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Diagnostic Testing
Noelle Lewis
Molecular Biology
Principles of Genetic testing
A genetic diagnostic test identifies a
specific indicator that shows whether a
person will have or develop a disorder
 Positive test results indicate a person has
the indicator
 Negative test results indicate the indicator
is absent
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Principles of Genetic testing
False positives and negatives are common
 A false positive could result in a person
having unnecessary anxiety and often
unnecessary treatment
 A false negative could result in the person
thinking they do not have the disease
when they actually do
 Clinical tests are adjusted to minimize the
occurrence of false results
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Principles of Genetic testing
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Sensitivity and specificity are used to judge the
clinical validity of a test
Sensitivity is the fraction of correctly identified
people who truly have the indicatorTP
TP+FN
Specificity is the fraction of people who do not
have the indicatorTN
TN+FP
A condition is likely present when a test is positive
and specificity is high.
Testing for genetic disorders
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A test used to identify an inherited disorder
The indicator may be a chromosome, protein,
metabolite, or nucleic acid sequence
Chromosome abnormalities are detected by
karyotype staining or fluorescent in situ
hybridization (FISH).
Biochemical and immunological assays of blood
and urine test amino acids, organic acids, and
metabolites or proteins
-The Guthrie test-Phenylketonuria in infants
Genetic testing
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Accumulation or deficiency of a metabolit
can be detected by tandem mass
spectromery
The m/z pofile is compared to known
standards to identify and quantify the indicator
 Tandem MS is efficient and can detect and
measure the amounts of many different
indicators
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Genetic testing
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Other methods include assays that use the
known human genetic sequence to identify
mutations, single-strand conformation
polymorphism, denaturing gradient gel
electrophoresis, and denaturing highperformance liquid chromatography