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Biologic Markers in Reproductive Toxicology (1989) / Chapter Skim
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Appendix: Assessing the Validity of Biologic Markers: Alpha-Fetoprotein
Pages 311-318

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From page 311...
... The identification of biologic markers that indicate exposure, effect, or susceptibility is a complicated process involving studies animals, refinements in laboratory assays, and studies in special human populations. Moreover, even when a marker has been validated in such studies, its use in larger populations is not straightforward.
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From page 312...
... Figure A- 1 shows the distribution of maternal serum AFP concentrations in normal pregnancies (curve on left) and pregnancies with spine bifida cystica in the fetus (curve on right)
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From page 313...
... Diagnosis of No Indl ation of Affected Fetus Fetal Abnormality Patient Decision Plan for Induced Special Care Abortion at Delivery ~MSAFP = maternal serum alpha-fetoprotein * WAFAFP = amniotic fluid alpha-fetoprotein \`No predictive value of a test in the general population and developing a multistep, multimarker screening protocol.
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From page 314...
... In the clinical or community setting, it is most important to know how likely it is that a positive test indicates disease truly and how likely it is that a negative test indicates the absence of disease truly. The predictive values of tests can be increased
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From page 315...
... VALIDITY OF MATERNAL SERUM AFP MEASUREMENT AS A BIOLOGIC MARKER OF NTDs As indicated earlier, AFP is normally present in amniotic fluid and maternal serum, and it is present in increased concentrations in the presence of anencephaly and spine bifida cystica. Measuring the second-trimester concentration of maternal serum AFP can be used to identify the likelihood that a pregnant woman is carrying a fetus with anencephaly or spine bifida cystica, a ventral wall defect, or twins; other defects can also be predicted.
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From page 316...
... The sensitivity of this test is 0.84, meaning that 16% of babies with anencephaly or spine bifida cystica would be missed. TABLE A-S AFT by Presence or Absence of Neural Tube Defects NTD Marker Present Absent Total Positive Negative Total 334 66 400 3,254 953" 98,600 3,588 95,412 99,000 aData derived from UK Collaborative Study data.
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From page 317...
... References .
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Key Terms

  • serum afp
  • spine bifida
  • priori probability
  • bifida cystica
  • amniotic fluid

  • biologic markers
  • negative total
  • positive negative
  • total positive
  • neural tube

  • predictive value
  • collaborative study
  • normal pregnancies
  • tube defects
  • definitive test

  • biologic marker
  • fluid afp
  • negative test
  • study data
  • disease presence

  • afp tests
  • test indicates
  • screening process
  • adata derived
  • disease truly

  • mistaken gestational
  • marker presence
  • hypothetical data
  • positive test
  • gestational age


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