CRP level: what is it, normal values and what does an abnormality mean?

Your CRP level is one of the most commonly measured blood values. CRP stands for C-reactive protein, a protein your liver produces in response to inflammation. An elevated CRP can be a signal that an inflammatory process is happening somewhere in your body.

Many people see their CRP level without knowing exactly what the number means. A mildly elevated value quickly raises questions, even though it is often not a sign of anything serious.

This article explains what CRP is, what the normal values are and what an elevated or low CRP can mean. It also covers hs-CRP, CRP during pregnancy, when a measurement is less reliable and what you can do yourself through lifestyle.

What is CRP?

C-reactive protein is an acute-phase protein. Your body produces it quickly during infection, inflammation or tissue damage. Production starts in the liver, driven by signalling substances from the inflamed area.

CRP responds relatively quickly. The value can rise within six to eight hours and often peaks after about two days. Once the cause resolves, CRP also falls promptly, because the protein has a short lifespan.

CRP is a non-specific marker. It can indicate that inflammation is present, but not where it is or what causes it. That broad sensitivity makes CRP useful as a general screening value.

For this reason CRP is usually viewed alongside other blood values, which gives your doctor more context than a single number.

Normal CRP values

CRP is measured in mg/L (milligrams per litre). The table below gives a general classification of the reference values. Laboratories may use small differences in their reference ranges.

A one-off, mildly elevated value is not in itself a reason for concern. The context, your symptoms and the trend over time are often more informative than a single number.

Why your CRP value can fluctuate

Your CRP value is not a fixed figure. A recent cold, a small wound, a dental procedure or intensive exercise can temporarily raise it.

This is why a repeated measurement often says more than a single result. If the value drops again over time, that fits a passing cause. If it stays elevated, that is a reason to look further.

What does an elevated CRP mean?

An elevated CRP means an inflammatory response is happening somewhere in your body. The height of the value mainly says something about the intensity of that response, not the location or the exact cause.

Broadly, a higher value fits a stronger inflammatory stimulus. A markedly elevated value more often fits a bacterial infection, while a mild rise can have many different backgrounds.

The causes can broadly be divided into acute and chronic causes.

Acute causes

• Infections - bacterial infections often cause a strong CRP rise, viral infections usually a milder one.
• Injuries or surgery - tissue damage temporarily activates the inflammatory response.
• Acute inflammation - such as appendicitis or pneumonia.

Chronic causes

• Autoimmune diseases - such as rheumatoid arthritis, Crohn's disease or lupus.
• Chronic infections - long-lasting infections the body does not fully clear.
• Excess weight - fat tissue can produce inflammatory substances that mildly raise CRP.
• Smoking - can contribute to chronic low-grade inflammation.
• Long-term stress - is associated with a mildly raised degree of inflammation.

Because CRP itself does not say where the inflammation is, your doctor may suggest further testing. An elevated value is mainly a reason to look further, together with your symptoms and possibly other blood tests.

CRP in specific conditions

CRP in pneumonia and infections

In pneumonia the CRP level is often clearly elevated. Doctors sometimes use CRP to gauge how an infection develops and whether a treatment is taking effect.

In bacterial infections the value is on average higher than in viral infections. Even so, CRP is never proof on its own: the picture is always reviewed alongside your symptoms and a physical examination.

CRP in autoimmune diseases

In autoimmune diseases such as rheumatoid arthritis, CRP can be elevated for a long time. The value can help reflect the degree of inflammatory activity, alongside other blood values such as the sedimentation rate.

A changing CRP value can be an indication that disease activity is increasing or decreasing. Interpreting that belongs with the doctor treating the condition.

CRP in cardiovascular disease

In cardiovascular disease, low-grade inflammation plays a role in the process of artery hardening. For this context the more sensitive hs-CRP is usually used rather than standard CRP.

hs-CRP is then reviewed alongside other risk factors, such as cholesterol and blood pressure. None of those values stands on its own; together they form a risk profile.

A low CRP value: what does it mean?

A low CRP value is usually a reassuring sign. It means that at the moment of measurement there is no indication of significant inflammation in your body.

Unlike some other blood values, CRP has no lower limit that is problematic. A value below 5 mg/L simply falls within the normal range.

It is worth knowing that a normal CRP does not rule out every condition. Some chronic complaints cause little or no rise in CRP, so other blood values may then tell you more.

hs-CRP: the sensitive variant

Alongside standard CRP there is hs-CRP (high-sensitivity CRP). It measures the same marker, but with greater precision in the low range, so small differences become visible.

hs-CRP is mainly used to estimate cardiovascular risk. The general classification is below 1 mg/L for low risk, 1 to 3 mg/L for moderate risk, and above 3 mg/L for elevated risk, provided no acute infection is present.

An acute infection can temporarily raise hs-CRP considerably. For a reliable estimate of your risk profile, the measurement is therefore best done when you feel healthy.

hs-CRP is not a standalone test you can score as good or bad, but one piece of a broader picture of your cardiovascular health.

When is a CRP measurement less reliable?

CRP is a valuable marker, but there are situations in which the result is harder to interpret. It helps to know these before drawing conclusions.

• Shortly after an infection, surgery or significant physical exertion, the value can still be elevated without anything new being wrong.
• During pregnancy CRP is naturally somewhat higher.
• Anti-inflammatory medications can lower the value.

In these cases a repeated measurement at a calm moment often gives a clearer picture than a single result.

CRP and pregnancy

During pregnancy the CRP value can naturally be slightly elevated. This fits the normal changes the body goes through in this period.

A slight rise is therefore not immediately a cause for concern. Whether a value is appropriate is best assessed by your midwife or doctor within the context of your pregnancy.

A markedly elevated value, or symptoms such as fever, should be discussed. Your care provider then looks at the overall picture rather than at CRP alone.

CRP and lifestyle: what can you do yourself?

A chronically, mildly elevated CRP is sometimes linked to lifestyle factors, and you have some influence over those factors yourself.

• Weight - with excess weight, weight loss may contribute to a lower degree of inflammation.
• Nutrition - a diet rich in vegetables, fruit and fibre is often associated with less low-grade inflammation.
• Exercise - regular physical activity may have a favourable effect on inflammatory values.
• Smoking - stopping smoking can reduce the chronic inflammatory stimulus.

Enough sleep and limiting long-term stress are also associated with lower inflammatory values. Do not expect a quick change: lifestyle effects usually become visible only over weeks to months.

Lifestyle is not a substitute for medical care, but it can form a well-founded basis.

What to do with an elevated CRP

An elevated CRP is a reason to look further, not a reason to panic. In many cases there is an obvious, passing cause.

The following steps are common:

• Check whether there is an obvious cause, such as a cold, a recent injury or surgery.
• With a persistently elevated CRP and no clear cause, you can discuss this with your GP.
• Your doctor may suggest further blood testing to identify the cause.

Sometimes a mildly elevated value is linked to vague complaints such as fatigue.

Having your CRP measured

CRP is often included in a broader blood test. At Vital Check, CRP is part of the Extended Health Checkup, which also maps a number of other relevant blood values.

You do not need to fast for a CRP measurement, and a GP referral is not required. You can visit one of the affiliated sample-collection locations.

Every blood test result includes a professional assessment from a BIG-registered doctor, so you are not left alone with a set of loose numbers. A blood test does not make a diagnosis. For treatment decisions, discuss your results with your GP.