C-Reactive Protein

Test Description:

C-reactive protein (CRP) is a glycoprotein produced by the liver, which is normally
absent from the blood. The presence of acute inflammation with tissue destruction
within the body stimulates its production. Therefore, a positive CRP indicates the
presence of an inflammatory process. When the acute inflammation is no longer
present, the CRP rapidly dissipates from the body. The CRP typically rises within
6 hours of the start of inflammation, allowing the inflammation to be confirmed
much sooner than through the use of the erythrocyte sedimentation rate (ESR),
which usually increases about a week after inflammation begins.
There are two types of CRP which can be measured. The standard CRP is used to
assess how active inflammation is in such chronic problems as inflammatory bowel
disease, arthritis, and autoimmune diseases; to assess for a new infection such as in
appendicitis and postoperative conditions; and to monitor response to treatment of
these conditions. The other type of CRP is high-sensitivity CRP (hs-CRP). This substance
is considered a marker of low-grade vascular inflammation, which is a key
factor in the development and rupture of atheromatous plaque. Elevated CRP levels
predict future coronary events, stroke, peripheral vascular disease, and type 2 diabetes
mellitus. Thus this test is used to assess risk of cardiovascular problems in conjunction
with other testing, such as measuring cholesterol levels.

THE EVIDENCE FOR PRACTICE

When dealing with such problems as rheumatoid arthritis, skin infections, and pelvic
inflammatory disease, laboratory tests include the acute phase reactants (APRs), erythrocyte
sedimentation rate (ESR), and C-reactive protein (CRP). These two APRs are good indicators
of the inflammatory activity of such diseases.
Measurement of serum CRP concentration may be helpful in determining use of antibiotics
in patients with CSF findings consistent with meningitis, but for whom the Gram stain
result is negative. This recommendation is based on data showing that a normal CRP has a
high negative predictive value in the diagnosis of bacterial meningitis
Current research is continuing to look at the utility of hs-CRP in cardiovascular risk
prediction, especially in women and in those with metabolic syndrome, to predict risk for
colon cancer development, and as a marker for lung lesion progression.

Normal Values

CRP:              0–1.0 mg/dL or <10 mg/L (SI units)

hs-CRP (assessing risk of CV disease): 

                         <1.0 mg/L = Lowest risk
                         1.0–3.0 mg/L = Average risk
                          >3.0 mg/L = Highest risk

Possible Meanings of Abnormal Values

Increased CRP                                            Increased hs-CRP

Acute pancreatitis                                       Increased risk of cardiovascular disease
Appendicitis
Bacterial infection
Burns
Increased risk of colon cancer development
Inflammatory bowel disease
Lupus
Lymphoma
Myocardial infarction
Pelvic inflammatory disease
Polymyalgia rheumatica
Rheumatoid arthritis
Sepsis
Surgery (first 3 post-op days)
Tuberculosis

Contributing Factors to Abnormal Values

• False-negative: medications including nonsteroidal anti-inflammatory drugs (NSAIDs),
aspirin, corticosteroids, statins, beta blockers
• False-positive: medications including hormone replacement therapy, oral contraceptives
• Use of an intrauterine device (IUD)
• Vigorous exercise
• Pregnancy
• Obesity

Interventions/Implications

Pretest

• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• Laboratories may vary in preparation for the test: some require no preparation while others
require fasting for 4 to 12 hours before the test. Water is allowed.

Procedure

• A 5-mL blood sample is drawn in a green-top collection tube
• Gloves are worn throughout the procedure

Posttest

• Apply pressure at venipuncture site, periodically assessing for continued bleeding, apply
dressing.
• Label specimen and transport to the laboratory immediately.
• Report abnormal findings to the primary care provider.

Clinical Alerts            

• The patient with elevated hs-CRP levels should be counseled on ways to reduce
cardiovascular disease risk, and may require additional diagnostic testing to
determine the presence of beginning cardiovascular disease.
• Elevated CRP levels should be correlated with other diagnostic results, such as
elevated white blood count, to further narrow the list of possible causes of the
abnormal finding.