- 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) is
a disorder caused by fetomaternal platelet incompatibility analogous to that
in Rhesus Haemolytic Disease, with maternal anti-platelet antibodies
crossing the placenta and destroying fetal platelets.
- The majority of cases are caused by antibodies
directed against Human Platelet Antigen-1a (HPA-1a) and HPA-5b, but many
rarer reactions have been reported.
- Prospective studies have shown incidence to be
1:1,100 live births,1 but the condition is under-reported.2
- Mortality is around 10% of presenting cases,
with neurological sequelae, including intracranial haemorrhage and
subsequent neurodevelopmental delay in up to 25%.3
The commonest mode of presentation is probably
the well neonate with bruises or petechiae. However the spectrum of
disease ranges from sub-clinical moderate thrombocytopenia to catastrophic
intracranial hemorrhage (ICH) 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.
- Previously affected sibling
- Recurrent fetal loss
- Antenatal ICH/hydrocephalus
- Bruising/bleeding neonate
- Excessive haematoma at injection site
- Disseminated intravascular coagulopathy
- Postnatal ICH (silent or presenting with
Also see Neonatal
- Placental insufficiency
- Congenital infection
- Artefact - clotted FBC sample
- Autoimmune thrombocytopenia (maternal ITP)
||to confirm platelet
||likely to have been
performed during pregnancy. Maternal platelet count is normal in NAIT.
- Definitive diagnosis of NAIT depends on
- In most cases the lab prefers to do this prior to
platelet transfusion, but discussion with haematologist on call is
necessary to arrange urgent testing.
- FURTHER TESTING SHOULD NOT DELAY PLATELET TRANSFUSION IF REQUIRED URGENTLY
||3 x CPD (yellow)
and 1x plain (red) tubes for anti-platelet antibodies and genotyping.
||3 x CPD (yellow)
tubes for genotyping.
If no paternal blood available, send 1 x CPD (yellow) tube for platelet
- Direct crossmatch between parents will also be
Maternal antibody levels fall towards term, so
repeat testing 6 weeks post-partum is required in some cases.
- Phone laboratory with specimen queries (523
Transfuse if any bleeding
Transfuse if major bleeding
Do not transfuse
- If the infantís platelet count is <30x109/L
and the maternal count is normal, the treatment of choice is urgent
transfusion of 10ml/kg of matched platelets.
In most cases these will be HPA-1a
negative, but Maori and Asian mothers are more likely to have antibodies
other than anti HPA-1a.
- Infuse platelets over 30-60 minutes (see
platelet protocol), and recheck platelet count after one hour.
Antigen-negative platelets should be given
urgently, as infants are at significant risk of ICH in the first days of
- If antigen negative platelets are not
available, intravenous immunoglobulin (IVIG) 1g/kg/day for 2 days may be effective.
There is often a delay of 24-48 hours
prior to response, leaving a window of risk for ICH.
- 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. Need for
platelet transfusion at moderately low platelet counts (30-100 x 109/L) is
- It is essential that
parental investigation is initiated prior to discharge and adequate follow up
The risk of a subsequent pregnancy being affected is 100%
if the father is homozygous for the reacting antigen, and 50% if
- 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
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L.M., et al., The natural history of fetomaternal alloimmunization to the
platelet-specific antigen HPA-1a (PlA1, Zwa) as determined by antenatal
screening. Blood, 1998. 92(7): p. 2280-7.
M.F., S. Verjee, and M. Greaves, Inadequacies in the postnatal management
of fetomaternal alloimmune thrombocytopenia (FMAIT). Br J Haematol, 1999.
105(1): p. 123-6.
of alloimmune neonatal thrombocytopenia. Lancet, 1989. 1(8630): p. 137-8.
J.B., et al., Fetal alloimmune thrombocytopenia. N Engl J Med, 1997.
337(1): p. 22-6.
I.A. and N.A. Murray, Thrombocytopenia in the newborn. Curr Opin Pediatr,
2003. 15(1): p. 17-23.