rev bras hematol hemoter. 2015;37(5):290–291
w w w . r b h h . o r g
Revista
Brasileira
de
Hematologia
e
Hemoterapia
Brazilian
Journal
of
Hematology
and
Hemotherapy
Scientific
Comment
Impact
on
patient
of
the
detection
of
weakly
expressed
RhD
antigens
in
blood
donors
夽
Helio
Moraes-Souza
a,b,∗,
Vitor
Mendonc¸a
Alves
aaUniversidadeFederaldoTriânguloMineiro(UFTM),Uberaba,MG,Brazil
bHemocentroRegionaldeUberaba/Fundac¸ãoHemominas,Uberaba,MG,Brazil
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Articlehistory:
Received14July2015 Accepted28July2015 Availableonline5August2015
Due to blood transfusions, pregnancy, and organ/tissue transplantsorgrafts,1redblood cellalloimmunizationmay leadtoseriouscomplications,suchashemolytictransfusion reactions,2–4 whichhavebeen regardedas oneofthe most frequentcausesoftransfusion-relateddeathsinrecentyears accordingtoreportsfromtheFoodandDrugAdministration (FDA).5
Rh,themostcomplexbloodgroupsystem,hasthehighest clinical importanceafter the ABO group.6,7 The Dantigen, foundinRh-positiveindividuals,isthemostimportantinthe systemasitisthemostimmunogenic.7,8Therefore,giventhe riskofalloimmunization,RhD-positiveredbloodcellsmust notbetransfusedtoRhD-negativepatientsexceptin emer-genciesinvolving massive hemorrhagewhen RhD-negative unitsarenotavailable.7
TheRhDproteinhas417aminoacidsdividedintoseven intracellularsegments,twelvetransmembranesegmentsand sixextracellularsegments.9Aminoacid substitutioninthe intracellularortransmembranesegmentoftheRhDprotein leadstoweakeningoftheDantigenexpressioninthe mem-braneofredbloodcellsresultinginaweakDphenotype.6–13 Hence,weakD testingmust alwaysbe performedinblood
DOIoforiginalarticle:http://dx.doi.org/10.1016/j.bjhh.2015.06.001. 夽
SeepaperbySchmidtetal.onpages302-5.
∗ Correspondingauthorat:UniversidadeFederaldoTriânguloMineiro(UFTM),Av.GetúlioGuaritá,250,Abadia,38025-440Uberaba,MG,
Brazil.
E-mailaddress:helio.moraes@dcm.uftm.edu.br(H.Moraes-Souza).
donorswithabsentreactivityinthescreeningtest,andifthe resultsareweaklypositive,thedonorsmustbeclassifiedas RhD-positiveinordertopreventanti-Dalloimmunizationin RhD-negativepatientswhoreceivetransfusionsofpackedred bloodcells.6–8,10
From the 1980s, the introduction of monoclonal anti-D reagentsintheUnitedStateshavehelpedtoincreaseweak Dantigendetectionbyusingserologicalmethods.Inroutine laboratoryinvestigations,bloodsamplesarefoundtohavethis phenotypewhenthereactivityofredbloodcellswithanti-D serumisabsentorweaklypositive(≤2+)inthescreeningtest, yetwithmoderateorstrongagglutinationwhenantiglobulin serumisadded,10orwhenRhDgenotypingisdemonstrated bymolecularmethods.
Nonetheless,insomecases,standardserologicalmethods maynotdetectredbloodcellswiththeweaklyexpressedD antigenandthus,RhD-positivedonorsareerroneouslytyped as RhD negative,11,13 despitethe improvement inthe sen-sitivity ofdetectionthat hasbeenobserved usingdifferent monoclonalantibodyreagents.
AstudybySchmidtetal.14showedpositiveresultsforthe RhD antigenin 5.9%of 152 blood donors– who had been
http://dx.doi.org/10.1016/j.bjhh.2015.07.007
revbrashematolhemoter.2015;37(5):290–291
291
previously identified as RhD negative in routine examina-tions–whenusinganti-DIgGmonoclonalantibodies(clones ESD1,MS-26andTH-28)ingelcards.Inthesamestudy,the authorsevaluatedanotherpopulationof4897donorsfrom dif-ferentregionsofMinasGeraisstate,Brazil,whohadallbeen previouslyphenotypedasDnegativeintheindirect antiglob-ulintest(IAT),withclonesMS-26andTH-28,and70(1.43%) individuals showed weakreactivity with ESD1anti-D anti-bodies. Molecular analysis were performed for 39 ofthese 70individualswithRHDpositivityconfirmedbyamultiplex RHDgenotypingassay,whereasothermoleculartechniques suchaspolymerasechainreaction-sequence-specificprimers (PCR-SSP) and RHD BeadChip were effective inspecifically identifyingdifferentRHDvariantsin48.71%ofthese39RHD positivesamples. However, it would beimportantthat the negativesamplesofESD1anti-Dclonewerealsosubjectedto molecularanalysissoastoestablishthelevelofsensitivityof thisantiserum.
Costaetal.15found,bymolecularmethods,that18(3.4%) of520 donorspreviously classifiedas RhD negativeinSão Paulo, Brazil,carried different RHD variants. Moreover,the authorsobservedthatfour(22.2%)ofthese18individualshad anegativeIAT,eventhough11 differentmonoclonalanti-D antibodies (including clone ESD1) were used, whereas the otherindividualsshowedaweakorverypoorreactiontofive oftheseantibodies, aswell as negativereactions tosix of theseantisera.
Itisconsensusthatmoleculartechniquesallowedthestart ofanewstageofblooddonortyping,includingseveral strate-giestoidentifyRhDvariantsthatarepotentiallyimmunogenic in apparently RhD-negative donors, as shown in several studies.11–17Furthermore,insomeofthesestudies,these vari-antswerealsofoundtobeassociatedwiththeCandEantigens oftheRhsystem,11,12,14,15althoughsomeRhDsubtypeswere foundincceeindividuals.13Techniqueshavenowidentified morethan200variantsoftheDantigen,includingweakD, DpartialandDELtypes.16Ofthistotal,over80belongtothe weakDphenotype(11),withsubtypes1,2and3beingthemost prevalent.10Itisknownthat0.2–1%ofEuropeanandAmerican Caucasianindividualsarecarriersofthisphenotype.10
Advancesin serologicaland molecular techniques have madethedetectionofthedifferentvariantsofRhD increas-inglymoreaccurateinrecentyears.Donorswhowereonce typedasRhDnegativehavebeenreclassifiedasRhDpositive, henceincreasingtransfusionsafetyforRhD-negativepatients. Therefore,theadoptionofimprovedserologicalmethodsand inparticularmolecular techniquesis keyto theroutine of immunohematologylaboratoriestostandardizeteststo iden-tifyweaklyexpressedDantigensandotherRhDvariants.This procedureallowsthecorrectclassificationoftheRhDstatus ofblood donors,thusminimizingtheriskofanti-D alloim-munization and hemolytic reactions, as well as increasing transfusionsafetyofRhD-negativepatients,includingwomen ofchildbearingage,receivingtransfusionsofpackedredblood cells.Therefore,hemolyticdiseaseofthefetusandnewborn byantibodiesdirectedagainstDantigenisprevented.
Conflicts
of
interest
Theauthorsdeclarenoconflictsofinterest.
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