C-Reactive Protein (CRP, incl. hs-CRP)
A protein your liver makes when the body has inflammation. Standard CRP helps check for infection or injury, and hs-CRP is used in heart-risk checks.
AI-verified against cited sources. Awaiting expert reviewAlso called CRP, hs-CRP, hsCRPLOINC 30522-7
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What it is
C-reactive protein (CRP) is a protein your liver releases into the blood when something sets off inflammation, such as an infection, an injury or a flare of a long-term condition. It can start rising within hours and falls quickly once the cause settles. Labs measure the same protein in two ways. The standard CRP test is built for the higher levels seen with infection and inflammation. The high-sensitivity test (hs-CRP) measures very small amounts, so it is used to look at low-grade inflammation in people who feel well, usually as part of a heart-health check.
Why it matters
CRP is a fast, general signal that inflammation is present. Clinicians use it to decide whether to look further, and to see whether treatment for an infection or an inflammatory condition is working. It can't tell where the inflammation is or what caused it. In heart-health checks, people with higher hs-CRP have more heart attacks and strokes on average in large studies. Some US guidelines list 2.0 mg/L or higher as one factor that can inform decisions, but experts still debate how much it adds to cholesterol, blood pressure and the other usual factors.
If it’s low
A low or very low CRP is the usual finding in people who are well, and it is not a problem. It means there is little sign of active inflammation right now. A low CRP doesn't rule out every inflammatory condition, though, because a few, such as lupus, can cause only a small CRP rise.
Common causes
- No active inflammation or infection (the usual reason)
- Taking a statin medicine, which lowers hs-CRP
- A few inflammatory conditions that cause only a small CRP rise, such as lupus
- Severe liver disease, which can limit how much CRP the liver makes
If it’s high
A higher CRP is a sign of inflammation or stress on tissues somewhere in the body. The cause is often short-term, such as a cold, a minor injury or a dental problem. Small rises (roughly 3 to 10 mg/L) are common and have many everyday causes. Values that stay above about 10 mg/L point to a more active process, such as an infection, an injury or a flare of a long-term condition, and your clinician will likely want to look into it, often by repeating the test. A high CRP doesn't say what the cause is, and it is not a diagnosis.
Common causes
- A recent cold, flu or other infection
- A minor injury, a dental or gum problem, or recent surgery
- Excess body weight, smoking or poor sleep
- Hormone therapy for menopause taken by mouth, birth control pills, or pregnancy (especially late pregnancy)
- Long-term inflammatory or autoimmune conditions, such as rheumatoid arthritis
- Bacterial infections or significant tissue injury, which can push CRP much higher
What can help
- If this was a heart-risk (hs-CRP) test, ask whether to repeat it at least 2 weeks after you've recovered from any illness
- Tell your clinician about recent illness, injury, dental work, surgery, new medicines and hormone therapy so they can put the number in context
- Not smoking, a healthy weight and good sleep are linked with lower CRP; ask your clinician what makes sense for you
- Ask whether gum or dental problems or another ongoing source of inflammation should be looked at
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–5 mg/L. Source: Mayo Clinic Laboratories (catalog page mirrored on testcatalog.org), ARUP Laboratories, Labcorp, MedlinePlus (National Library of Medicine), Journal of Clinical Investigation, American Journal of Medicine, Journal of the American College of Cardiology, Journal of Rheumatology, Frontiers in Immunology.
- Adults (this one applies)0–5 mg/L
Sources: Mayo Clinic Laboratories (catalog page mirrored on testcatalog.org), ARUP Laboratories, Labcorp, MedlinePlus (National Library of Medicine), Journal of Clinical Investigation, American Journal of Medicine, Journal of the American College of Cardiology, Journal of Rheumatology, Frontiers in Immunology
See CRP by age and sex, with the U.S. survey numbers where they exist.
Wellness targets
Narrower ranges some clinicians aim for. Being outside one doesn’t mean something is wrong.
0–0.99 mg/L (Adults). Evidence: Limited. For hs-CRP tests, the AHA/CDC 2003 statement puts under 1 mg/L in the lower relative-risk group for heart disease, and large cohort studies show risk rising steadily with CRP. But the link weakens after adjusting for usual risk factors, no trial has tested a CRP target, and the US Preventive Services Task Force (2018) found the evidence insufficient to guide care by hs-CRP.
AHA/CDC hs-CRP relative-risk groups for heart disease (2003); for hs-CRP assays in people who are not acutely ill
- Lower relative riskbelow 1 mg/L
- Average relative risk1 to under 3.01 mg/L
- Higher relative risk3.01 and above mg/L
ACC/AHA risk-enhancing factor threshold for hs-CRP (2018 cholesterol and 2019 primary prevention guidelines)
- Below 2.0 mg/Lbelow 2 mg/L
- 2.0 mg/L or higher: listed as a risk-enhancing factor, if measured2 and above mg/L
If this applies to you
CRP means a little more for some people. Open the one that fits you.
Celiac disease or IBD
CRP is a blood marker of inflammation. AGA guidance uses it alongside calprotectin and symptoms to help judge Crohn's disease activity. BSG notes that ferritin is harder to read during inflammation, and that zinc and vitamin D can only be read reliably when CRP is low.
High cholesterol or heart risk
High-sensitivity CRP (hs-CRP) picks up very small rises in CRP and is used to estimate heart risk. If it is measured, the 2026 U.S. guideline counts an hs-CRP of 2 mg/L or more on more than one occasion as a risk-enhancing factor.
Tracking for long-term health
If high-sensitivity CRP (hs-CRP) is measured, the 2026 U.S. cholesterol guideline counts a level of 2 mg/L or more on more than one occasion, with no other cause found, as a factor that adds to heart risk.
Low iron or anemia
Ferritin rises with inflammation, so a CRP measured alongside ferritin helps show whether ferritin can be taken at face value. BSG lists CRP with transferrin saturation and red cell measures as tools for this.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore CRP by age and sex: every percentile as a table, with a download.
What can affect your result
- Recent infection, illness, injury, dental work or surgery: CRP can stay raised for days to weeks
- Body weight: levels tend to be higher in people with obesity
- Sex: females often have slightly higher levels than males (in one large US study of adults aged 30 to 65, the median was 3.3 mg/L in women and 1.8 mg/L in men)
- Age and ancestry: levels tend to rise with age, and were higher in Black than in white adults in one large US study
- Smoking, gum disease, poor sleep and depression are linked with higher levels
- Pregnancy: levels run higher, especially in the third trimester (median about 4.1 mg/L in one study of 100 healthy women)
- Medicines: statins lower hs-CRP, while hormone therapy for menopause taken by mouth and birth control pills are linked with higher results
- Time of day, meals and season: none of these changes CRP in a meaningful way, so fasting isn't needed
- Test type: the standard CRP and hs-CRP assays are built for different ranges, so check which one your report shows
- Recent infection, illness, injury, dental work or surgery can raise CRP for days to weeks, so a result taken while you're unwell may not show your usual level. ARUP advises repeating an hs-CRP above 3.0 mg/L at least 2 weeks later, when you're free of infection or acute illness.
- Statin medicines lower hs-CRP, and hormone therapy for menopause taken by mouth and birth control pills are linked with higher results. Tell the person reading your result about any medicines you take.
- ARUP notes that significantly decreased CRP values may occur in specimens from patients treated with carboxypenicillins.
- Labs may reject specimens with gross hemolysis, lipemia or icterus (Mayo, Labcorp and ARUP rejection criteria differ slightly by test).
- The standard CRP assay is built for the inflammatory range and may be imprecise at low levels. Only an hs-CRP (high sensitivity or cardiac) result should be read against the heart-risk groups.
Any time of day. CRP shows no day-night pattern, and eating doesn't change it. CRP rises within hours of a trigger (above 5 mg/L by about 6 hours) and peaks around 48 hours. It falls quickly once the trigger settles, because its half-life is about 19 hours.
When to talk to a clinician
Call your clinician soon if your CRP stays above about 10 mg/L when it is repeated, or if any raised result comes with fever, a hot or swollen joint, severe or worsening pain, or feeling very unwell. If you have chest pain, trouble breathing, confusion or fainting, call 911 or your local emergency number. CRP should always be read alongside how you feel.
Questions you could ask
- Which CRP test does my lab use, and what range does it show for me?
- Do any of my medicines or supplements affect this result?
- Could a recent illness, injury, dental problem or new medicine explain this result?
- Should we repeat the test in a few weeks, when I'm feeling well?
- Was this the standard CRP or the high-sensitivity (hs-CRP) test, and does that change how you read it?
- How does this fit with my cholesterol, blood pressure and other results?
Questions people ask
What's the difference between CRP and hs-CRP?
They measure the same protein. The standard CRP test is meant for the higher levels seen with infection and inflammation, and it may not be precise at low levels. The hs-CRP test is more sensitive, which is why it is the one used in heart-risk checks. If your question is about heart health, check that your report says "high sensitivity" or "cardiac".
My hs-CRP is above 3 mg/L. What does that mean?
In the AHA/CDC grouping used with hs-CRP, above 3 mg/L is the higher relative-risk group, based on studies of large groups of people. It doesn't mean you have heart disease. Many everyday things push CRP up for a while, and levels of 3 to 10 mg/L are found in roughly one in three Americans. Labs such as ARUP suggest repeating a result above 3 mg/L at least 2 weeks later, when you're well, and using the lower of the two. Your clinician can look at it alongside your other results.
Why might my clinician want to repeat my CRP?
CRP changes fast. It can rise within hours of a cold or a minor injury, and its half-life is about 19 hours, so one result may reflect a passing illness and not your usual level. For heart-risk checking, a repeat when you're well gives a better picture of your baseline.
Can I lower my CRP?
CRP usually falls on its own once the cause, such as an infection, has passed. For steady, mildly raised levels, not smoking, a healthy weight and good sleep are linked with lower CRP, though these are links seen in studies and not promises. Some medicines also lower hs-CRP, but decisions about medicines belong with your clinician. Whether lowering CRP itself protects the heart is still being studied.
How do I convert between mg/L and mg/dL?
Multiply mg/dL by 10 to get mg/L, so 0.5 mg/dL is 5 mg/L. To go the other way, divide by 10. Check the unit on your report, because the same number in mg/dL is ten times larger than in mg/L.
Show the science and sources
Units
- 1 mg/L = 1 mg/L
- 1 mg/L = 0.1 mg/dL
- 1 mg/L = 1 µg/mL
Is a change real?
CRP naturally varies about 29.4% from test to test in the same healthy person. Between two results from the same lab, a rise of 135% or more, or a fall of 57% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
CRP is a pentraxin: five identical, non-glycosylated subunits (23,027 Da, 206 residues each) form a 115,135 Da ring that binds phosphocholine in a calcium-dependent way. Only hepatocytes make it for the circulation, mainly under IL-6 control (Pepys and Hirschfield 2003). Serum CRP passes 5 mg/L about 6 hours after a stimulus and peaks near 48 hours. The plasma half-life is about 19 hours in health and disease alike, so the circulating level tracks the synthesis rate. There is no diurnal variation, eating has no effect and there is no significant seasonal variation in baseline levels. The dynamic range is roughly 10,000-fold, from under 0.05 mg/L to over 500 mg/L. In healthy young blood donors the median is 0.8 mg/L, the 90th percentile 3.0 and the 99th 10. In NHANES III (nephelometry, general US population) the 95th percentile was 9.5 mg/L in men and 13.9 mg/L in women, rose with age and varied by race and ethnicity (Wener 2000). In 100 healthy pregnant Swedish women (hs turbidimetry), median CRP was 2.39, 2.44 and 4.12 mg/L across the three trimesters, with 95th percentiles of 9.4, 9.2 and 16.0 mg/L. Standard assays (latex immunoturbidimetry at Labcorp, immunoturbidimetry at ARUP) are tuned to the inflammatory range and are less precise at low concentrations. hs-CRP assays (immunochemiluminometric at Labcorp, immunoturbidimetric at ARUP) are validated for the low range used in cardiovascular risk assessment. It is the same analyte, but the heart-risk groups apply only to hs assays in people who are not acutely ill. The AHA/CDC statement (2003) grouped hs-CRP as under 1, 1 to 3 and over 3 mg/L (lower, average and higher relative cardiovascular risk). ARUP advises repeating a result above 3.0 mg/L at least 2 weeks later in a metabolically stable state and using the lower value. The 2018 AHA/ACC cholesterol guideline and the 2019 ACC/AHA primary prevention guideline list hs-CRP of 2.0 mg/L or higher, if measured, as a risk-enhancing factor for adults at borderline or intermediate risk. The USPSTF (2018) found adding hs-CRP to traditional risk assessment gives small improvements in discrimination and reclassification, but judged the evidence insufficient to assess benefits and harms (I statement). In the Emerging Risk Factors Collaboration (160,309 people), the coronary heart disease risk ratio per 3-fold higher CRP was 1.63 after age and sex, 1.37 after conventional risk factors and 1.23 after fibrinogen, and whether CRP is causal is unsettled. JUPITER (rosuvastatin, hazard ratio 0.56 for the primary end point) and CANTOS (canakinumab, hazard ratio 0.85 for the one dose that met the prespecified significance threshold) enrolled people with hs-CRP of 2 mg/L or higher, but neither tested a CRP target. Statins lower hs-CRP independent of their lipid effects. Baseline CRP rises with BMI and falls with weight loss, and oral contraceptives and oral (but not transdermal) postmenopausal hormone therapy are associated with higher baseline values. Liver failure impairs CRP production, and lupus and a few other conditions give a muted CRP response despite inflammation. ARUP notes that significantly decreased CRP values may occur in specimens from patients treated with carboxypenicillins.
LOINC 30522-7 (primary), 1988-5, 71426-1, 105126-7, 48421-2. Specimen: serum-or-plasma.
Sources
- C-Reactive Protein (CRP), Serum (Mayo test ID CRP), Mayo Clinic Laboratories (catalog page mirrored on testcatalog.org)
- C-Reactive Protein, High Sensitivity, Serum (Mayo test ID HSCRP), Mayo Clinic Laboratories (catalog page mirrored on testcatalog.org)
- C-Reactive Protein (ARUP test 0050180), ARUP Laboratories
- C-Reactive Protein, High Sensitivity (ARUP test 0050182), ARUP Laboratories
- C-Reactive Protein (CRP), Quantitative (test 006627), Labcorp
- C-Reactive Protein (CRP), High Sensitivity (Cardiac Risk Assessment) (test 120766), Labcorp
- Markers of Inflammation and Cardiovascular Disease: Application to Clinical and Public Health Practice: A Statement for Healthcare Professionals From the Centers for Disease Control and Prevention and the American Heart Association, Circulation (CDC and American Heart Association) (2003)
- 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol: Executive Summary, American College of Cardiology / American Heart Association (2018)
- 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease: Executive Summary, American College of Cardiology / American Heart Association (2019)
- Risk Assessment for Cardiovascular Disease With Nontraditional Risk Factors: US Preventive Services Task Force Recommendation Statement, JAMA (2018)
- C-reactive protein: a critical update, Journal of Clinical Investigation (2003)
- What does minor elevation of C-reactive protein signify?, American Journal of Medicine (2006)
- C-reactive protein concentration and risk of coronary heart disease, stroke, and mortality: an individual participant meta-analysis, The Lancet (Emerging Risk Factors Collaboration) (2010)
- Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein, New England Journal of Medicine (2008)
- Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease, New England Journal of Medicine (2017)
- The influence of age, sex, and race on the upper reference limit of serum C-reactive protein concentration, Journal of Rheumatology (2000)
- Race and gender differences in C-reactive protein levels, Journal of the American College of Cardiology (2005)
- Plasma C-Reactive Protein and Pentraxin-3 Reference Intervals During Normal Pregnancy, Frontiers in Immunology (2021)
- C-Reactive Protein (CRP) Test, MedlinePlus (National Library of Medicine)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.