Diagnostic Testing

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Diagnostic Testing

• Noelle Lewis
• Molecular Biology

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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

• 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 indicator-
  TP
• TPFN
• Specificity is the fraction of people who do not
  have the indicator- TN
• TNFP
• A condition is likely present when a test is
  positive and specificity is high.

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Testing for genetic disorders

• 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

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Genetic testing

• 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

• Other methods include assays that use the known
  human genetic sequence to identify mutations,
  single-strand conformation polymorphism,
  denaturing gradient gel electrophoresis, and
  denaturing high-performance liquid chromatography