CRP

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. 

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.

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.

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.