C-Reactive Protein (CRP) Test: Introduction, Principle, Testing Procedure, Result -Interpretation, Normal Range, Clinical Significance, and Other Methods of Testing
Table of Contents
C-Reactive Protein (CRP) is a carbohydrate-reactive protein. The C-Reactive Protein (CRP) Test was so named because it was first identified as a substance in the serum of patients with acute inflammation that reacted with the somatic ‘C’ carbohydrate antigen of Pneumococcus. Discovered by Tillett and Francis in 1930. Synthesized by hepatocytes. CRP is an annular pentameric protein found in plasma, whose levels rise in response to inflammation. Molecular Weight 25,106 Dalton. An acute-phase protein of hepatic origin that increases following interleukin-6 secretion by macrophages as well as adipocytes in response to a wide range of acute and chronic inflammatory conditions such as bacterial, viral, or fungal infections; rheumatic and other inflammatory diseases; malignancy; and tissue injury and necrosis.
Elevated in 6-10 hours of inflammation and rises up to thousands of times Plasma half-life- 19 hours and falls within a few days. CRP binds to the phosphocholine expressed on the surface of dead or dying cells and some bacteria. This activates the complement system via the C1Q complex, promoting phagocytosis by macrophages, which clears necrotic and apoptotic cells and bacteria. It plays a role in innate immunity as an early defense system against infections.
The method was introduced by Singer, et. al., in 1957. This is a slide agglutination test for the qualitative and semi-quantitative detection of C-Reactive Protein (CRP) in human serum. Latex particles coated with goat IgG anti-human CRP are agglutinated when mixed with samples containing CRP. When latex particles coated with human anti-CRP are mixed with a patient’s serum containing C – reactive proteins, this results in visible agglutination within 2 minutes.
Bring all reagents and serum samples to Room Temperature and mix latex reagent gently prior to use. Do not dilute the controls and serum. Place 50 ul each of serum, positive control, and negative control on separate reaction circles. Then add CRP latex reagent 1 drop to each of the circles. Mix with separate mixing sticks and spread the fluid over the entire area of the cell. Tilt the slide back and forth slowly for 2 minutes observing preferably under artificial light.
| Positive | Agglutination of latex particles, indicating the presence of C – reactive protein at a significant and detectable level |
| Negative | No Agglutination |
| Negative Control(NC) | Negative |
| Positive Control(PC) | Positive |
| Test | showing clumping/ agglutination, therefore the test is positive as shown above in the figure |
Using isotonic saline prepare serial dilutions of the patient’s serum (1/2, 1/4, 1/8, 1/16, 1/32, 1/64, and so on). Transfer 50ul of each serum dilution to a test circle on the slide. Shake the reagent, then add one drop of suspension to the test circle. Mix the drops using a disposable stirrer ensuring coverage of the test circle with the mixture. Place the test slide on the bench and leave for 2 minutes. Gently and evenly, rock and rotate the test slide once and place the test slide on the bench once more. One minute later, read the test slide for the presence of agglutination.
CRP mg/dl = 6 (can vary) x D,
where D is the highest dilution of serum showing agglutination and 6 is the sensitivity in mg/L.
0-10 mg/L
Conditions associated with an elevated level of CRP-
Moderate elevation (0-10mg/dL)
Marked elevation(>10 mg/dL)
The risk of developing cardiovascular disease is quantified as follows:
An especially high CRP reading of greater than 10 mg/L may indicate:
Various Methods to Measure CRP tests are as follows-
A high-sensitivity CRP (hs-CRP) test measures low levels of CRP using laser nephelometry. The test gives results in 25 minutes with a sensitivity down to 0.04 mg/dL.
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