C-Reactive Protein n.
Standard CRP tests measure acute inflammation, often in the hundreds of mg/L; hs-CRP assays read the much narrower 0.1 to 10 mg/L range used for risk stratification.
The definition
C-Reactive Protein is an acute-phase protein that the liver synthesises within hours of infection, injury, or tissue damage, driven chiefly by interleukin-6 signalling from immune cells. A high-sensitivity blood test, hs-CRP, detects the much lower chronic elevations linked to cardiovascular risk, distinct from the sharp spikes seen during active infection or trauma.
44%
fewer cardiovascular events on statin therapy in adults with elevated hs-CRP
RIDKER ET AL. · 2008 4
The mechanism
Interleukin-6 released by immune cells during infection, injury, or tissue damage is the dominant signal that drives hepatocytes to manufacture C-reactive protein, with interleukin-1beta and tumour necrosis factor alpha modulating the response but unable to reproduce it alone. 2 The finished molecule is a pentraxin, a pentameric plasma protein built from five identical subunits arranged in a ring, which binds phosphocholine exposed on damaged cell membranes and on microbial surfaces. 1 That binding activates the classical complement pathway and flags the bound material for phagocytosis, linking a liver-made protein directly into the immune system's clean-up machinery.
C-reactive protein's plasma clearance rate stays essentially constant regardless of how much is circulating, so its concentration is governed almost entirely by how fast the liver is making it. 1 That property is what makes it useful: levels can climb more than a thousandfold within 24 to 48 hours of an acute stimulus, then fall back just as quickly once the underlying insult resolves. A blood test taken during recovery from a minor injury already looks close to baseline, and a test taken during active infection looks close to its peak.
In practice
A standard lipid panel can miss cardiovascular risk that is driven by inflammation rather than cholesterol alone. Adding an hs-CRP reading to that panel changes the picture.
Worked example
Two adults share identical LDL cholesterol and blood pressure readings, so a routine lipid panel marks them as equally low-risk. An hs-CRP test then places one of them above the 2 mg/L threshold used to flag elevated inflammatory risk, while the other sits comfortably below it. The first result surfaces a risk that cholesterol numbers never revealed, and shifts the conversation towards statin therapy or anti-inflammatory lifestyle changes rather than reassurance based on lipids alone.
Cholesterol and inflammation are separate risk pathways, and hs-CRP is the test that catches the one a standard lipid panel cannot see.
Why it matters
Elevated C-reactive protein tracks cardiovascular risk closely enough to guide treatment decisions on its own, independent of cholesterol. In a pooled analysis spanning 160,309 people free of vascular disease across 54 prospective studies, log CRP concentration rose in a near-log-linear relationship with the risk of coronary heart disease, ischaemic stroke, and non-vascular death. 3
That gradient held even in adults whose LDL cholesterol already sat below 130 mg/dL, in a randomised trial that showed CRP carries risk information cholesterol alone misses. Statin therapy targeted at that residual inflammatory risk cut cardiovascular events by 44% relative to placebo, and the same trial recorded a 37% fall in hs-CRP alongside the LDL reduction, evidence that measuring and acting on inflammation, not just lipids, changes outcomes. 4 Exercise offers a non-pharmacological lever on the same pathway: structured training programmes produce a measurable fall in CRP that is not fully explained by the weight loss that often accompanies them, an anti-inflammatory effect distinct from statin therapy. 5
Questions of record
What is C-reactive protein and why does it rise so quickly after an injury or infection?
CRP is a protein your liver releases in response to interleukin-6 signals from immune cells reacting to damage or infection. Because its clearance rate barely changes, its blood level is set almost entirely by how fast the liver is producing it, which is why it can climb sharply within a day and fall just as fast once healing is underway.
Is a CRP test the same as a high-sensitivity CRP (hs-CRP) test?
No. A standard CRP test is built to detect the large spikes seen during active infection or injury, often reading in the hundreds of mg/L. An hs-CRP test uses a more sensitive assay tuned to the much lower 0.1 to 10 mg/L range, which is the range relevant to long-term cardiovascular risk rather than acute illness.
Does a high CRP mean I have heart disease?
Not on its own. A single raised hs-CRP reading is a risk signal, not a diagnosis. Large pooled data covering over 160,000 people show CRP concentration rising in step with coronary heart disease, stroke, and mortality risk, but that relationship describes probability across populations, and your own result needs interpreting alongside cholesterol, blood pressure, and other risk factors.
Can exercise or diet lower C-reactive protein?
Structured exercise training produces a measurable reduction in CRP, according to a systematic review of randomised and non-randomised controlled trials, and the effect is not fully explained by accompanying weight loss. That distinction matters: exercise appears to lower inflammation through a mechanism separate from fat loss, which is relevant to anyone whose weight has not changed much.