C-reactive protein (CRP): reference ranges

In shortMost healthy adults have less than 0.3 mg/dL (3 mg/L). Above 1 mg/dL (10 mg/L) the rise is moderate; above 10 mg/dL (100 mg/L) it is marked.

Reference ranges

Group	Reference range
Most healthy adults	Less than 0.3 mg/dL (3 mg/L)
Healthy amount (general guide)	0.8–1.0 mg/dL (8–10 mg/L) or lower
Moderate increase	1–10 mg/dL (10–100 mg/L)
Marked increase	More than 10 mg/dL (100 mg/L)

Normal CRP values vary from lab to lab and often increase slightly with age and female sex. Whether a minor rise of 0.3–1 mg/dL (3–10 mg/L) is a cause for concern is unclear — the hs-CRP assay is used to look closer.

Check your value

Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.

A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.

What this marker is

C-reactive protein (CRP) is produced by the liver, and its level rises when there is inflammation in the body. It belongs to a group of proteins called acute phase reactants, which go up in response to inflammatory proteins (cytokines) produced by white blood cells during inflammation.

The CRP test is a general test for inflammation — not a specific one. It can reveal that inflammation is present somewhere in the body, but it cannot pinpoint the location or the reason. That is why it is often done together with the ESR (erythrocyte sedimentation rate) test, which looks for inflammation too, and why a high result leads to further tests rather than to a diagnosis.

Providers use CRP to check for flare-ups of inflammatory diseases such as rheumatoid arthritis, lupus, or vasculitis, and to see whether an anti-inflammatory medicine is working. A separate, more sensitive version — the high-sensitivity CRP (hs-CRP) assay — measures very small increases and is used to estimate the risk of heart disease: below 1.0 mg/L (0.1 mg/dL) is low risk, 1.0–3.0 mg/L (0.1–0.3 mg/dL) average, and above 3.0 mg/L (0.3 mg/dL) high.

No special preparation is needed: the blood sample is taken from a vein at any time. The level often increases slightly with age and female sex, and positive results also occur during the last half of pregnancy and with birth control pills — context the provider factors in.

When it is high

InfectionBacterial and viral infections are among the most common reasons for a clearly raised CRP.

Autoimmune and inflammatory diseaseRheumatoid arthritis, lupus, and related diseases raise CRP, and the test is used to track their flare-ups. Inflammatory bowel disease and rheumatic fever are on the list too.

Heart attackA heart attack injures heart tissue, and CRP rises in response.

CancerCancer is among the listed causes of a high CRP.

Everyday and hormonal influencesObesity, insomnia, depression, menopause hormone therapy, the last half of pregnancy, and birth control pills can all push the level up. Females often have slightly higher CRP than males.

When it is low

Low is the normal stateHealthy people have very low amounts of CRP, and there is no “lower than normal” problem — a low value is simply a quiet result.

Low does not exclude inflammationA low CRP does not always mean there is no inflammation: levels may not be increased in people with rheumatoid arthritis and lupus, for reasons that are unknown.

What can skew the result

These factors can shift the value without any disease — worth considering before a retest:

Age and female sex (slightly higher)Pregnancy (last half) and birth control pillsObesity, insomnia, depressionMenopause hormone therapy

How to prepare

No special steps are needed to prepare for this test. Tell your provider about the medicines you take, including hormone therapy and birth control pills.

When a retest makes sense

Because the level varies over time, a reading that matters is usually confirmed with a repeat test. In inflammatory diseases the trend over time — up in a flare, down when treatment works — is the real signal.

Who usually reviews this result

A result outside the reference range is usually reviewed by: your GP or primary care doctor; a rheumatologist if an autoimmune disease is suspected. Bring your lab report and any previous results to the appointment.

Names used on lab reports

Your report may use any of these names:
CRPC-reactive proteinhs-CRPAcute phase reactant

Units and conversion

Measured in: mg/dL

mg/dL = mg/L

mg/dL × 10 = mg/L. Example: 0.5 mg/dL = 5 mg/L. Results are rounded to 2 decimal places.

Several markers on your report?

See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.

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Frequently asked questions

What is the difference between CRP and hs-CRP?

Both measure the same protein. The standard CRP test detects inflammation from infections and disease; the high-sensitivity hs-CRP assay measures very small increases and is used to estimate heart-disease risk. They answer different questions and are not interchangeable.

If CRP is high, what do I have?

The test cannot say. CRP shows that inflammation is present somewhere, but not where or why — infection, autoimmune disease, heart attack, cancer, and even pregnancy or obesity can raise it. Your provider combines it with symptoms, history, and other tests to find the cause.

Can CRP be normal during inflammation?

Yes. Levels may not be increased in people with rheumatoid arthritis and lupus, for reasons that are unknown. A low CRP reassures but does not fully exclude inflammation.

Sources

C-Reactive Protein (CRP) Test: MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
C-reactive protein: MedlinePlus Medical Encyclopedia — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.

C-reactive protein (CRP)