title: Interference in the autoDELFIA(R) hAFP immunoassay and effect on second-trimester Down's syndrome screening.
abstract: BACKGROUND
  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.
authors.affiliation: Department of Medical Biochemistry and Immunology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, UK.
authors.forename: Leanne
authors.initials: L
authors.lastname: Mannings
authors.forename: Sandy
authors.initials: S
authors.lastname: Trow
authors.forename: Janet
authors.initials: J
authors.lastname: Newman
authors.forename: Barry
authors.initials: B
authors.lastname: Nix
authors.forename: Carol
authors.initials: C
authors.lastname: Evans
mesh_terms: D003165:Complement System Proteins / Q000737:chemistry; D004314:Down Syndrome / Q000175:diagnosis*; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008403:Mass Screening / Q000379:methods; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis / Q000379:methods*; D018570:Risk Assessment; D000509:alpha-Fetoproteins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000509:alpha-Fetoproteins; D003165:Complement System Proteins