CLINICAL LAB SCIENEC

410
ESSENTIALS OF CLINICAL LABORATORY SCIENCE
In the Lab
IgG coated latex
particles
+
2. Specimens showing gross hemolysis, lipemia, or turbidity should not be used.
3. The strength of agglutination is not indicative of the CRP concentration.
Weak reactions may occur with slightly elevated or markedly elevated CRP
concentrations.
4. Reaction times longer than 2 minutes may cause erroneous results.
5. The Immunex CRP slide test is classified as moderately complex under CLIA ‘88
regulations.
Interpretation of a positive test indicating the presence of CRP for a qualitative procedure
is as follows:
1. A positive result will show visible agglutination and a negative result will appear
smoothly turbid or milky in appearance. A test should be reported as positive
if agglutination is found on either the diluted or the undiluted specimen, as the
sensitivity of the test kit has been adjusted to avoid a large number of positives
for those with normal levels of CRP.
2. When agglutination occurs only in the diluted specimen, it indicates an excess
of antibodies in the undiluted specimen. This is called a prozone reaction and
indicates that results would increase with additional dilutions of the serum.
Agglutination may occur only in the diluted specimen because of high levels of antibody
in the undiluted specimen that are not in proportion to the amount of antigen present.
MANUAL SEROLOGY PROCEDURE #3
Rheumatoid Factor Direct Slide Test (Latex Agglutination)
Principles
A number of methods are available for testing for the rheumatoid factor (RF). RF is
similar to an antigen but is actually based on antibodies against the immune globulins,
Patient serum
containing RF
= latex beads
= human IgG
= RF
Agglutination
of latex
FIGURE 16-3 Principle of latex agglutination test for the rheumatoid
factor and other related antigen-antibody reactions.
Source: Delmar/Cengage Learning.
which in themselves are a reaction against
the disease. This serological test is therefore
slightly different from those that simply test
for antibody production against antigens that
invade the body (Figure 16-3). The rheumatoid
factor (RF) is a high molecular weight protein
that is similar to an antibody and can bind to
other antibodies. In cases of rheumatoid arthritis
(RA), these antibodies bind to IgM antibodies
as though they are antigens, producing agglutination.
Other factors may yield positive results
other than RA. The majority of test kits, such
as the one shown for the Rheumatoid Factor
(Figure 16-4) reveal agglutination on a special
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