IntrinsicfactorisasolidphaseenzymeimmunoassaywithrecombinanthumanintrinsicfactorforthequantitativedetectionofIgGantibodiesagainstintrinsicfactor.Theassayisatoolinthediagnosisofperniciousanaemia(Biermer`sanaemia)Perniciousanaemiaistheendstageofanautoimmunegastritis(typeAgastritis)resultingindestructionofthegastricmucosa.Asmallproportion(10-15%)ofpatientswithautoimmunegastritisdevelopperniciousanaemia.PerniciousanaemiaisthemostcommoncauseofvitaminB12deficiencyinWesternpopulations.Itiscausedbyalackofintrinsicfactor,aglycoproteinneededtoabsorbvitaminB12fromthegastrointestinaltract.Intrinsicfactorisproducedbygastricparietalcells.VitaminB12,inturn,isnecessaryfortheformationofredbloodcells.Perniciousanaemiausuallydoesnotappearbeforetheageof30.Theaverageageatdiagnosisis60years.Infact,onerecentstudyrevealedthatnearly2percentofindividualsover60yearsoldsufferfromperniciousanaemia.FurThermore,slightlymorewomenthanmenareaffected.Thediseasecanaffectallethnicgroups,butoccursmoreoftenamongpeopleofScandinavianorNorthernEuropeandescent.Autoantibodiesinperniciousanaemiatargetparietalcellsandintrinsicfactor.Antibodiesagainstparietalcellsare80-90%sensitivebutcanbedetectedalsoinupto5%ofthehealthypopulation.Antibodiesagainstintrinsicfactorshowasensitivityof50-70%withaspecificityof100%inapopulationofhealthyblooddonors.