C-Reactive Protein (CRP)

What is C-Reactive Protein (CRP)?

C-reactive protein (CRP) is a protein your liver releases into the bloodstream in response to inflammation. Its production is driven largely by the signalling molecule interleukin-6 (IL-6), so CRP starts to rise within hours of an infection, injury, or flare of an inflammatory condition, peaks after about a day or two, and falls again as the body recovers. It is a general, non-specific marker: a raised CRP tells you inflammation is present somewhere, not where it is or what is causing it. There are two ways to measure it. The standard CRP assay detects and follows infection and active inflammation; values are reported in mg/L. The high-sensitivity assay (hs-CRP) is calibrated to read accurately into the very low range and is the version used to assess long-term cardiovascular risk. The Optimize Baseline reports CRP down to a floor of <1 mg/L — values beneath that come back as a single bucket rather than an exact number. Because CRP is non-specific, it is always read alongside your symptoms and other markers, never on its own.

Why is C-Reactive Protein (CRP) relevant?

CRP has two clinically useful faces. Acutely, it is a fast, sensitive flag for infection and active inflammation. Over the long term, it is one of the best-studied markers of chronic low-grade inflammation — the slow, smouldering kind that is linked, in large studies, to atherosclerosis, insulin resistance, and metabolic syndrome, and that rarely produces obvious symptoms. For cardiovascular risk, hs-CRP is commonly grouped into broad bands (in the absence of an acute infection): below 1 mg/L is considered low risk, 1–3 mg/L average, and above 3 mg/L higher risk. These are general reference points used to refine risk, not diagnoses, and they are most informative read together with ApoB, your lipid panel, and metabolic markers like fasting glucose and HbA1c — inflammation tends to amplify the risk those markers carry. Reference ranges vary between laboratories. A markedly high CRP — for example above 10 mg/L, and often 50–100 mg/L or more — usually points to an acute infection or tissue injury rather than the slow-burn inflammation you track for prevention; values that high are set aside for cardiovascular risk scoring and prompt a look for an acute cause instead.

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

A single reading is only a snapshot. A cold, a recent hard workout, a minor injury, a dental problem, or any passing illness can push CRP up temporarily — that is not chronic inflammation. For a trustworthy baseline, measure CRP at least twice, around two weeks or more apart, when you are free of infection; if one reading is markedly high (for example above 10 mg/L), it is usually set aside and the test repeated once you have recovered. A persistently elevated CRP can have many drivers: ongoing infection, recent injury or surgery, autoimmune or inflammatory conditions (such as rheumatoid arthritis or inflammatory bowel disease), excess body fat, smoking, poor metabolic health, and — often substantially — oestrogen-containing medication such as the combined pill, as well as pregnancy. When CRP stays up without an obvious acute cause — especially alongside high ApoB, unfavourable lipids, or raised glucose — it deserves attention and a conversation with a clinician. A low result is generally reassuring: it points to a low inflammatory load. A value below the detection floor (reported as <1 mg/L) is a good sign; for precise risk stratification within that low band, a dedicated hs-CRP test is the right tool. Where chronic low-grade inflammation is the issue, the levers that tend to bring CRP down are the familiar ones: losing excess weight, moving regularly, an anti-inflammatory Mediterranean-style diet, not smoking, and good sleep — alongside treating whatever metabolic or medical driver sits underneath. Persistent elevation should always be worked up with a healthcare professional.

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