity, smoking and, less often, some cancers
CRP, hs-CRP and ESR
ESR (erythrocyte sedimentation rate) is another test of inflammation. It rises and falls more slowly than CRP, and it is also affected by age, anaemia and pregnancy. The usual ESR is up to 15 mm/hr for men and 20 for women on this checker. A high CRP with a normal ESR may mean a recent problem, while a high ESR with a normal CRP can happen in slower conditions. An hs-CRP above 10 mg/L usually means short-term inflammation, so it should not be used for heart risk until it is repeated after recovery.
What usually happens next
If you have clear symptoms such as a cough, fever or painful urination, your doctor will look for the infection and treat it. If you feel well and CRP is mildly high, the test may simply be repeated in a few weeks. A persistently high CRP without an obvious cause may lead to more tests, such as a blood count, urine test, chest X-ray or tests for autoimmune disease. CRP is also used to check whether treatment for an infection or inflammatory condition is working.
When to get help the same day
Get same-day medical care if a high CRP comes with fever and you feel very unwell, or with a hot swollen joint, severe belly pain, or a cough with breathlessness. Call your local emergency number for confusion, a stiff neck with fever, a rash that does not fade when pressed, very fast breathing, chest pain or collapse.
Questions to ask your doctor
- What do you think is causing my high CRP?
- Does the level suggest a bacterial infection?
- Should CRP or ESR be repeated, and when?
- Do I need other tests to look for the cause?
- Should my hs-CRP be used to judge my heart risk?
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Frequently asked questions
Is a CRP of 20 mg/L serious?
A CRP of 20 mg/L shows clear inflammation, often from an infection. Whether it is serious depends on how you feel and what else is found. Your doctor will look at your symptoms and may repeat the test to check it is falling.
What is the difference between CRP and hs-CRP?
Both measure the same protein. Standard CRP looks for inflammation and infection. hs-CRP picks up much lower levels and is used, along with cholesterol and other factors, to estimate heart disease risk in people without an active illness.
Can a viral infection raise CRP?
Yes. Viral infections usually cause smaller rises than bacterial ones, but the ranges overlap. CRP alone cannot tell a viral from a bacterial infection with certainty.
How fast does CRP come down?
CRP can halve every day or two once the cause is treated or settles. A falling CRP is a good sign that treatment is working. ESR takes longer to return to normal.
Sources
This page explains what results usually mean. It isn't a diagnosis or medical advice; your doctor interprets results with your symptoms, history and medicines. Medical disclaimer
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