C-reactive protein (CRP) is a protein produced by the liver during inflammation. CRP levels rise within hours of inflammation or tissue injury and interact with the immune system's complement pathway. The CRP test is used to detect inflammation and monitor conditions involving infection, injury, or disease by checking for elevated CRP levels, which normally return to baseline after treatment or healing. An elevated CRP can indicate infection, injury, or inflammatory conditions like arthritis but does not diagnose a specific disease.

1. What is C-reactive protein (CRP)?
C-reactive protein (CRP) is a special type of protein
produced by the liver in response to inflammatory
cytokines such as Interleukin-6 (IL-6).
CRP is classified as an acute phase reactant, which
means that its levels will rise within a few hours after
tissue injury, the start of an infection, or other cause
of inflammation.
The most important role of CRP is its interaction
with the complement system, which is one of the
body’s immunologic defense mechanisms.

2. Why CRP test is done?
• C-reactive protein (CRP) test is performed to determine if a person
has a problem linked to acute infection or 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. These
include:
• To determine if there is infection after surgery: CRP levels normally
increase within two to six hours following surgery but then return
to normal by the third day; if CRP levels are elevated three days
after surgery it means there is an infection.
• To keep track of an infection or disease that can cause
inflammation: Inflammatory bowel disease (IBD), lymphoma
(cancer of the lymph nodes), immune system diseases such as lupus
(SLE), rheumatoid arthritis ( swelling of the tissues that line the
joints) and osteomyelitis (infection of the bone) are some
conditions in which inflammation can be monitored with a CRP test.
• To monitor treatment of a disease such as cancer or infection: Not
only do CRP levels go up quickly if you have an infection but they
also return to normal quickly if you are responding to the
treatment.

3. • In general, the main causes of increased CRP and
other markers of inflammation are a variety of
conditions, including
• burns,
• trauma,
• infections, such as pneumonia or tuberculosis,
• heart attack,
• chronic inflammatory diseases such
as lupus, vasculitis, or rheumatoid arthritis,
• inflammatory bowel disease, and
• certain cancers.

4. • CRP tests for heart disease
• It's thought that a high level of hs-CRP in your blood is associated
with an increased risk of heart attacks. A CRP test doesn't indicate the
cause of inflammation, though, so it's possible that a high hs-CRP
level could mean there's inflammation caused by something besides
your heart.
• The American Heart Association doesn't recommend an hs-CRP test
for everyone. Rather, the test is most useful for people who have a 5
to 10 percent chance of having a heart attack within the next 10
years. This intermediate risk level is determined by the global risk
assessment, which is based on lifestyle choices, family history and
current health status.
• The test also helps determine the risk of a second heart attack, as
people with a high level of hs-CRP who had a heart attack are more
likely to have another event than those with a normal level.
• People who have a low risk of having a heart attack are less likely to
benefit from having an hs-CRP test. People who have a known high
risk of having a heart attack should seek treatment and preventive
measures regardless of how high their hs-CRP level is.

5. CRP Test Principle
• CRP Test is based on the latex agglutination method
introduced by Singer, et. al., in 1957.
• This is a slide agglutination test for the qualitative and
semiquantitative 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 wihtin 2 minutes.
• For a standard CRP test, a normal reading is less than 10
milligram per liter (mg/L). A test result showing a CRP
level greater than 10 mg/L is a sign of serious infection,
trauma or chronic disease, which likely will require further
testing to determine the cause

6. CRP Test Procedure (Qualitative)
• Bring all reagents and serum sample to Room
Temperature and mix latex reagent gently prior to
use. Do not dilute the controls and serum.
• Place 1 drop 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.

7. Interpretation
 Agglutination of latex particles is considered a positive reaction,
indicating the presence of C-reactive protein at a significant and
detectable level.
 Specimens which do not contain human CRP will not cause
agglutination.
If controls do not give expected reactions the test is invalid and must
be repeated.