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Interference in the autoDELFIA(R) hAFP immunoassay and effect on second-trimester Down's syndrome screening.

AbstractBACKGROUND:
Falsely decreased serum alphafetoprotein (AFP) concentrations are reported in the autoDELFIA(®) hAFP immunoassay due to interference by complement. AFP is measured, using this assay, as part of second-trimester and integrated Down's syndrome screening tests. Decreased AFP concentrations increase the calculated risk of Down's syndrome; therefore falsely low AFP, due to assay interference, may artificially increase a patient's risk, and have the potential to cause false screen positive results. It was our aim to assess whether negative interference in the autoDELFIA(®) hAFP assay was a cause of very low AFP concentrations, and to examine the effect of falsely decreased concentrations on the calculated risk of Down's syndrome.
METHODS:
Three hundred and twenty-three sequential Down's screening serum samples with very low serum AFP concentration (<15 KU/L) using the autoDELFIA(®) hAFP immunoassay were selected and AFP re-measured using the E170 AFP immunoassay.
RESULTS:
Interference was detected in nine samples (from eight patients) on the basis of discordant AFP concentrations. The interference decreased following storage of samples at 4°C to deplete complement. Use of the falsely low AFP concentrations to calculate risk of Down's syndrome resulted in significantly increased calculated risk compared with complement depleted results.
CONCLUSIONS:
Laboratories should be aware that falsely low AFP concentrations due to complement interference may be obtained using the autoDELFIA(®) hAFP immunoassay. We have shown that falsely low AFP concentrations increase the calculated risk of Down's syndrome. This is a potential cause of false Down's syndrome screen positive results.
AuthorsLeanne Mannings, Sandy Trow, Janet Newman, Barry Nix, Carol Evans
JournalAnnals of clinical biochemistry (Ann Clin Biochem) Vol. 48 Issue Pt 5 Pg. 438-40 (Sep 2011) ISSN: 1758-1001 [Electronic] England
PMID21795408 (Publication Type: Journal Article)
Chemical References
  • alpha-Fetoproteins
  • Complement System Proteins
Topics
  • Complement System Proteins (chemistry)
  • Down Syndrome (diagnosis)
  • False Negative Reactions
  • False Positive Reactions
  • Female
  • Humans
  • Immunoassay (methods)
  • Mass Screening (methods)
  • Pregnancy
  • Pregnancy Trimester, Second
  • Prenatal Diagnosis (methods)
  • Risk Assessment
  • alpha-Fetoproteins (chemistry, metabolism)

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