Optimize
← All biomarkers
InflammationHeart & Vascular

C-Reactive Protein (CRP)

CRP is a protein your liver makes in response to inflammation, serving as a broad marker of inflammation in your body.

What is C-Reactive Protein (CRP)?

CRP is a protein the liver releases into the bloodstream in response to inflammation. It starts rising within hours of an infection, injury, or inflammatory flare, peaks after a day or two, and falls again as the body recovers. It is a broad, non-specific marker: a raised CRP tells you inflammation is present somewhere, not where or why. Two variants exist. The standard CRP test tracks infection and active inflammation. The high-sensitivity version (hs-CRP) is calibrated for the low range and is used to assess chronic low-grade inflammation and cardiovascular risk. Always read CRP alongside symptoms and other markers — never in isolation.

Why is C-Reactive Protein (CRP) relevant?

CRP has two useful roles. Acutely, it is a fast flag for infection or active inflammation. Over the long term, it is one of the best-studied markers of chronic low-grade inflammation — the slow-burning kind linked to atherosclerosis, insulin resistance, and elevated cardiovascular risk, which rarely causes obvious symptoms. A low CRP in the absence of infection is reassuring. A persistently elevated value — especially alongside high ApoB, unfavourable lipids, or raised glucose — deserves attention. Oestrogen-containing medications such as the combined pill can substantially raise CRP; factor that in when interpreting the result.

C-Reactive Protein (CRP) high or low — what it means

A single reading is a snapshot. A cold, a recent hard workout, a minor injury, or a dental problem can temporarily push CRP up — that is not chronic inflammation. Measure CRP at least twice, at least two weeks apart, when you are free of infection. If one reading is markedly elevated, repeat it after recovery. A persistently elevated CRP without an obvious acute cause is worth investigating: excess body weight, smoking, an unfavourable metabolic profile, certain medications, pregnancy, and autoimmune conditions are common drivers. The levers for reducing low-grade inflammation are well known: losing excess weight, moving regularly, a Mediterranean-style diet, not smoking, and good sleep.

C-Reactive Protein (CRP) reference ranges

Normal (standard CRP)Upper limit is lab-dependent; some labs use a lower cut-off.< 10 mg/L
hs-CRP — low heart riskAssessed in the absence of active infection.< 1 mg/L
hs-CRP — average heart risk1–3 mg/L
hs-CRP — higher heart risk> 3 mg/L
Markedly raised (acute)Often 50–100 mg/L or more; points to acute infection or tissue injury, not the low-grade inflammation you track for prevention.> 10 mg/L

Cut-offs vary between labs and methods. The Optimize Baseline reports CRP down to a floor of <1 mg/L. The hs-CRP bands apply only in the absence of an acute infection and are reference points to refine risk, not a diagnosis.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Heart health →

Frequently asked questions

What is a normal CRP level?

On the standard CRP assay a result below about 10 mg/L is considered normal, though the exact upper limit is lab-dependent and some labs use a lower cut-off. For the high-sensitivity version (hs-CRP), used to assess heart risk, below 1 mg/L is low risk, 1–3 mg/L average, and above 3 mg/L higher risk. The Optimize Baseline reports values under 1 mg/L as a single bucket (<1 mg/L) rather than an exact number.

What does a high CRP mean?

A raised CRP means inflammation is present somewhere — not where or why. A markedly high value (above 10 mg/L, often 50–100 mg/L or more) usually points to an acute infection, injury, or surgery. A mildly raised value of 1–3 mg/L or higher without an acute cause can reflect chronic low-grade inflammation, which is linked to atherosclerosis, insulin resistance, and elevated heart risk — especially alongside high ApoB, unfavourable lipids, or raised glucose.

What does a low CRP level mean?

A low CRP in the absence of infection is reassuring: it suggests there is no active or low-grade inflammation at that moment. With CRP there is no lower limit to worry about — the lower, the better. The Optimize Baseline reports everything under 1 mg/L as a single bucket (<1 mg/L) rather than an exact number.

When is a raised CRP something to worry about?

A single reading is a snapshot: a cold, hard workout, minor injury, or dental problem can push CRP up temporarily. A value above 10 mg/L is usually set aside and repeated after recovery. More concerning is a CRP that stays persistently raised without an obvious acute cause — especially alongside other unfavourable heart or metabolic markers. That deserves further investigation and a conversation with a clinician.

How do I lower a raised CRP?

Where chronic low-grade inflammation is the cause, the familiar lifestyle levers help: losing excess weight, moving regularly, an anti-inflammatory Mediterranean-style diet, not smoking, and good sleep — alongside treating the underlying metabolic or medical driver. Bear in mind that oestrogen-containing medication such as the combined pill and pregnancy can substantially raise CRP. Ideally measure twice, around two weeks apart, when you are free of infection.

Related biomarkers

Ferritin
Ferritin is the protein that stores iron in your cells, making it the most reliable blood test for your iron stores.
Platelets
Platelets are the smallest cell fragments in your blood that clump together at a wound to stop bleeding.
Apolipoprotein B (ApoB)
ApoB is a protein on every harmful cholesterol particle, so it counts how many of those particles circulate in your blood.
HDL Cholesterol
HDL is the 'good' cholesterol that carries excess cholesterol back to your liver.
Homocysteine
Homocysteine is an amino acid your body clears with B-vitamins, rising when folate or B12 runs short.
LDL / HDL Ratio
The LDL/HDL ratio divides your 'bad' LDL cholesterol by your 'good' HDL to summarise the balance in your lipid profile.

C-Reactive Protein (CRP) is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

See the full test