neonatal alloimmune thrombocytopenia: diagnosis, management, investigations

Neonatal Alloimmune Thrombocytopenia:Diagnosis, Management, Investigations

Donald M. Arnold, MD MScMedical Director, Platelet Immunology Laboratory

McMaster University

Transfusion Medicine Residency TeachingJune 11, 2008

Neonatal Alloimmune Neonatal Alloimmune ThrombocytopniaThrombocytopnia

Thrombocytopenia in a fetus or neonate Thrombocytopenia in a fetus or neonate caused by maternal antiplatelet caused by maternal antiplatelet alloantibodies, directed against a fetal alloantibodies, directed against a fetal platelet alloantigen, inherited from the platelet alloantigen, inherited from the father. father.

Definition:

NeonatalNeonatalAlloimmuneAlloimmune

ThrombocytopeniaThrombocytopenia

Most common cause of Most common cause of severe TCPsevere TCP in infant in infant Most common cause of Most common cause of ICHICH in term in term

newbornsnewborns First pregnancies, First pregnancies, without warningwithout warning Otherwise healthyOtherwise healthy babies babies

NATNAT Fetus inherits platelet antigens from fatherFetus inherits platelet antigens from father

Transplacental passage of fetal platelet Transplacental passage of fetal platelet antigensantigens

Mother forms IgG alloAbs that cross placentaMother forms IgG alloAbs that cross placenta

Maternal alloAb react with fetal plateletsMaternal alloAb react with fetal platelets

AlloAb-sensitized platelets are cleared in RE AlloAb-sensitized platelets are cleared in RE systemsystem

NAT and HDNNAT and HDNNAT HDN

Affected cells

Most common antigen

Affected pregnancy

Timing of sensitization

Affected Infant

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen

Affected pregnancy

Timing of sensitization

Affected Infant

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy

Timing of sensitization

Affected Infant

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization

Affected Infant

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus ICH Hydrops fetalis

Main risk factor

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus ICH Hydrops fetalis

Main risk factor Previously affected infant Rh-negative mothers

Treatment

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus ICH Hydrops fetalis

Main risk factor Previously affected infant Rh-negative mothers

Treatment Supportive Supportive

Prevention

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus ICH Hydrops fetalis

Main risk factor Previously affected infant Rh-negative mothers

Treatment Supportive Supportive

Prevention IVIG Anti-D

Efficacy of prevention

NAT and HDNNAT and HDNNAT HDN

Affected cells Platelets Red blood cells

Most common antigen HPA-1a Rh-D

Affected pregnancy First Second +

Timing of sensitization 16 weeks onwards At birth, or during a procedure

Affected Infant TCP, bleeding Hemolysis, jaundice, kernicterus

Affected fetus ICH Hydrops fetalis

Main risk factor Previously affected infant Rh-negative mothers

Treatment Supportive Supportive

Prevention IVIG Anti-D

Efficacy of prevention ? 99%

Incidence: 1 in 1,000 to 1 in 2,000 births

NN IncidenceIncidence

Burrows and KeltonBurrows and Kelton, 1993, 1993 15,93215,932 1 in 1,7001 in 1,700

UhrynowskaUhrynowska, 2000, 2000 24,10124,101 1 in 2,4001 in 2,400

Turner,Turner, 2005 2005 26,00026,000 1 in 5,0001 in 5,000

Kjeldsen-Kragh,Kjeldsen-Kragh, 2007 2007 100,448100,448 1 in 1,7001 in 1,700

NATNAT

<150,000 - 1 in 100<150,000 - 1 in 100 < 50,000 - 1 in 400< 50,000 - 1 in 400 <20,000 - NAT<20,000 - NAT

Severity of Severity of thrombocytopenia thrombocytopenia

Burrows, Kelton 1993

Predictors of Severity of Predictors of Severity of NATNAT

• History of NAT in a siblingHistory of NAT in a sibling Murphy, Murphy, 20062006

• Worse with subsequent pregnancies Worse with subsequent pregnancies Bussel, Bussel, 19971997

• Worse with increased gestational ageWorse with increased gestational age Kaplan, Kaplan, 19881988

• ICH in a previous sibling – greater severityICH in a previous sibling – greater severityBussel, 1997Bussel, 1997

Treatment of affected Treatment of affected neonatesneonates

Without warningWithout warning Prompt recognitionPrompt recognition IVIg (2g/kg); Effective in 75% of IVIg (2g/kg); Effective in 75% of

casescases Platelet transfusions:Platelet transfusions:

Antigen-negative (maternal) Antigen-negative (maternal) plateletsplatelets

Random-donor plateletsRandom-donor platelets

= unmatched PLTs; = matched PLT; ∆ = IVIg; □= steroids

Kiefel Blood, 2006

Antenatal treatment Antenatal treatment (prevention)(prevention)

IVIg 1g/kg/wk (2g/kg/wk for refractory)IVIg 1g/kg/wk (2g/kg/wk for refractory) IVIg + corticosteroidsIVIg + corticosteroids Intrauterine platelet transfusionsIntrauterine platelet transfusions Fetal blood sampling (FBS)Fetal blood sampling (FBS)

High Risk (n= 40) Standard Risk (n= 39)

(previous ICH or PLT<20) (neither)

IVIg vs. IVIg + pred IVIg vs. pred

(1g/kg/wk) (1mg/kg) (1g/kg/wk) (0.5mg/kg)

PUBS (20 wks, repeat 3-8 wks)

Outcome: increase in fetal platelet count

Berkowitz, Bussel, 2006

Risk-based treatmentRisk-based treatment

HIGH RISK MothersHIGH RISK Mothers(platelet count)(platelet count)

PrePre 2-8 wks2-8 wks BirthBirth

IVIg alone*IVIg alone* 7,0007,000 17,00017,00067,00067,000

IVIg + pred IVIg + pred 8,0008,000 67,00067,00099,00099,000

* One ICH* One ICH Berkowitz, Bussel, 2006

Risk-based treatmentRisk-based treatment

STANDARD RISK Mothers*STANDARD RISK Mothers*(platelet count)(platelet count)

PrePre 3-8 wks3-8 wks

IVIg aloneIVIg alone >20,000>20,000 31,00031,000

Pred alone Pred alone >20,000>20,000 26,00026,000

* 2 fetal deaths, 2 ICH* 2 fetal deaths, 2 ICH Berkowitz, Bussel, 2006

Risk-based treatmentRisk-based treatment

11 SERIOUS COMPLICATIONS OF 175 11 SERIOUS COMPLICATIONS OF 175 PUBS (6%)PUBS (6%)

- 1 Fetal Death - 1 Fetal Death

- 9 Emergency C-Sections (14%) - 9 Emergency C-Sections (14%)

Risk-based treatmentRisk-based treatment

Testing for NATTesting for NAT

Antigens on PlateletsAntigens on Platelets

Blood group antigens (ABO) Blood group antigens (ABO) Common antigens (HLA)Common antigens (HLA) Platelet specific antigens Platelet specific antigens

Chosen name, or name related to Chosen name, or name related to individual with antigen (Plindividual with antigen (PlA1A1,Zav, Gov).,Zav, Gov).

Current recommendation: All antigens Current recommendation: All antigens designated as HUMAN PLATELET designated as HUMAN PLATELET ANTIGENS (HPA).ANTIGENS (HPA).

Antigens numbered in order of Antigens numbered in order of discovery. discovery.

Higher frequency allele is “a”.Higher frequency allele is “a”. Example: PLA1 = HPA-1a; PLA2 = Example: PLA1 = HPA-1a; PLA2 =

HPA-1bHPA-1b

Platelet Specific AntigensPlatelet Specific Antigens

Nomenclature

To date, 22 platelet specific To date, 22 platelet specific alloantigens identified, with 6 diallelic alloantigens identified, with 6 diallelic system (HPA-1, 2, 3, 4, 5, 15). Almost system (HPA-1, 2, 3, 4, 5, 15). Almost all are associated with a all are associated with a single single nucleotide substitution.nucleotide substitution.

Platelet Specific AntigensPlatelet Specific Antigens

Major clinically important platelet antigens in NATHPA-1a PLA1HPA-5a Br-b, Zav-bHPA-5b Br-a, Zav-aHPA-15a Gov-bHPA-15b Gov-aHPA-4a (Asian population) Pen-a

Associated with up to 5% of all NATHPA-3a Bak-aHPA-2a Ko-bHPA-2b Ko-a

Implicated in NAT, but occur rarely in the populationHPA-6b Ca-a, Tu-aHPA-8b Sr-aHPA-9b Max-aHPA-13b Sit-a

Rarely implicated in NATHPA-1b PLA2HPA-3b Bak-b

Key MessageKey Message

Gene discrepancy is Gene discrepancy is notnot NAT! NAT!

““Genetic NAT” is 10 times more Genetic NAT” is 10 times more common than common than

actual NAT”.actual NAT”.

TestingTesting

Platelet PhenotypingPlatelet Phenotyping

RadioimmunoprecipitationRadioimmunoprecipitation

Phenotyping and Phenotyping and Antibody Identification Antibody Identification

Investigation of Neonatal Alloimmune Thrombocytopenia

Platelet Antigen Typing:

Genotyping – Maternal and Paternal blood samples

Genotyping – Direct and Cultured amniocytes

Phenotyping – Maternal and Paternal samples

Platelet Antibody Investigation:

Radioimmunoprecipitation

Antigen Capture ElA

Flow Cytometry

Mom: HPA-1a negDad: HPA-1a pos

Mom: Anti-1a

Phenotype, antibody Phenotype, antibody detection (RIP)detection (RIP)

Genotype (PCR)Genotype (PCR)

Genotype (SSP)