Pathophysiology, classification, and complications of common asymptomatic thrombocytosis in newborn infants

• Published in: Clinical and experimental pediatrics Vol. 65; no. 4; pp. 182 - 187
• Main Author: Jeon, Ga Won
• Format: Journal Article
• Language: English
• Published: Korea (South) Clinical and Experimental Pediatics / Korean Pediatric Society 01.04.2022; Korean Pediatric Society; The Korean Pediatric Society; 대한소아청소년과학회
• Subjects: Anemia; Bacteria; Blood platelets; Bone marrow; Classification; Cytokines; Feedback; Gestational age; Growth factors; Infections; Inflammation; Liver; Newborn babies; newborn infant; Pathophysiology; Pediatrics; platelets; Premature babies; premature infant; Review; thrombocytosis; Thromboembolism; thrombopoietin; 소아과학; Thrombocytosis; Premature infant; Platelets; Thrombopoietin; Newborn infant
• ISSN: 2713-4148; 2713-4148
• DOI: 10.3345/cep.2021.00864

We frequently encounter newborn infants with thrombocytosis in the neonatal intensive care unit. However, neonatal thrombocytosis is not yet fully understood. Thrombocytosis is more frequently identified in newborns and young infants, notably more often in those younger than 2 years than in older children or adults. The production of megakaryocytes (megakaryopoiesis) and platelets (thrombopoiesis) is mainly regulated by thrombopoietin (TPO). Increased TPO levels during infection or inflammation can stimulate megakaryopoiesis, resulting in thrombopoiesis. TPO concentrations are higher in newborn infants than in adults. Levels increase after birth, peak on the second day after birth, and start decreasing at 1 month of age. Initial platelet counts at birth increase with gestational age. Thus, preterm infants have lower initial platelet counts at birth than late-preterm or term infants. Postnatal thrombocytosis is more frequently observed in preterm infants than in term infants. A high TPO concentration and low TPO receptor expression on platelets leading to elevated plasma-free TPO, increased sensitivity of megakaryocyte precursor cells to TPO, a decreased red blood cell count, and immaturity of platelet regulation are speculated to induce thrombocytosis in preterm infants. Thrombocytosis in newborn infants is considered a reactive process (secondary thrombocytosis) following infection, acute/chronic inflammation, or anemia. Thrombocytosis in newborn infants is benign, resolves spontaneously, and, unlike in adults, is rarely associated with hemorrhagic and thromboembolic complications.