Inflammation and immunity
CRP
A protein that rises quickly with inflammation or infection; shows whether there is inflammation somewhere, not where or why.
Everything about this testWhat it measures
CRP (C-reactive protein) is a protein that the liver makes in response to inflammation or infection. Within 6 to 8 hours after inflammation starts, the level in the blood rises sharply, and after recovery it falls quickly again, usually within a few days. This makes CRP suitable for showing acute inflammation and following its course. The value says nothing about where the inflammation is.
- Acute infections, especially bacterial infections such as pneumonia
- Inflammatory diseases, such as rheumatoid arthritis or an inflammatory bowel disease
- Tissue damage after surgery, an injury or a heart attack
- The course of an inflammation and the effect of its treatment
High
A raised CRP points to inflammation or infection somewhere in the body. In bacterial infections, such as pneumonia, the value often rises above 100 mg/L; in viral infections the rise usually stays limited. Surgery, an injury and an inflammatory disease such as rheumatism also raise CRP. A slightly raised value is not very specific and also occurs with a cold, overweight, smoking or gum inflammation. Symptoms that go with inflammation are fever, pain, swelling or feeling ill. Rarely: a tumor.
Low
A low or unmeasurable CRP is normal. A low value makes an acute bacterial infection or an active inflammatory disease unlikely, but does not rule it out completely: in the first hours of an infection CRP has not yet risen, and in some diseases, such as lupus or a small local inflammation, the value stays low.
If your result is abnormal
The GP assesses CRP together with the symptoms and the physical examination. A slightly raised value without a clear cause is usually repeated after a few weeks; with a strongly raised or persistently raised value, targeted tests follow to find the source of the inflammation, for example a urine test, a chest X-ray or a referral.
Reliability
CRP is a sensitive but non-specific inflammation marker: a raised value says there is inflammation, not where it is or what causes it. According to the Dutch Society for Clinical Chemistry (NVKC), CRP is mainly useful to make a serious bacterial infection more or less likely and to follow the course; the value can only be interpreted together with symptoms and a physical examination. For inflammation, CRP is preferred over the erythrocyte sedimentation rate (ESR), because CRP responds faster and is less easily disturbed.
Limitations
- In the first 6 to 12 hours of an infection CRP is still low; a measurement taken too early can give false reassurance.
- Overweight, smoking, pregnancy, heavy exercise and small inflammations such as gum inflammation give a slightly raised value without disease.
- Anti-inflammatory drugs such as corticosteroids and biologicals (for example for rheumatism) can suppress the rise in CRP.
- The standard CRP test does not measure low values (below 3 to 5 mg/L) accurately; estimating cardiovascular risk requires the more sensitive hs-CRP.
How common is this
A raised CRP is not a disease but a signal. Infections are the most common cause and are among the most common reasons for a visit to the GP, especially in winter. Chronic inflammatory diseases such as rheumatoid arthritis are less common. There are no Dutch figures on how often a raised CRP is found as an isolated finding.
Who is this useful for
Useful with symptoms that fit an infection or inflammation, such as fever, coughing with shortness of breath, abdominal pain, joint symptoms or long-lasting tiredness with feeling ill, and to follow the course of a known inflammatory disease. In adults without symptoms and without a reason, a CRP yields little: a normal value says little and a slightly raised value is usually harmless. The standard CRP test is not suitable for estimating cardiovascular risk.
Downsides and risks
- CRP does not show a location or cause; a slightly raised value without symptoms often leads to follow-up tests that find nothing.
- A normal CRP early in an infection can give false reassurance.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results