Thrombocytopenia in neonates

Please note that some guidelines may be past their review date. The review process is currently paused. It is recommended that you also refer to more contemporaneous evidence.

A well infant who presents unexpectedly on the first day of life with extensive bruising and/or a petechial rash and who is found to have isolated thrombocytopenia (platelet count <100 x 109/L) without an obvious cause must be presumed to have neonatal alloimmune thrombocytopenia until proven otherwise.

Thrombocytopenia (TP) in the newborn is defined as a platelet count less than 150 x 109/L. This occurs in 1-4 per cent of all newborn babies.

Points to note about thrombocytopenia:

• The majority of episodes of TP present during the first 72 hours of life.
• The highest incidence of TP is in sick, preterm babies (40-70 per cent).
• Thrombocytopenia is the most common haematological abnormality in the NICU. Nearly 25 per cent of sick infants develop TP, which is trivial for some infants with a platelet count of 100-150 x 109/L.
• 50 per cent or more of affected infants, platelet counts fall below 100 x 109/L.
• 20 per cent of infants have platelet counts < 50 x 109/L.
• Automated platelet counts may be abnormally low due to platelet aggregation in the sample.
• Confirm low results by blood film examination and often a repeat sample (arterial or venous) is needed.

Because the most likely cause of severe TP in a baby remaining in a special care nursery (SCN) is neonatal alloimmune thrombocytopenia (NAITP), special attention is given to this condition.

NAIT is often referred to as fetomaternal alloimmune thrombocytopenia (FMAIT).

Differential diagnosis of thrombocytopenia in babies by age at presentation

Fetal

• neonatal alloimmune TP (NAITP)
• maternal autoimmune disease idiopathic thrombocytopenia purpura (ITP), SLE
• congenital infections CMV, toxoplasmosis, rubella
• severe rhesus disease
• chromosomal disorders trisomy 21, 18, 13
• rare inherited disorders TAR - TP with absent radii

Neonate < 72 hours of age

• placental insufficiency PET, IUGR, diabetes
• birth asphyxia
• perinatal infection GBS, E. coli, haemophilus influenza listeria
• congenital infection CMV, toxoplasmosis, rubella
• NAITP
• maternal autoimmune disease ITP, SLE
• thrombosis renal vein, aortic
• rare inherited disorders TAR, Wiskott-Aldrich syndrome, congenital amegakaryocytic thrombocytopenia (CAMT)

Neonate > 72 hours of age

• bacterial infection (nosocomial)
• infected indwelling lines
• NEC
• maternal autoimmune disorders ITP, SLE
• congenital infection CMV, toxoplasmosis, rubella
• rare inherited disorders TAR, Wiskott-Aldrich syndrome

Neonatal alloimmune thrombocytopenia (NAITP)

Issues to note about NAITP:

• NAITP is sometimes known as isoimmune thrombocytopenia and results from sensitisation of the mother to antigens present on fetal platelets.
• In contrast to Rh alloimmunisation, 40-60 per cent cases occur in a first born.
• 75-90% of subsequent pregnancies are affected.
• Severe cases in fetus or newborn occur in one in 1,200 pregnancies.
• If NAITP is untreated, intracranial haemorrhage occurs in 10-30 per cent of cases.
• Overall fetal and neonatal mortality in 6-13 per cent of cases.
• Long-term neurodevelopmental sequelae in 20-25 per cent of survivors.
• Diagnosed by demonstration of fetomaternal incompatibility for a platelet surface antigen and presence of maternal platelet alloantibodies that react with a 'foreign' antigen present on platelets of the infant and father but not the mother's platelets.
• Suspect NAIT in a thrombocytopenic newborn that is otherwise well, normal maternal platelets and no history of maternal autoimmune disease.
• All children with suspected or proven NAITP warrant a cranial ultrasound to exclude intracranial haemorrhage.