A newborn, healthy, full term, male child, was born with bruising on his left thigh and developed petechiae and purpuric hemorrhages several hours after birth. The baby was moved to the NICU for observation and a CBC was ordered by the NICU provider.
- WBC, RBC, Hgb, Hct and indicies were normal
- Platelet count 58 x103/μL
- Baby exhibited no symptoms of sepsis
- Smear reviewed with no platelet clumping observed
The mother is a 28 year old, gravida 1, para 1 with normal CBC and platelet count. Her prenatal history was unremarkable. She has no history of immune thrombocytopenia (ITP) and no history of being prescribed drugs known to be associated with drug induced thrombocytopenia
Thrombocytopenia is not an uncommon finding in neonates, particularly in the neonatal intensive care unit (NICU). In preterm infants, the most common causes of thrombocytopenia are complications of pregnancy, including pregnancy-induced hypertension (PIH), intrauterine growth retardation, preeclampsia ,and HELLP syndrome (hemolytic anemia, elevated liver enzymes, low platelet count). Examination of a peripheral smear in these patients will typically reveal neutropenia with densely packed red cells, increased nucleated RBCs and deceased platelet estimate. These placental insufficiency cases typically occur within the first 72 hours of life, platelet counts are >50 x 103/μL, resolve without treatment and require no further investigation. On the other hand, thrombocytopenia in preterm infants that develops after 72 hours is most likely due to sepsis or necrotizing enterocolitis and requires investigation and treatment.2
In an otherwise healthy appearing full term infant, the most common cause of thrombocytopenia in the first 72 hours of life is neonatal alloimmune thrombocytopenia (NAIT). When a platelet count drops below 150 x 103/L in these newborns, it is important to investigate the thrombocytopenia. The first step is to always check a peripheral smear for clumping to rule out spurious thrombocytopenia. With a low platelet count and the absence of spurious thrombocytopenia, NAIT can be suspected. This condition is similar in pathogenesis to hemolytic disease of the fetus and newborn (HDFN), and is caused by an incompatibility in human platelet antigens between mother and baby. In about 80% of cases, the mother is found to be HPA-1b and the father and baby are HPA-1a.1 The mother forms anti-HPA-1a which crosses the placenta and destroys the fetus’ platelets. Most cases of NAIT are asymptomatic, or cause only mild bleeding, and resolve in 1-2 weeks.1
Although many cases of NAIT are mild, it is important to recognize because it can be a life-threatening disorder. With more severe thrombocytopenia, in both premature and full term infants, NAIT can result in intracranial bleeding either before birth or shortly after birth. NAIT can also cause long term neurologic complications. Therefore, when a neonate is suspected to have NAIT, he should be screened for intracranial hemorrhage. Since mothers are most often found to have anti- HPA-1a, and the second most commonly found antibody is anti-HPA-5b, neonates with platelet counts <30 x 103/L should be transfused with antigen matched or HPA-1a and HPA-5b negative, CMV negative, single donor apheresis platelets.
It is important to note that NAIT can occur in a first pregnancy but subsequent pregnancies are usually more severely affected. In confirming NAIT after a first delivery or monitoring a subsequent pregnancy, serological testing should be done on both parents to determine the risk of having an infant born with NAIT. If the father is homozygous for the antigen which the mother lacks, 100% of infants would be at risk. If the father is heterozygous, an infant would have a 50% chance of inheriting the antigen from the father.
NAIT in a first pregnancy is typically unrecognized until after birth. Some groups have advocated for routine prenatal screening for NAIT in all pregnant women, but this is costly and still debated. It is agreed that after an affected first child, subsequent pregnancies should be monitored closely. In at risk pregnancies, weekly antenatal IVIg infusions should be used during pregnancy to help prevent fetal bleeding.3
The mother in this case was tested and found to be HPA-1a negative with anti-HPA-1a. The father was also tested and found to be HPA-1a positive. The infant’s platelet counts began to increase at 7 days, with no further bleeding. The mother was referred to a NAIT specialty team for future pregnancies.
Diagnosis: Neonatal Immune Thrombocytopenia (NAIT)
- Similar in pathogenesis to hemolytic disease of the fetus and newborn (HDFN)
- Incompatibility in human platelet antigens between mother and baby.
- Can affect first born
- In majority of cases, the mother is HPA-1b and the father and baby are HPA-1a
- Second most common is anti-HPA-5b
References
- http://naitbabies.org/wp-content/uploads/141208_NAIT_Registry_poster.pdf
- Subarna Chakravorty and Irene Roberts. How I manage neonatal thrombocytopenia . Blackwell Publishing Ltd, British Journal of Haematology. 2011; 156, 155–162
- T.W. de Vos, D. Winkelhorst, M. de Haas, E. Lopriore, D. Oepkes. Epidemiology and management of fetal and neonatal alloimmune thrombocytopenia. Transfusion and Apheresis Science. 2020
- Shamudheen Rafiyath, Immune Thrombocytopenia and Pregnancy Treatment & Management Updated: Sept. 2020 https://emedicine.medscape.com/article/208697-treatment
-Becky Socha, MS, MLS(ASCP)CM BB CM graduated from Merrimack College in N. Andover, Massachusetts with a BS in Medical Technology and completed her MS in Clinical Laboratory Sciences at the University of Massachusetts, Lowell. She has worked as a Medical Technologist for over 30 years. She’s worked in all areas of the clinical laboratory, but has a special interest in Hematology and Blood Banking. When she’s not busy being a mad scientist, she can be found outside riding her bicycle.
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