Dr Leigh Martens

General Practitioner

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Blood-tests Explained


Disclaimer:

This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

CRP


At a Glance

Why Get Tested?

To identify the presence of inflammation and to monitor response to treatment for an inflammatory disorder

When to Get Tested?

When your healthcare provider suspects that you have an acute condition causing inflammation, such as a serious bacterial or fungal infection or when you are suffering from an inflammatory disorder such as arthritis, an autoimmune disorder, or inflammatory bowel disease

Sample Required?

A blood sample taken from a vein in your arm

Test Preparation Needed?

None

The Test Sample

What is being tested?

C-reactive protein (CRP) is an acute phase reactant, a protein made by the liver and released into the blood within a few hours after tissue injury, the start of an infection, or other cause of inflammation. Markedly increased levels are observed, for example, after trauma or a heart attack, with active or uncontrolled autoimmune disorders, and with serious bacterial infections like sepsis. The level of CRP can jump as much as a thousand-fold in response to inflammatory conditions, and its rise in the blood can precede pain, fever, or other clinical indicators. The test measures the amount of CRP in the blood and can be valuable in detecting inflammation due to acute conditions or in monitoring disease activity in chronic conditions.

The CRP test is not diagnostic, but it provides information to a health practitioner as to whether inflammation is present. This information can be used in conjunction with other factors such as signs and symptoms, physical exam, and other tests to determine if someone has an acute inflammatory condition or is experiencing a flare-up of a chronic inflammatory disease. The health practitioner may then follow up with further testing and treatment.

This standard CRP test is not to be confused with an hs-CRP test. These are two different tests that measure CRP and each test measures a different range of CRP level in the blood for different purposes:

  • The standard CRP test measures markedly high levels of the protein to detect diseases that cause significant inflammation. It measures CRP in the range from 10 to 1000 mg/L.
  • The hs-CRP test accurately detects lower levels of the protein than the standard CRP test and is used to evaluate individuals for risk of cardiovascular disease. It measures CRP in the range from 0.5 to 10 mg/L. (See the article on hs-CRP.)

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

How is it used?

The C-reactive protein (CRP) test is used by a health practitioner to detect inflammation. CRP is an acute phase reactant, a protein made by the liver and released into the blood within a few hours after tissue injury, the start of an infection, or other cause of inflammation. The CRP test is not diagnostic of any condition, but it can be used together with signs and symptoms and other tests to evaluate an individual for an acute or chronic inflammatory condition.

For example, CRP may be used to detect or monitor significant inflammation in an individual who is suspected of having an acute condition, such as:

  • A serious bacterial infection like sepsis
  • A fungal infection
  • Pelvic inflammatory disease (PID)

The CRP test is useful in monitoring people with chronic inflammatory conditions to detect flare-ups and/or to determine if treatment is effective. Some examples include:

  • Inflammatory bowel disease
  • Some forms of arthritis
  • Autoimmune diseases, such as lupus or vasculitis

CRP may sometimes be ordered along with an erythrocyte sedimentation rate (ESR), another test that detects inflammation. While the CRP test is not specific enough to diagnose a particular disease, it does serve as a general marker for infection and inflammation, thus alerting health practitioners that further testing and treatment may be necessary. Depending on the suspected cause, a number of other tests may be performed to identify the source of inflammation. 

When is it ordered?

The CRP test may be ordered when an individual is suspected of having a serious bacterial infection based on the person's medical history and signs and symptoms. It may be ordered, for example, when a newborn shows signs of infection or when an individual has symptoms of sepsis, such as fever, chills, and rapid breathing and heart rate.

It may also be ordered on a regular basis to monitor conditions such as rheumatoid arthritis and lupus and is often repeated at intervals to determine whether treatment is effective. This is particularly useful for inflammation problems since CRP levels drop as inflammation subsides.

What does the test result mean?

The level of CRP in the blood is normally low. 

A high or increasing amount of CRP in the blood suggests the presence of inflammation but will not identify its location or the cause. In individuals suspected of having a serious bacterial infection, a high CRP can be confirmatory. In people with chronic inflammatory conditions, high levels of CRP suggest a flare-up or that treatment has not been effective.

If the CRP level is initially elevated and drops, it means that the inflammation or infection is subsiding and/or responding to treatment.

Is there anything else I should know?

CRP levels can be elevated in the later stages of pregnancy as well as with use of birth control pills or hormone replacement therapy (i.e., estrogen). Higher levels of CRP have also been observed in people who are obese.

The erythrocyte sedimentation rate (ESR) test will also be increased in the presence of inflammation; however, CRP increases sooner and then decreases more rapidly than the ESR.