High CRP: what your level means, what causes it and when it matters

C-reactive protein (CRP) is a protein your liver releases into the blood when the immune system signals inflammation, and labs measure it on two very different scales. A result of 4 mg/L and a result of 140 mg/L are both flagged "high", yet the first is a slow heart-risk signal in someone who feels fine and the second usually means a serious infection. The size of the number, the test it came from and whether it stays up on a second draw decide which story your result is telling.

What counts as high CRP?

For heart-risk testing, the American Heart Association and CDC set three hs-CRP bands: below 1 mg/L is lower risk, 1 to 3 mg/L is average risk and above 3 mg/L is higher risk ¹. The same statement says a value above 10 mg/L should be repeated and a source of infection or inflammation looked for, because a number that high is no longer reading background heart risk ¹. The 2018 AHA/ACC cholesterol guideline draws its own line lower: an hs-CRP of 2.0 mg/L or more is listed as a risk-enhancing factor, one of the extras that can tip the decision toward a statin in adults at borderline or intermediate 10-year risk ². That 2 to 3 mg/L stretch is where the two documents read the same result differently.

Standard CRP results run on a wider scale, and most labs flag anything above 5 or 10 mg/L as high. Some US labs report CRP in mg/dL instead of mg/L; divide a mg/L value by 10 to get mg/dL, so 30 mg/L is 3 mg/dL. Check the unit before comparing a result with any table, because a "3" in mg/dL is ten times a "3" in mg/L. More on that in lab units explained. The table below joins both scales.

The parent page on C-reactive protein covers what the protein does and how the test is run. This page covers what to do with a result above the line.

CRP or hs-CRP: which one is on your report?

Both tests measure the same protein; hs-CRP is the high-sensitivity version, tuned to read the small amounts that matter for heart risk. The quickest tell is on the report itself: if it says "high sensitivity" or "cardio CRP", or the reference range sits around 1 to 3 mg/L, you have hs-CRP. A standard test often reports anything low as "below 5" or "below 3". The full side-by-side is on hs-CRP vs CRP.

Why CRP goes up fast and comes down fast

When tissue is infected or damaged, immune cells release a messenger called interleukin-6 (IL-6), and the liver answers by making CRP. CRP starts to climb within about 6 hours of the trigger and peaks around 48 hours ³. Your body clears half of it about every 19 hours, in health and illness alike, so once the trigger stops the level roughly halves each day ³.

The sole determinant of circulating CRP concentration is the synthesis rate.Mark Pepys and Gideon Hirschfield, Journal of Clinical Investigation, 2003 ³

Two things follow from that timing. A CRP drawn on the first morning of a fever can still look modest, and a CRP that is still rising three or four days into treatment means the cause is not under control. A CRP that falls steadily is the usual sign of recovery, even before a person feels fully well.

Common causes of high CRP

Short-lived causes

• Infections. Bacterial infections push CRP highest, often above 100 mg/L; viral infections such as colds and flu usually raise it far less ³.
• Injury, burns and surgery, including a joint replacement. CRP climbs after an operation, peaks over the next two to three days and then falls; a rise after that point is a warning sign.
• Hard or very long exercise. A marathon or a brutal training session can lift CRP for a day or more.
• Vaccines and dental work. Both can nudge CRP up for a few days.
• A recent illness you have forgotten. A cold two weeks ago is one of the most common reasons for a surprise hs-CRP of 5.

Ongoing causes

• Excess body fat, especially around the waist. Fat tissue releases IL-6, which keeps the liver making CRP.
• Insulin resistance and metabolic syndrome, which often travel with a steady hs-CRP of 3 to 10 mg/L.
• Smoking, short or broken sleep, long-running stress and untreated sleep apnoea.
• Gum disease, a long-running infection that is easy to overlook.
• Inflammatory and autoimmune disease: rheumatoid arthritis, inflammatory bowel disease and vasculitis can push CRP well above 10 during flares.
• Chronic kidney disease, where CRP is often mildly raised.

Medicines and life stages

Oral estrogen, in hormone therapy or the combined pill, commonly raises CRP through its direct effect on the liver, so a woman on oral HRT can have a higher hs-CRP without any more inflammation; this matters around menopause, when HRT often starts. Pregnancy commonly raises CRP too, especially late on. Statins lower CRP as well as LDL: in the JUPITER trial, rosuvastatin cut hs-CRP by 37% ⁸.

High CRP and your heart

An hs-CRP result is a heart-risk reading only when you are well. Guidelines use two draws at least two weeks apart, taken free of infection and averaged; fasting is not required ¹. The US guideline weighs an hs-CRP of 2 mg/L or more alongside LDL, blood pressure and family history ².

CRP tracks the inflammation that drives artery disease but does not damage arteries itself. People born with gene variants that keep their CRP high all their lives do not get more coronary heart disease ⁴. So CRP is a signal from the process, not the cause, which is why a high hs-CRP sends you to the particles that build plaque, ApoB and Lp(a) (see ApoB vs LDL and high Lp(a)). It is also why the 2021 European Society of Cardiology prevention guideline does not recommend routine biomarker tests such as hs-CRP to refine risk ⁷.

The inflammation itself still matters. In JUPITER, people with LDL below 130 mg/dL but hs-CRP of 2 mg/L or more who took rosuvastatin had 44% fewer heart attacks, strokes and related events ⁸. In CANTOS, canakinumab, an anti-inflammatory drug that does not lower cholesterol, cut repeat heart events by about 15% in people who had already had a heart attack and still had an hs-CRP of 2 mg/L or more ⁹. And over 30 years in the Women's Health Study, hs-CRP, LDL and Lp(a) each predicted heart events on their own, with the highest risk in women raised on all three ¹⁰. The wider panel is on cardiac markers explained.

When is a CRP level dangerous?

How dangerous a high CRP is depends on what is raising it and how you feel, more than on the number alone. UK doctors use the number for one everyday decision: when it is unclear whether a chest infection needs antibiotics, NICE advises no routine antibiotics below 20 mg/L, a back-up prescription between 20 and 100 mg/L, and immediate antibiotics above 100 mg/L ⁶. Those cut-offs show how clinicians weigh the size of the result against the patient in front of them.

A standard CRP that stays above 10 mg/L on repeat testing, in someone with no infection or injury to explain it, needs a clinician to look for a cause: a hidden infection, an inflammatory disease or, less often, a cancer. That workup is usually planned over days to weeks, with a physical exam and the markers below.

High CRP but you feel fine

A steady hs-CRP of 2 to 10 mg/L in someone who feels well is common. The usual drivers are excess weight, insulin resistance, smoking, short sleep and gum disease, and a forgotten cold explains many single readings. Less often the cause is a quiet infection or an early inflammatory condition, which is why a result above 10 mg/L is repeated before anyone reads it as heart risk ¹. For a result of 3 to 10 mg/L in someone who feels well, the usual next step is a repeat test about two weeks later, and a clinician may add ApoB, Lp(a) and A1C to the same draw.

High CRP rarely means cancer. Some cancers do raise CRP, but infections, injuries and metabolic causes are far more common, and a raised CRP cannot point to cancer or rule it out. A clinician looks for cancer when the CRP stays high with no other cause, or when it comes with weight loss you cannot explain, night sweats or a new lump.

Read CRP with the markers beside it

CRP tells you that something is inflamed. The markers next to it on the same report usually tell you what. A high white count with high neutrophils favours a bacterial infection (see high WBC and high neutrophils). ESR rises and falls more slowly; CRP vs ESR covers when each one helps. Ferritin also rises with inflammation, so a "normal" ferritin next to a high CRP can hide low iron stores (see iron studies explained). Albumin falls when inflammation runs for weeks, and for a steady, raised hs-CRP, A1C and fasting insulin check the metabolic driver. The wider picture is on how to read inflammation markers.

CalculatorHOMA-IR calculatorHave a fasting glucose and fasting insulin from the same draw? HOMA-IR turns them into one insulin-resistance number, the most common driver of a steady hs-CRP of 3 to 10.Work it out

How to bring a high CRP down

Treating the cause is what lowers CRP: an infection clears, a flare is controlled, a wound heals, and CRP follows within days. For a steady, raised hs-CRP, the changes with evidence behind them are mostly lifestyle ones.

• Weight loss. Across pooled studies, CRP fell by about 0.13 mg/L for each kilogram lost, so losing 10 kg tends to take about 1.3 mg/L off ⁵.
• Regular exercise. One very hard session raises CRP for a day or two, while steady training over months lowers the resting level.
• Stopping smoking, and getting checked for sleep apnoea if you snore and wake unrefreshed.
• Gum care: brushing, flossing and treating gum disease.
• A Mediterranean-style pattern of eating, heavy on vegetables, legumes, fish and olive oil.
• Statins, if a clinician prescribes one for heart risk, lower CRP as well as LDL ⁸.

Medicines and supplements studied for CRP

Strongest evidenceStatinsPrescription medicines that lower CRP alongside LDL; the US guideline counts an hs-CRP of 2 mg/L or more as one factor a clinician weighs when deciding whether one is appropriate

Mixed evidenceOmega-3 (fish oil)Trials show small, inconsistent drops in CRP, larger in people who start high; can add to the effect of blood thinnersIn our shop

Mixed evidenceTurmeric (curcumin)Meta-analyses of small trials report modest CRP reductions; product quality varies a lot; can add to the effect of blood thinnersIn our shop

A CRP above 10 mg/L usually has a cause a clinician needs to find, and a supplement will not treat it.

When to retest CRP

1. 1After an infection or injuryWait until you have felt well for one to three weeks; earlier, the result still reflects the illness.
2. 2For heart riskTwo hs-CRP draws at least two weeks apart, while well, averaged; fasting is not needed ¹. Skipping hard exercise for a couple of days beforehand avoids a false bump.
3. 3After a lifestyle changeRetest after 8 to 12 weeks, at the same lab and with the same test, so the numbers are comparable.
4. 4If CRP was above 10 mg/L with no clear causeRepeat it soon, as your clinician advises, and look for a source of infection or inflammation ¹.

A trend across two or three results says far more than any single CRP. More on CRP across the inflammation topic is on inflammation.

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