Biomedical Engineering Reference
In-Depth Information
simple to use that they are approved to be sold for home use. The
over-the-counter pregnancy test kits sold in drug stores use paired
monoclonal antibody reactive with human chorionic gonadotropin, a
protein hormone that appears in the serum and urine of a pregnant
woman 6 to 15 days after conception (Figure 10.1). A similar technol-
ogy is the basis of some home glucose-monitoring devices for diabetics
who must match their insulin dose to their blood-glucose level.
DNA SEQUENCING TESTS
New, powerful methods of analyzing DNA and RNA have added
to the doctor's tools for detecting and predicting illness. These
methods also have presented profound challenges.
Testing for HIV
The routine test for infection with the human immunodeficiency
virus (HIV) measures whether a person's blood contains antibodies
that react with HIV proteins. Newer tests allow the detection of the
HIV antibody in saliva. Antibody tests are not useful for tracking
how well treatment for HIV infection is working, particularly with
the development of effective drugs that control the ability of the
virus to increase in number. Physicians needed sensitive methods to
detect small numbers of HIV virus in the blood. Three different
FDA-approved tests provide a precise count of the number of HIV
particles by measuring how many copies of the viral RNA genome
are present in the blood plasma, the clear fluid part of the blood
from which the cells have been removed. All of the tests use
probes targeted to sequences of the bases in the viral RNA genome,
and each uses different powerful molecular methods to detect a viral
count as low as 50 copies per milliliter of plasma. In some tests, a
technique called PCR (polymerase chain reaction) makes many
copies of the virus genetic material so that an accurate virus count
can be made with a small sample of blood. These methods can also
detect which type of HIV is present in the sample.
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