Low platelet count in an otherwise
healthy term newborn is due to NAIT until proven otherwise.
Urgent matched platelet transfusion
should be discussed with specialist on call at all times.
Neonatal Alloimmune Thrombocytopenia (NAIT) results from maternal human
platelet antibodies (HPA) against fetal platelet antigens inherited from the
father. In contrast to rhesus haemolytic disease, platelet allo-immunization
can occur during the first pregnancy.
NAIT presents commonly in the newborn with unexpected bruising and
purpura or can be the cause of severe intracranial haemorrhage.
The possibility of allo-immunization during pregnancy is particularly
high for HPA-1a, -5b and -15b among Europeans, for HPA-2b and HPA-3a among
Maori, for HPA -4b among Asians, and for HPA-6b among Polynesians. The
picture becomes more complex for families with mixed ethnic backgrounds.(1)
The incidence of NAIT is reported to be between 1:800 and 1:1000. In
clinically presenting cases, the rate of intracranial haemorrhage is ~20%
followed by death in 10% and neurological sequelae in 20% of these newborns.(2)
The commonest mode of presentation is the well neonate with bruises or
petechiae, but the spectrum of disease ranges from sub-clinical moderate
thrombocytopenia to catastrophic intracranial haemorrhage and death. A high
index of suspicion is essential in all cases of active bleeding, but also in
asymptomatic laboratory diagnosed thrombocytopenia. A history of
thrombocytopenia in a previous sibling makes the diagnosis almost certain.
Excessive haematoma at injection site
Previously affected sibling
Recurrent fetal loss and stillbirth
Postnatal ICH (e.g.: silent, full
SHOULD NOT DELAY PLATELET TRANSFUSION IF REQUIRED URGENTLY(2)
FBC to confirm platelet count
If no paternal blood available or paternity is uncertain, send 1 x
infant EDTA (purple, 1 mL) tube for genotyping.
FBC: normal platelet count during pregnancy
4 x CPDA (yellow) tubes for genotyping and 1x plain (red) tubes for
4 x CPDA (yellow) tubes for genotyping.
If platelet transfusion is needed, ring haematologist on call to
Definitive diagnosis of NAIT depends on parental testing.
Ideally, matching with maternal antibodies is preferred prior to
Phone laboratory with specimen queries (523 5731).
Transfuse if any bleeding or high risk
Transfuse if major bleeding
Do not transfuse
If transfusion is needed, discuss the case with a clinical
Urgent transfusion of 10 mL/kg of platelets (over 30-60 min) is needed
if the infant is bleeding or at high risk of bleeding. Infants are at
significant risk for ICH in the first days of life.
Matched platelets are first choice, but may not be available in a timely
If matched platelets are not available in a timely fashion, unmatched
platelets (consider addition of IvIg) should be given.
Consider IvIg (1-2 g/kg) in combination with unmatched platelets if
matched platelets are not available in a timely fashion.(5)
IvIg as stand-alone treatment may be considered, but response can be
delayed by 24-36 hours, leaving a window of risk for ICH.
Ensure Vitamin K has been administered
Urgent head ultrasound
Infants are at significant risk of ICH in the first days of life.
If the platelet count fails to rise in response to matched platelets
consider alternative diagnoses, and check for rarer maternal antibody types.
Affected infants should have a FBC checked daily until platelet count is
stable over 100x109/L.
Maternal antibody levels fall towards term, so repeat testing 6 weeks
post-partum is required in some cases.
It is essential that parental investigation is initiated prior to
discharge and adequate follow up arrangements made.
The risk of a subsequent pregnancy being affected is 100% if the father
is homozygous for the reacting antigen, and 50% if heterozygous.
In general, subsequent pregnancies are at least as severely affected as
the first. Antenatal therapy in subsequent pregnancies remains contentious,
but options include intrauterine platelet transfusion, maternal
immunoglobulin and steroids.(5) If NAIT is confirmed, future
pregnancies should by managed by the Maternal Fetal Medicine Team.
Bakchoul T, Bassler D, Heckmann M, Thiele T,
Kiefel V, Gross I, et al. Management of infants born with severe neonatal
alloimmune thrombocytopenia: the role of platelet transfusions and
intravenous immunoglobulin. Transfusion. 2014;54:640–5.
Kaplan C. Foetal and neonatal alloimmune
thrombocytopaenia. Orphanet J Rare Dis. 2006 Jan;1:39.
Roberts I, Murray N a. Neonatal
thrombocytopenia. Semin Fetal Neonatal Med. 2008;13:256–64.
Edinur H a, Dunn PPJ, Lea R a, Chambers GK.
Human platelet antigens frequencies in Maori and Polynesian populations.
Transfus Med. 2013;23:330-7
Transfusion Medicine Handbook. 2008;New Zealand
Blood Service, www.nzblood.co.nz