Chapter 92: Thrombocytopenia

INTRODUCTION

Thrombocytopenia in neonates is defined as a platelet count of less than 150 × 10⁹/L. The prevalence of thrombocytopenia in healthy term infants is 1%–2%, whereas up to 35% of neonates admitted to intensive care units may have low platelet counts.¹ There are developmental differences in megakaryopoiesis between neonates and older children. Neonatal megakaryocytes are less capable of upregulating platelet production or mounting as high a level of thrombopoietin (Tpo) when compared to adults with the same degree of thrombocytopenia.² These developmental differences account for the vulnerability of sick neonates to thrombocytopenia.

The major causes of neonatal thrombocytopenia are increased platelet consumption or decreased platelet production. However, both mechanisms can contribute to thrombocytopenia in any given patient, particularly in sick or premature neonates.

DIAGNOSIS/INDICATION

Clinical Findings: History and Physical

A detailed medical history and physical examination will guide the diagnostic approach to thrombocytopenia. Medical history and complications during pregnancy are important because many maternal factors can cause neonatal thrombocytopenia. Maternal drugs and antibodies that cross the placenta can affect an infant’s platelet count. Complications during pregnancy that result in chronic fetal hypoxia or intrauterine growth retardation (IUGR) are frequent causes of early-onset neonatal thrombocytopenia.³ Causes of chronic fetal hypoxia and IUGR include pregnancy-induced hypertension or diabetes, placental insufficiency, and placental infarction or malformation. Perinatal asphyxia is another common cause of early-onset thrombocytopenia. Family history of chronic thrombocytopenia suggests a hereditary thrombocytopenia or a genetic syndrome associated with low platelet counts; a family history of previous neonatal thrombocytopenia suggests maternal immune-mediated thrombocytopenia.

Physical findings of thrombocytopenia vary with the platelet count and the primary cause of thrombocytopenia. Many neonates are asymptomatic. However, in those who have bleeding manifestations, bruising and petechiae are the most common presenting symptoms, often noted on the face and head secondary to birth trauma. Thrombocytopenia commonly is associated with mucocutaneous bleeding. Bleeding also can occur with trauma following phlebotomy, after intramuscular injections (prophylactic vitamin K or hepatitis vaccine), umbilical stump bleeding, or associated with circumcision. Intra-abdominal bleeding and intracranial hemorrhage (ICH) generally occur only in severe thrombocytopenia (platelet count less than 50 × 10⁹/L). A bulging fontanel, seizures, or other neurologic signs in a thrombocytopenic neonate warrant urgent radiographic evaluation for an intracranial bleed. Sick infants in the intensive care unit also may have bleeding from intravenous sites, surgical sites, or endotracheal tubes.

Confirmatory/Baseline Tests

When a low platelet count is suspected, a complete blood cell count (CBC) with a review of the peripheral blood smear should be done. The diagnostic approach to multilineage cytopenias is different from that for isolated thrombocytopenia. The morphology of platelets as well as red and white blood cells (WBCs) may provide clues to diagnosis. For example, the presence of WBC inclusions and large platelets suggests a hereditary macrothrombocytopenia, ...