Lab result explainedInflammationLast updated November 1, 2026

CRP blood test: what high C-reactive protein and hs-CRP levels mean

C-reactive protein (CRP) · C-reactive protein · reported in mg/L (some US labs report mg/dL; 1 mg/dL = 10 mg/L)

C-reactive protein (CRP) is a protein your liver releases into the blood within hours of any significant inflammation, and a CRP blood test is the most widely used measure of how much inflammation is going on in your body right now. On a standard test, normal is under 10 mg/L (most healthy adults are under 3). The two most common reasons it is high are an infection, which can push it anywhere from 10 to several hundred, and a chronic inflammatory condition such as rheumatoid arthritis or inflammatory bowel disease.

There are two versions of the test. The standard CRP is used to detect and track infection and inflammatory disease. The high-sensitivity CRP (hs-CRP) measures the same protein but accurately down to 0.1 mg/L, and is used in otherwise healthy people to estimate heart disease risk: under 1 mg/L is low risk, 1 to 3 average, and over 3 mg/L high. Excess body fat, smoking, poor sleep and inactivity all keep hs-CRP in the 3 to 10 range, which is the band most readers searching for their result fall into.

CRP tells you that inflammation is present and roughly how much, but not where or why. It rises within 6 hours, peaks around 48 hours and falls with a half-life of about 19 hours once the trigger is gone, which makes it excellent for following the course of an illness or treatment. A single high value needs a reason; a value over 10 with no obvious cause is repeated after two to three weeks before anything is concluded.

CRP at a glance

  • What it is: an acute-phase protein made by the liver in response to interleukin-6; a fast, general gauge of inflammation.
  • Normal (standard CRP): under 10 mg/L; most healthy adults are under 3 mg/L. Some labs report mg/dL (divide by 10).
  • hs-CRP for heart risk: under 1 mg/L low, 1–3 average, over 3 high; above 10 is acute inflammation and should be repeated when well.
  • 10–40 mg/L suggests mild inflammation or a viral infection; 40–200 bacterial infection or active inflammatory disease; over 200 severe infection, sepsis or major tissue injury.
  • Low CRP is good; it is not a cause for concern on its own.
  • Next step: find the cause (history, exam, CBC, ESR, urine, imaging as needed), treat it, and recheck; for hs-CRP, address weight, smoking, sleep and activity, then recheck in 3 months.

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What CRP measures

When tissue is injured or infected, immune cells release interleukin-6, which tells liver cells to produce CRP. The protein binds to damaged cell membranes and to bacteria, flagging them for clearance by the complement system and phagocytes. Because production depends almost entirely on IL-6 and the liver, CRP is a remarkably faithful readout of the overall inflammatory signal in the body, rising up to a thousandfold in severe bacterial infection.

The standard assay measures CRP by immunoturbidimetry or nephelometry with a lower limit of about 3 to 8 mg/L, which is fine for infection but too coarse for the subtle, chronic elevation linked to cardiovascular risk. The high-sensitivity assay uses the same antibody chemistry with better precision at low concentrations (down to 0.1 mg/L). It is the same molecule; an hs-CRP of 2.5 mg/L and a standard CRP reported as less than 3 are describing the same thing.

CRP is not fasting-dependent and has no daily rhythm of note, but it does vary from week to week by 20 to 30 percent in healthy people, rises after vigorous exercise, surgery, vaccination and dental work, is higher in pregnancy and with oral estrogen, and is lowered by statins. For cardiovascular risk assessment, guidelines recommend two hs-CRP measurements at least two weeks apart, taken when well, and using the average.

Normal range for CRP

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

GroupTypical range (mg/L (some US labs report mg/dL; 1 mg/dL = 10 mg/L))Notes
Standard CRP, normalBelow 10 mg/L (often reported as below 3, 5 or 8 depending on the assay)Most healthy adults are under 3 mg/L. Labs differ; use the printed cut-off.
hs-CRP, low cardiovascular riskBelow 1.0 mg/LAmerican Heart Association / CDC categories, measured when well.
hs-CRP, average cardiovascular risk1.0–3.0 mg/LRoughly the middle third of the US adult population.
hs-CRP, high cardiovascular riskAbove 3.0 mg/LAssociated with about twice the risk of heart attack and stroke compared with below 1. A value of 2 mg/L or more is a risk-enhancer in the 2018 ACC/AHA cholesterol guideline.
Mild elevation10–40 mg/LViral infection, mild bacterial infection, low-grade inflammatory disease, obesity, pregnancy, recent exercise or injury. Repeat in 2 to 3 weeks if no cause.
Moderate elevation40–200 mg/LBacterial infection (pneumonia, pyelonephritis, cellulitis), active rheumatoid arthritis, Crohn's or ulcerative colitis flare, heart attack, after surgery.
Marked elevationAbove 200 mg/LSevere bacterial infection, sepsis, extensive burns, major trauma, vasculitis or severe pancreatitis. Values up to 500 mg/L occur.
Pregnancy and oral estrogenUp to about 2 to 3 times usualhs-CRP is not a reliable heart-risk marker during pregnancy or on oral contraceptives or oral HRT.

High CRP

A high CRP means your body is mounting an inflammatory response somewhere. The size of the rise narrows it down. Values between 10 and 40 mg/L are typical of viral infections, mild bacterial infections and low-grade inflammatory conditions. Values from 40 to 200 point to bacterial infection or an active inflammatory disease such as rheumatoid arthritis, inflammatory bowel disease, vasculitis or polymyalgia rheumatica. Above 200 almost always means severe bacterial infection, sepsis, major tissue damage (surgery, burns, heart attack) or a serious flare of inflammatory disease.

A CRP of 3 to 10 mg/L on an hs-CRP test in someone who feels well is a different message. It reflects chronic low-grade inflammation, most often from excess abdominal fat (fat tissue makes IL-6), smoking, sleep apnea, periodontal disease, inactivity or prediabetes. This level roughly doubles long-term cardiovascular risk compared with a value under 1 mg/L and is the signal that lifestyle levers, and sometimes a statin, are worth discussing.

CRP does not identify the source. It cannot distinguish infection from autoimmune disease or injury, and a normal CRP does not exclude illness: systemic lupus, some viral infections, early infection and many cancers produce little CRP. It is interpreted alongside your symptoms, examination, white cell count, ESR and targeted tests.

Common causes

  1. Acute infection

    Bacterial infections drive the highest values (pneumonia, kidney infection, cellulitis, abscess, bacterial meningitis), typically above 40 to 100 mg/L. Viral infections usually stay below 40, though influenza, COVID-19 and adenovirus can exceed that.

  2. Chronic inflammatory and autoimmune disease

    Rheumatoid arthritis, Crohn's disease, ulcerative colitis, psoriatic arthritis, ankylosing spondylitis, polymyalgia rheumatica, giant cell arteritis and other vasculitides raise CRP in proportion to disease activity; it is used to monitor treatment.

  3. Obesity, metabolic syndrome and insulin resistance

    Visceral fat cells secrete interleukin-6, so hs-CRP rises with waist size; people with obesity commonly run 3 to 10 mg/L. This is the most common reason for a mildly raised hs-CRP in someone who feels well.

  4. Tissue injury: surgery, trauma, burns, heart attack

    Any significant cell death triggers CRP; after major surgery it peaks at 100 to 200 mg/L around day 2 and should be falling by day 4. A persisting or second rise suggests a post-operative infection.

  5. Smoking, sleep deprivation and sleep apnea

    Smoking roughly doubles hs-CRP through airway and vascular inflammation. Short or fragmented sleep and untreated sleep apnea raise IL-6 and CRP, and CPAP lowers them.

  6. Cancer

    Lymphoma, kidney, lung, pancreatic and metastatic cancers often raise CRP to 10 to 100 mg/L, usually with other findings such as weight loss, night sweats or anemia. A persistently high CRP with no explanation is one reason imaging is sometimes ordered.

  7. Periodontal disease and other low-grade infections

    Chronic gum disease, chronic sinusitis, chronic bronchitis and a smouldering urinary infection each add a few mg/L and are easy to miss.

  8. Pregnancy, oral estrogen and recent vaccination

    Estrogen increases hepatic CRP production, so pregnancy, the combined pill and oral HRT raise it 2 to 3 fold. Vaccines produce a transient rise for a few days.

  9. Recent strenuous exercise

    A marathon or an unaccustomed hard workout causes muscle micro-injury and a CRP rise to 10 to 30 mg/L that resolves within 2 to 3 days; regular moderate exercise lowers baseline CRP.

  10. Pancreatitis, inflammatory lung disease and other organ inflammation

    Acute pancreatitis (CRP above 150 at 48 hours predicts a severe course), COPD exacerbations, pericarditis and inflammatory kidney disease all raise CRP.

Symptoms that can go with it

  • Often none when CRP is only mildly raised (hs-CRP 3 to 10 mg/L)
  • Fever, chills, sweats and feeling generally unwell with infection
  • Pain, swelling, warmth or stiffness in joints, worse in the morning, with inflammatory arthritis
  • Abdominal pain, diarrhoea with blood or mucus, with inflammatory bowel disease
  • Cough with coloured sputum, breathlessness or chest pain with pneumonia or pericarditis
  • Headache, scalp tenderness, jaw pain on chewing or visual changes in people over 50 (giant cell arteritis)
  • Unexplained weight loss, night sweats, persistent fatigue or new lumps, which need investigation

Low CRP

There is no lower limit of concern for CRP. An hs-CRP below 1 mg/L, or a standard CRP reported as undetectable, means there is little inflammation in your body and your cardiovascular risk from this factor is low. Statins, weight loss, regular exercise and not smoking all push CRP down, and a fall in CRP is one of the ways clinicians confirm an infection or an inflammatory disease is responding to treatment.

The one caution is that a normal or low CRP does not rule illness out. Systemic lupus characteristically produces a high ESR with a normal CRP unless there is serositis or infection, some viral infections and early bacterial infections have not yet raised it, and severe liver failure can impair the liver's ability to make CRP at all.

Common causes

  1. Good health and low inflammatory burden

    Lean body composition, regular activity, not smoking and good sleep keep IL-6 low and hs-CRP under 1 mg/L. This is the expected result in most healthy younger adults.

  2. Statins and some other medications

    Statins lower hs-CRP by about 15 to 40 percent independent of cholesterol, and anti-inflammatory biologics (tocilizumab in particular, which blocks IL-6) can drive CRP to zero even during active infection, which is a known pitfall.

  3. Lupus and some inflammatory diseases

    Interferon-driven diseases such as systemic lupus erythematosus suppress hepatic CRP production, so disease activity shows up as a high ESR with a disproportionately low CRP.

  4. Severe liver failure

    The liver makes CRP; in advanced cirrhosis or acute liver failure the response to infection can be blunted, so a modest CRP may still signal serious infection.

  5. Very early infection or sampling before the peak

    CRP takes 6 to 12 hours to rise and 24 to 48 hours to peak, so a test in the first hours of an illness can be normal; procalcitonin or a repeat CRP at 24 hours helps.

Symptoms that can go with it

  • None; a low CRP does not cause symptoms
  • If you feel unwell despite a normal CRP, the symptom still needs an explanation, since CRP does not detect every illness

Read it alongside

  • ESR (erythrocyte sedimentation rate) — a slower, longer-lasting inflammation marker; a high ESR with a normal CRP points to lupus, myeloma or anemia rather than infection.
  • White blood cell count and neutrophils — a high neutrophil count with a high CRP favours bacterial infection; lymphocytes favour viral.
  • Procalcitonin — rises more specifically in bacterial infection and helps decide whether antibiotics are needed when CRP is in the 20 to 100 range.
  • Ferritin — another acute-phase protein; very high ferritin with high CRP suggests adult Still's disease, hemophagocytic syndromes or severe infection.
  • LDL cholesterol, A1C and blood pressure — hs-CRP adds to, rather than replaces, these in estimating cardiovascular risk.
  • Albumin — falls as CRP rises in prolonged inflammation; the ratio tracks severity in hospital.
  • Rheumatoid factor, anti-CCP, ANA — ordered when joint symptoms accompany a persistently high CRP.
  • Fecal calprotectin — distinguishes inflammatory bowel disease from irritable bowel syndrome when CRP is borderline.

What usually happens next

  1. If you are unwell, the CRP is read with your symptoms and examination and usually a CBC, urine test and sometimes a chest X-ray or other imaging to find the source; treatment targets the cause, not the number.
  2. A CRP above 10 mg/L with no obvious cause is repeated in 2 to 3 weeks; if still raised, expect a fuller work-up (ESR, autoimmune screen, protein electrophoresis, imaging as indicated).
  3. A CRP that is falling on treatment (typically halving every 1 to 2 days once the trigger is removed) confirms the treatment is working; a rise after initial improvement suggests a new infection or complication.
  4. For an hs-CRP between 1 and 10 in someone who feels well, the useful questions are about waist size, smoking, sleep, gum health and activity, and whether a statin is appropriate given overall cardiovascular risk.
  5. For heart-risk purposes, ask for a repeat hs-CRP at least two weeks later, when you are well, and use the average of the two.

Diet, lifestyle and natural levers with evidence

What can move CRP once the cause is known. Nothing here replaces finding the cause.

Weight loss, particularly abdominal fat

Strong evidence

A meta-analysis of 33 studies found CRP fell by about 0.13 mg/L for every kilogram lost, regardless of whether the loss came from diet, exercise or surgery, so a 10 kg loss lowers hs-CRP by roughly 1.3 mg/L, enough to move many people from the high-risk to the average-risk band. The mechanism is reduced IL-6 release from visceral fat.

Stop smoking and treat sleep apnea

Strong evidence

Smokers have hs-CRP levels about 50 to 100 percent higher than non-smokers, and levels fall toward non-smoker values over the five years after quitting. Untreated obstructive sleep apnea raises CRP, and meta-analyses of CPAP trials show a reduction of around 0.5 to 1 mg/L with regular use. Both are among the largest modifiable drivers of chronic inflammation.

Regular moderate exercise

Moderate evidence

A meta-analysis of 83 randomised trials found exercise training lowered CRP by a modest but consistent amount (about 0.3 to 0.5 mg/L on average), with larger reductions when body fat also fell and in people starting with higher CRP. Aerobic and resistance training both work; 150 minutes a week of moderate activity is the dose most trials used.

A single very hard or unaccustomed session raises CRP for 2 to 3 days, so do not test straight after a race or a new programme.

Mediterranean-style eating pattern

Moderate evidence

In the PREDIMED trial, a Mediterranean diet supplemented with extra-virgin olive oil or nuts lowered CRP and IL-6 compared with a low-fat control over one to five years, and a meta-analysis of 15 trials found a mean CRP reduction of about 1 mg/L with Mediterranean diets. Higher fibre intake (over 25 g a day) is independently associated with lower CRP in observational studies, while sugar-sweetened drinks and refined grains are associated with higher levels.

Omega-3 fatty acids (EPA and DHA)

Moderate evidence

A meta-analysis of 68 randomised trials found fish-oil supplements lowered CRP, IL-6 and TNF-alpha, with the clearest effect in people with chronic inflammatory conditions and at doses of 1 to 3 g of EPA plus DHA a day for 3 months or more. The effect in healthy people with normal CRP is small or absent.

Doses above 3 g a day can increase bleeding tendency and, in some trials, atrial fibrillation; discuss if you take anticoagulants.

Curcumin

Moderate evidence

Meta-analyses of randomised trials report that curcumin (typically 500 to 2,000 mg a day of an enhanced-absorption formulation for 4 to 12 weeks) lowers CRP by around 2 mg/L in people with raised baseline inflammation such as metabolic syndrome, osteoarthritis or type 2 diabetes, with little effect in people whose CRP is already low. Plain turmeric powder is poorly absorbed; trials used piperine or lipid-based formulations.

Can increase bleeding with anticoagulants, interact with some chemotherapy and cause gallbladder contraction; rare reports of liver injury with high-dose supplements.

When to see a clinician promptly

  • A CRP above 100 mg/L, or any high CRP with fever, shaking chills, confusion, a fast heart rate or breathlessness: possible serious bacterial infection or sepsis, needs same-day assessment.
  • A CRP above 10 mg/L that stays raised on a repeat test 2 to 3 weeks later with no explanation, particularly with weight loss, night sweats, persistent fatigue or new pain.
  • High CRP with new headache, scalp tenderness or visual disturbance in anyone over 50: giant cell arteritis can cause permanent sight loss and is treated urgently.
  • High CRP with chest pain, or with a hot swollen joint, severe abdominal pain or bloody diarrhoea.
  • A rising CRP after surgery or during treatment of an infection, which suggests a complication.
  • hs-CRP persistently above 3 mg/L with other cardiovascular risk factors (high LDL, high blood pressure, diabetes, family history), to discuss statin treatment and risk reduction.

Frequently asked questions

What is a normal CRP level?

On a standard test, under 10 mg/L is considered normal and most healthy adults are under 3 mg/L; many labs simply report values below their detection limit (3, 5 or 8 mg/L) as normal. On the high-sensitivity test used for heart risk, under 1 mg/L is low risk, 1 to 3 average and over 3 high. If your lab reports mg/dL, multiply by 10 to compare.

Is a CRP of 10, 20 or 50 high?

A CRP of 10 mg/L is the threshold for clinically significant inflammation; 10 to 20 is a mild rise typical of a viral infection, minor injury, obesity or low-grade inflammatory disease. A CRP of 50 is a moderate rise more typical of a bacterial infection or an active flare of inflammatory disease and usually needs a cause identified. In each case the trend and your symptoms matter more than the single value.

What is the difference between CRP and hs-CRP?

They measure the same protein. The standard CRP test is accurate from about 3 to 8 mg/L upward and is used for infection and inflammatory disease. The high-sensitivity (hs-CRP) test is accurate down to 0.1 mg/L and is used in people who feel well to grade chronic low-level inflammation for cardiovascular risk. An hs-CRP above 10 is simply acute inflammation and should be repeated when you are well.

Can CRP tell if an infection is bacterial or viral?

Only roughly. Values above 100 mg/L strongly favour bacterial infection and values below 20 favour viral, but there is a large overlap between 20 and 100 where CRP alone cannot decide. Procalcitonin, the white cell differential and the clinical picture are used together. Some viral infections, including influenza and COVID-19, can push CRP well above 50.

Can stress or anxiety raise CRP?

Chronic psychological stress, depression and poor sleep are associated with modestly higher hs-CRP (often 1 to 2 mg/L higher) in population studies, through sustained cortisol disruption and IL-6 release, and treating depression or improving sleep lowers it slightly. Stress does not produce the 10, 50 or 100 mg/L values seen with infection and inflammatory disease; those need another explanation.

What cancers cause high CRP?

Lymphoma, kidney cancer, lung cancer, pancreatic cancer, ovarian cancer and metastatic cancer of any type can raise CRP, usually to between 10 and 100 mg/L, through tumour-related IL-6 and tissue breakdown. CRP is not a cancer screening test; the vast majority of raised CRPs are infection, inflammatory disease or obesity. Cancer becomes a consideration when CRP stays high with no cause and there is weight loss, night sweats, anemia or a lump.

How quickly does CRP come down?

CRP has a half-life of about 19 hours, so once the cause is treated it roughly halves every day or two: a CRP of 160 from pneumonia typically falls below 40 within four to five days of effective antibiotics. If it is not falling by day three to four, the treatment or the diagnosis is reviewed. Lifestyle-driven hs-CRP changes are slower, taking weeks to months of weight loss or exercise to show.

Do I need to fast for a CRP test?

No. CRP is not affected by food. It is often drawn together with a lipid panel or glucose, which may require fasting, but the CRP itself can be taken at any time. Avoid testing hs-CRP for heart risk within two weeks of an infection, injury, vaccination or an unusually hard workout, and mention oral contraceptives, HRT, statins or pregnancy, all of which shift the value.

References

  1. C-reactive protein (CRP) test. MedlinePlus, US National Library of Medicine (2023)View source
  2. C-reactive protein test. Mayo Clinic (2022)View source
  3. Pearson TA, Mensah GA, Alexander RW, et al.. 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 (2003)
  4. Pepys MB, Hirschfield GM. C-reactive protein: a critical update. Journal of Clinical Investigation (2003)
  5. Ridker PM, Danielson E, Fonseca FA, et al.. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein (JUPITER). New England Journal of Medicine (2008)
  6. Grundy SM, Stone NJ, Bailey AL, et al.. 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA guideline on the management of blood cholesterol. Circulation (2019)
  7. Selvin E, Paynter NP, Erlinger TP. The effect of weight loss on C-reactive protein: a systematic review. Archives of Internal Medicine (2007)
  8. Fedewa MV, Hathaway ED, Ward-Ritacco CL. Effect of exercise training on C reactive protein: a systematic review and meta-analysis of randomised and non-randomised controlled trials. British Journal of Sports Medicine (2017)
  9. Li K, Huang T, Zheng J, Wu K, Li D. Effect of marine-derived n-3 polyunsaturated fatty acids on C-reactive protein, interleukin 6 and tumor necrosis factor α: a meta-analysis. PLoS ONE (2014)
  10. Sahebkar A. Are curcuminoids effective C-reactive protein-lowering agents in clinical practice? Evidence from a meta-analysis. Phytotherapy Research (2014)
  11. Estruch R. Mediterranean diet and inflammatory response in cardiovascular disease prevention: the PREDIMED trial. Proceedings of the Nutrition Society (2010)
  12. Inflammation markers (C-reactive protein, erythrocyte sedimentation rate). Merck Manual Professional Version (2024)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.