Definition

C-reactive protein (CRP) is a protein released by the liver in response to inflammation or cellular damage caused by factors such as infections, trauma, autoimmune disorders, or malignancies. The protein enters the bloodstream during acute-phase responses, typically several hours after tissue damage, infection, or the onset of inflammation. Under normal circumstances, CRP levels in the blood are minimal. An elevated CRP level signals an acute condition, such as infection, inflammation, tissue damage, or malignancy, prompting the liver to produce more CRP than usual.

The CRP test requires a blood sample to assess acute conditions such as infection, inflammation, or tissue damage. However, the test is nonspecific and cannot diagnose a specific disease, as elevated CRP levels may result from various conditions. Additional tests are necessary to confirm the underlying cause.

CRP testing can be conducted using two methods: qualitative and quantitative. Qualitative testing involves a blood clotting method that reacts with latex reagents, while quantitative testing employs a dilution method. The qualitative test is more commonly used due to its simplicity in detecting elevated CRP levels in the blood.

Indications

Qualitative CRP testing can be performed under the following conditions:

• Severe bacterial infections
• Sepsis, an extensive body-wide infection causing decreased consciousness and life-threatening complications
• Liver infections such as hepatitis
• Inflammatory bowel disease (IBD), characterized by intestinal inflammation and swelling
• Autoimmune diseases, including Systemic Lupus Erythematosus (SLE), rheumatoid arthritis, and inflammatory vascular conditions
• Bone infections, such as osteomyelitis
• Monitoring the effectiveness of therapy in patients with chronic infections
• Assessing the risk of disease in patients with high-risk factors for heart disease
• Detecting potential infections in patients after surgical procedures, typically tested three days post-surgery

Contraindications

There are no absolute contraindications for qualitative CRP testing.

Preparation Before the Test

This test involves taking a blood sample, which is a common and routine medical procedure. No special preparations are required; you can eat, drink, and carry on with your daily activities as usual. The procedure is generally safe and can be performed at any time when necessary. Potential side effects include slight pain or bruising at the injection site and, in rare cases, minor bleeding.

Test Procedure

The qualitative CRP test involves blood collection and laboratory clotting analysis. The steps are as follows:

1. Blood is drawn by identifying a suitable vein, typically in the upper arm.
2. The site is cleaned with an alcohol swab in a circular motion from the center outward and allowed to dry.
3. A tourniquet is applied to the upper arm to make the vein more prominent by restricting blood flow.
4. A needle is inserted into the vein, and 5 ml of blood is collected into a tube for the test.
5. The tourniquet is released as soon as the blood begins to flow into the tube.
6. Once the required amount of blood is collected, the needle is removed, and the puncture site is pressed with a cotton swab soaked in alcohol to prevent further bleeding.
7. The blood sample is then sent to the laboratory for a clotting test to measure CRP levels.

In the lab, the following steps are conducted:

1. The necessary equipment is prepared.
2. One drop of negative control, positive control, and the blood sample or serum is placed on designated circles on a plate holder.
3. A drop of latex reagent is added to each circle.
4. The contents of each circle are stirred with a stick to mix the latex reagent with the blood serum or control fluids.
5. The mixture is left for two minutes to observe for clotting.
6. After two minutes, the samples are inspected for signs of clotting.

Normal and Abnormal Values

Normal Values

A normal result shows no clotting in the blood serum during the test. This indicates that CRP levels in the blood are too low to react with the latex reagent, suggesting no significant inflammation.

Abnormal Values

An abnormal result is indicated by clotting in the blood serum. This means CRP levels are elevated, typically at 10 mg/dL or higher, which triggers a reaction with the reagent.

Normal CRP levels are within 5–10 mg/dL, and levels above 10 mg/dL signify high CRP levels associated with inflammation caused by various diseases.

Results and Recommendations (Further Testing)

Positive

A positive result indicates elevated CRP levels, which could be due to acute bacterial infections, severe body infections, fungal infections, acute inflammation, or chronic inflammatory conditions. However, qualitative CRP tests cannot pinpoint the location or specific cause of inflammation. Doctors may recommend further tests, such as a complete blood count, urinalysis, chest X-ray, or ANA (antinuclear antibody) tests.

Negative

Consult the Right Doctor

If your qualitative CRP test results indicate a positive result or show levels above the normal range, it is recommended to consult a general practitioner or an internal medicine specialist to discuss the findings and their implications. For children with similar test results, seeking advice from a pediatrician is essential. The doctor will interpret the test results in conjunction with a direct examination to provide appropriate recommendations.

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