hs-CRP test: what the result means (hs-CRB)

C-reactive protein (CRP) is a protein that the liver produces in response to inflammation in the body. When tissue is damaged, an infection begins or a chronic inflammatory process develops, the amount of CRP in the blood can rise within a few hours or days. The “high-sensitivity” (hs) label does not mean a different protein but a more sensitive laboratory method, one that can accurately measure small CRP values — the kind seen in chronic, low-grade inflammation rather than in an acute infection. For this reason the hs-CRP method is used more often when the aim is to follow long-term, low-grade inflammation, while the ordinary CRP test is used when an acute infection or active inflammation with considerably higher values is suspected. CRP by itself does not show where in the body the inflammation is — it only shows that an inflammatory process is present, so the result is always assessed together with symptoms and other tests.

• Fever, chills, a faster heartbeat or faster breathing, nausea or vomiting — when a bacterial or viral infection is suspected
• To monitor chronic inflammatory conditions — for example inflammatory bowel disease (Crohn's disease, ulcerative colitis) or autoimmune conditions (lupus, rheumatoid arthritis, vasculitis)
• When a lung condition such as asthma is suspected, or to assess how active the inflammation is
• After surgery — to watch for a developing infection
• When sepsis is suspected, or to assess how well treatment is working in chronic inflammation

A raised CRP shows that inflammation is going on in the body, but it does not show where it is or what is causing it. Possible causes include a bacterial or viral infection, chronic inflammatory bowel disease or autoimmune disease, and lung disease, as well as obesity, smoking or hormone therapy. The result needs to be discussed with a doctor together with symptoms and other tests.

Possible causes

• A bacterial or viral infection
• Inflammatory bowel disease (Crohn's disease, ulcerative colitis)
• Autoimmune diseases (lupus, rheumatoid arthritis, vasculitis)
• Lung diseases such as asthma
• Smoking and exposure to environmental toxins
• Insomnia, depression, hormone therapy during menopause, obesity
• Female sex — according to the source, women naturally have slightly higher values than men

Possible symptoms

• Fever
• Chills
• A faster heartbeat
• Faster breathing
• Nausea and vomiting

• Whether there are signs of an acute infection that would need treating in their own right
• Other inflammation markers assessed alongside — for example the erythrocyte sedimentation rate (ESR)
• Whether there is a known chronic inflammatory or autoimmune disease whose course may have changed
• Lifestyle factors — smoking, body weight, sleep — as possible reasons for the raised value
• When to repeat the test so that the change over time can be seen

hs-CRP below 1 mg/l — lower cardiovascular risk (AHA/MedlinePlus)

According to MedlinePlus, citing the American Heart Association, an hs-CRP value below 1 mg/l falls into the lower cardiovascular risk category. This is a statistical classification used together with other risk factors — it does not mean that there is no cardiovascular risk at all. The threshold was set in population studies in which a lower level of chronic, low-grade inflammation in the blood is linked with less frequent cardiovascular events in certain groups — a statistical association, not a diagnosis or a guarantee for an individual person.

The hs-CRP test is usually not done on its own but together with other markers — a lipid panel (total cholesterol, LDL, HDL, triglycerides), glucose or blood pressure. That is because cardiovascular risk is assessed from a combination of several factors rather than from a single number. The doctor also takes into account age, sex, smoking, family history and other illnesses. And because CRP can rise temporarily for entirely unrelated reasons — a minor infection, a recent injury or even dental treatment — one low result confirms only the situation at that moment. If the value matters for a long-term decision about risk, the doctor may recommend repeating the test after a few weeks.

• Whether a lipid panel (cholesterol, LDL, HDL, triglycerides) has been assessed alongside
• Whether other cardiovascular risk factors are known — blood pressure, glucose level, smoking, family history
• Whether there was an acute infection or injury before the test that could have temporarily affected the result
• When, if at all, it would be worth repeating the hs-CRP test for long-term monitoring

hs-CRP 1–3 mg/l — moderate cardiovascular risk (AHA/MedlinePlus)

According to MedlinePlus, citing the American Heart Association, an hs-CRP value from 1 to 3 mg/l falls into the moderate cardiovascular risk category. It is one of several factors that are assessed, not a risk measure that stands on its own, so it is combined with other tests and health data. In the AHA classification cited by MedlinePlus, the 1–3 mg/l range marks the moderate cardiovascular risk group — between the lowest and the highest categories. Such a value indicates a slightly higher level of chronic, low-grade inflammation in the blood than in the lowest risk group, but by itself it does not point to a specific disease or to how it is progressing.

Because this category sits in the middle of the range, for a doctor it often becomes a reason to look at the overall risk picture in a wider context — the lipid panel, blood pressure, glucose level, body mass index and lifestyle factors such as smoking or physical activity are all considered alongside. Together, these factors influence overall risk more than a single hs-CRP result does. It is worth remembering that hs-CRP is not specific to the cardiovascular system — any chronic inflammatory process, obesity or even a recent infection can raise it. That is why a one-off result in this range is most often assessed together with a repeat test or other data, rather than as a conclusion in itself.

• Whether the overall risk picture (lipids, blood pressure, glucose, body mass index) matches this category
• Whether there was a recent infection or inflammatory process that could have temporarily affected the result
• Lifestyle factors — smoking, physical activity, diet — as possible sources of chronic inflammation
• Whether it makes sense to repeat the hs-CRP test after some time to confirm the trend

hs-CRP above 3 mg/l — higher cardiovascular risk (AHA/MedlinePlus)

According to MedlinePlus, citing the American Heart Association, an hs-CRP value above 3 mg/l falls into the higher cardiovascular risk category. Before that, it is assessed whether the result was affected by an infection or other acute inflammation — only then is the value discussed as an indicator of long-term risk, together with other tests. In the AHA classification cited by MedlinePlus, hs-CRP above 3 mg/l marks the higher cardiovascular risk group. Two different situations do need to be told apart, though: an acutely raised CRP caused by infection, injury or a recent illness, and a stably raised marker of chronic, low-grade inflammation, which is the one linked with this risk category. A single high result, without a repeat check, does not distinguish between these two situations.

That is why, when an hs-CRP result exceeds 3 mg/l, doctors often recommend repeating the test a few weeks later, once they are sure that there was no acute infection, fever or recent surgery at the time. All of these can raise CRP temporarily and have nothing to do with long-term cardiovascular risk. As in the other categories, this value is always assessed together with the rest of the set of risk factors — the lipid panel, blood pressure, glucose, body weight, smoking status and family history. A single marker, even in the highest AHA category, is not in itself sufficient grounds for a diagnosis or a treatment decision — that is for the doctor to judge, not the patient.

• Whether there was an infection, fever, injury or recent surgery before the test
• Whether it is worth repeating the hs-CRP test a few weeks later, when the body is settled
• The overall risk picture — lipid panel, blood pressure, glucose, body weight, smoking
• Family history of cardiovascular disease
• Which further tests or monitoring may be appropriate, given the overall picture