hs-CRP (high-sensitivity C-reactive protein) test: what it measures, normal levels, and what high levels say about heart risk

C-reactive protein is made by the liver in response to inflammatory signals (chiefly interleukin-6) and rises within hours of infection, injury or a flare of inflammatory disease — the 'standard' CRP test tracks those large changes, from about 10 mg/L up into the hundreds. The high-sensitivity version uses an assay precise enough to measure the much lower levels, roughly 0.1–10 mg/L, that healthy people carry all the time. In that range CRP reflects the slow, low-grade inflammation of the arterial wall and of metabolic disease, which is why it predicts future heart attacks and strokes independently of cholesterol. The two tests measure the same protein; they differ in the range they are built to read.

hs-CRP is a risk marker, not a diagnostic test. It does not show where inflammation is, and it adds to — rather than replaces — the lipid panel, blood pressure, blood sugar, smoking status and family history that make up cardiovascular risk. Its practical role is to refine the decision in people at intermediate risk, and to track the inflammatory component of metabolic health over time.

The American Heart Association and CDC categories, used by most laboratories, are: below 1.0 mg/L — lower relative cardiovascular risk; 1.0–3.0 mg/L — average risk; above 3.0 mg/L — higher risk. A value above 10 mg/L is outside the risk-marker range altogether and is read as a sign of acute inflammation or infection; it is discarded for risk purposes and the test repeated after at least two weeks. Because CRP varies day to day, the recommended approach is to average two measurements taken two or more weeks apart, both when you are well.

Median values in healthy adults sit around 1–2 mg/L and rise with age, body weight and smoking; women on oral estrogen run higher. There is no 'too low' — a value of 0.2 mg/L is simply low inflammation. Some laboratories report in mg/dL (divide mg/L by 10), so check the unit before comparing with the categories above.

Anything inflammatory, which is why timing is everything. From most to least common in people checking the test for heart risk:

Large studies have shown that people with higher hs-CRP have more heart attacks and strokes at any cholesterol level, and that lowering both LDL and CRP produces fewer events than lowering LDL alone. In practice hs-CRP is one of the 'risk-enhancing factors' in the 2018 cholesterol guideline: when a person's 10-year risk from the standard calculator is borderline or intermediate, a persistently elevated hs-CRP (2 mg/L or more in that guideline) tips the decision toward starting a statin, and the JUPITER trial showed statin benefit in people with normal LDL but hs-CRP above 2 mg/L. It is not used to screen the whole population, and it does not change management in someone already at clearly high or clearly low risk.

Read alongside the lipid panel, apolipoprotein B, lipoprotein(a) and hemoglobin A1c, hs-CRP completes a picture of plaque drivers (cholesterol particles), inherited risk (Lp(a)), metabolic risk (A1c) and inflammation. It is also a useful progress marker for lifestyle change: weight loss, exercise, better sleep, quitting smoking and treating sleep apnea all lower it, usually within months.

Standard CRP and hs-CRP measure the same protein with different sensitivity: order standard CRP to detect and follow infection or an inflammatory flare (where values run 10–300 mg/L), and hs-CRP for cardiovascular risk (0.1–10 mg/L). Many laboratories now run a single assay that covers both ranges and report it as CRP in mg/L; the name on the requisition matters less than knowing which question you are asking. ESR (erythrocyte sedimentation rate) is an older, indirect marker that rises and falls over days to weeks rather than hours, is affected by anemia, age, sex and pregnancy, and is still used for conditions such as giant cell arteritis and polymyalgia rheumatica. For heart-risk purposes ESR adds nothing to hs-CRP.

Ask whether anything inflammatory was going on within the two weeks before the draw — a cold, a vaccine, a dental procedure, a hard race — and if so, repeat the test in two to four weeks when fully well; a value above 10 mg/L should always be repeated before it is read as risk. If the repeat confirms a level above 3 mg/L (or above 2 mg/L in the guideline's risk-enhancer sense), the result belongs in a conversation with a clinician about overall cardiovascular risk: the lipid panel, blood pressure, A1c, smoking, family history and sometimes a coronary calcium score. The actions that lower hs-CRP are the ones that lower risk anyway — weight loss, regular exercise, sleep, not smoking, treating gum disease and sleep apnea — and a statin lowers it as well. A persistently high level with no cardiovascular explanation and no obvious inflammation is worth a general evaluation, because CRP is also raised by chronic infection, inflammatory disease and, rarely, malignancy.

hs-CRP is a routine chemistry test at Quest and Labcorp, available through a clinician or directly through TestWell with physician review; results post in a few business days. No fasting is needed. For a risk reading, test when you have been well for at least two weeks, avoid intense exercise for 48 hours beforehand, note any vaccine in the previous two weeks, and plan a second measurement two or more weeks later to average. It pairs naturally with a lipid panel, apolipoprotein B and lipoprotein(a) in a single draw — the heart-health panels on TestWell group them for that reason.