Thrombocytopenia

Definition

  • Platelet count <150,000 in a neonate

Background

  • Fetuses begin making platelets 5 days post conception and reach adult levels by 22w gestation
    • For this reason, the definition of thrombocytopenia has the same parameters as adults
    • Platelet counts increase with increasing postnatal age
    • Recent studies questioning the validity of using adult parameters for neonates, but no change in definition yet
  • Normal term neonates have incidence of thrombocytopenia <1% while the incidence for NICU admits is 18-35%
  • Most cases are mild and resolve within 7-14 days, but a small subset of cases (2.5-5%) are severe and take months to resolve
  • Severe, persistent, and symptomatic patients must be evaluated

Etiology

  • Increased Platelet Destruction
    • Alloimmune thrombocytopenia: maternal ab against fetal platelets
      • Neonatal Alloimmune Thrombocytopenic Purpura (NATP): fetal platelets contain an antigen inherited from the father that the mother lacks. Mother makes IgG against the paternal antigen which crosses the placenta and causes thrombocytopenia
      • Infants are at risk for intracranial hemorrhage. 25-50% occur in utero
    • Autoimmune thrombocytopenia: maternal ab against maternal and fetal platelets
      • SLE, ITP: maternal ab against maternal and fetal platelets
      • Drug-related: maternal or fetal ab
      • antiepileptics, quinidine, PCN, heparin, hydralazine, thiazides
    • Peripheral Consumption
      • Hypersplenism
      • Kasabach-Merritt Syndrome: DIC with capillary hemangiomas
      • DIC
      • Infection: bacterial, viral, or fungal.
      • Necrotizing enterocolitis
      • Thrombosis
      • Hemorrhage (most IVH, pulm, or GI)
      • premature IVH: normal platelet counts at time of bleed, so causal relationship difficult to determine
      • term IVH: thrombocytopenia common at time of bleed
  • Decreased Platelet Production
    • Genetic Disorders     
      • Thrombocytopenia-absent radius syndrome: AR, bilateral absent radii, thumbs present
      • Fanconi’s Anemia
      • Congenital amagakaryocytic thrombocytopenia
      • Chromosome abnormalities: trisomies (21, 18, 13), Turner syndrome
      • Congenital platelet disorders: Wiskott-Aldrich, May-Hegglin, Bernard-Soulier, Alport
    • Infiltrative Disorders: neoplasms. Rare in the neonatal period.
    • Toxic injury to megakaryocytes by infections/drugs
  • Miscellaneous Causes
    • Neonatal Cold injury: mechanism unclear
    • Asphyxia: mechanism unclear, but possibly related to hypoxic injury
    • Von Willebrand Disease: platelet aggregation
    • Preeclampsia: nadir at 2-4 days with resolution typically by 7-10 days
    • Dilution

Management

  • Initial evaluation
    • Thorough history and physical exam of mother and neonate, including birth history
      • Healthy appearing infant more likely to have congenital/immunologic mediated cause
      • Ill appearing infant more likely to have infection, DIC, NEC, asphyxia as cause
    • Labs:
      • Neonate: CBC (repeated to confirm thrombocytopenia), platelet ag typing, peripheral smear, coags, sepsis work up if ill appearing, eval for congenital infection, genetic testing
      • Maternal: CBC (repeated to confirm thrombocytopenia if present), platelet ag typing
    • Cranial US to evaluate for IVH. If present, low threshold for transfusion. Repeat prior to discharge
  • Treatment
    • If underlying cause known (mom with SLE, ITP, known infection, etc), treat.
    • Platelet counts should be more aggressively maintained for first 72-96 hours of life as risk for IVH highest in this time period. If no IVH, then clinical situation used to guide need for transfusion
      • High dose IVIG for 3-4 days is used as adjunct
      • Methylprednisolone used only in emergency situations as evidence lacking
    • When to transfuse?
      • No clear guidelines
      • Term infant, healthy, no other risks for hemorrhage: typically if <30,000
      • Preterm, ill, or with other risk factors: typically if <50,000
      • Benefit of platelet transfusion not clearly established; some recent suggestion that transfusion may be harmful
    • Other therapies
      • IVIG, steroids, exchange transfusion typically used for immune mediated causes
      • Current research into using thrombopoeitic mimetics as an alternative to transfusion

References

  1. Murphy S. Consultation with the Specialist. Thrombocytopenia. Pediatrics in Review. Feb 1999; 20(2): 64-68.
  2. Albert TS. Throbopoietin in the Thrombocytopenic Term and Preterm Newborn. Pediatrics. June 2000; 105(6): 1286-1291.
  3. Silver RM. Neonatal Alloimmune Thrombocytopenia: Antenatal Management. American Journal of Obstetrics and Gynecology. May 2000; 182(5): 1233-1238.
  4. Behrman: Nelson Textbook of Pediatrics, 16th ed (2002). Philadelphia: W.B. Saunders Company.
  5. Gomella: Neonatology: Management, Procedures, On-Call Problems, Diseases and Drugs, 4th ed (1999). McGraw-Hill/Appleton and Lange.
  6. Ferrar-Marin F, et al. Neonatal Thrombocytopenia and Magakaryocytopoeisis. Seminar in Hematology. July 2010; 47 (3) 281-288
  7. UpToDate. Neonatal Thrombocytopenia.

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