Standard CRPvshs-CRP

hs-CRP and CRP are the same molecule measured with two different tools. Standard CRP answers whether you have a significant infection or inflammation right now. High-sensitivity CRP (hs-CRP) answers a quieter question: whether a low, steady level of inflammation adds to your risk of heart attack and stroke.

Is hs-CRP the same as CRP?

Yes, for the protein; no, for the test. C-reactive protein is made by the liver in response to the signalling molecule IL-6. In healthy young adults the median level is 0.8 mg/L, the 90th centile 3.0 mg/L and the 99th centile 10 mg/L, but after a strong trigger such as a bacterial infection it can rise more than 10,000-fold within hours. ¹ One assay cannot do both jobs well. Standard CRP is calibrated for the high end, where it tracks infection and inflammation. hs-CRP is calibrated for the low end, where differences of 1 or 2 mg/L matter.

The CRP marker page and the hs-CRP marker page each cover their own ranges. This page is about choosing between them and reading them together.

hs-CRP and CRP side by side

How hs-CRP is read for heart risk

The 2003 scientific statement from the American Heart Association and the US Centers for Disease Control and Prevention set the categories still used on most reports: under 1.0 mg/L lower relative risk, 1.0 to 3.0 mg/L average, and over 3.0 mg/L higher. The statement advised measuring hs-CRP twice, ideally about two weeks apart, in someone who is well, and averaging the two. ²

The 1 to 3 band reads two ways because US prevention guidance uses a different line. The 2019 ACC/AHA primary prevention guideline lists an hs-CRP of 2.0 mg/L or higher as a risk-enhancing factor, one of several things that can tip a borderline decision about cholesterol treatment. ⁴ That cut-off comes from the JUPITER trial, which enrolled people with LDL cholesterol under 130 mg/dL and hs-CRP of 2.0 mg/L or more. ⁵

In current U.S. guidelines, hsCRP carries a class IIb assessment and is most appropriate in primary prevention when clinical decisions to initiate statin therapy are uncertain.Ridker PM. A Test in Context: High-Sensitivity C-Reactive Protein. J Am Coll Cardiol, 2016 ³

In plain terms, hs-CRP is a tie-breaker. It does not replace cholesterol, blood pressure, smoking status or diabetes in a risk estimate. Read it beside your LDL cholesterol and the rest of your lipid panel.

What standard CRP is for

Standard CRP starts rising within about 6 hours of a trigger, peaks near 48 hours and falls with a half-life of about 19 hours once the trigger stops. ¹ That speed makes it useful for following an infection or recovery from surgery day by day. It responds more quickly to changes in the illness than the older sedimentation rate. ⁶ The ESR marker page covers that test.

What moves hs-CRP between tests

Because hs-CRP reads such small amounts, ordinary life shows up in it. The things that most often shift a result are listed below; most of them push it up for days, and a few hold it higher for as long as they last. ^{2 3}

• A cold, flu, dental infection, injury or recent surgery: can lift hs-CRP for days or longer, which is why the test is repeated once you are well. ²
• Very hard or long exercise in the previous day or two.
• Excess body fat and smoking: hold hs-CRP higher for as long as they persist. Diet, exercise and stopping smoking are the first steps clinicians suggest for a raised level. ³
• Flares of arthritis, gum disease or bowel inflammation.
• Statins: in the JUPITER trial, rosuvastatin lowered hs-CRP by 37% alongside a 50% fall in LDL cholesterol. ⁵ Any change to a prescribed medicine belongs with the prescriber.

When hs-CRP and CRP results seem to disagree

Because they measure the same protein, true disagreement is rare. What looks like disagreement is usually a range or units problem, or two tests taken on different days.

Standard CRP normal, hs-CRP high

This is the most common puzzle and it is not a contradiction. A standard CRP reported as under 5 mg/L can sit alongside an hs-CRP of 4 mg/L: both are true. The standard result only says there is no large inflammatory rise; the hs-CRP result places you in the higher cardiovascular risk band. ²

hs-CRP over 10 mg/L

A heart-risk test that comes back at 14 mg/L usually caught a cold, a dental infection, an injury, a flare of arthritis or a very hard training session. The result cannot be used for heart risk; the AHA/CDC statement advises finding the cause and repeating the test once you are well. ² A level that stays above 10 mg/L with no explanation is worth raising with a clinician.

Two hs-CRP results far apart

hs-CRP varies from week to week, which is why two measurements are averaged. ² One reading of 0.8 mg/L and another of 2.6 mg/L do not mean something changed; the average is the number to use.

Units that look ten times different

Some labs report CRP in mg/dL, others in mg/L. 1 mg/dL equals 10 mg/L, so a result of 0.3 mg/dL is the same as 3 mg/L. Check the unit before comparing a result with the heart-risk bands, which are always given in mg/L. ² More on this in blood-test units explained.

Which one should you ask about?

• Unwell, feverish, recovering from surgery, or monitoring an inflammatory condition: standard CRP. ¹
• Well, and weighing your heart and stroke risk with a clinician: hs-CRP, ideally twice, read alongside cholesterol and blood pressure. ^{2 3}
• Already had a standard CRP of under 5 mg/L: that result does not answer the heart-risk question.
• Recently ill or injured: wait until you are well before an hs-CRP, or the result will read high for reasons unrelated to your arteries.

hs-CRP is often read with other cardiovascular markers such as homocysteine, triglycerides and non-HDL cholesterol, and with a blood pressure check. See high cholesterol and metabolic syndrome for where it fits in those conditions, and how to read inflammation markers for the wider picture.

Standard CRP tells you whether you are inflamed today, hs-CRP tells you where a low background level sits when you are well, and an hs-CRP above 10 mg/L belongs to the first question, not the second.

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