Polycythaemia neonatorum

**Definition:** Polycythaemia of the neonate represents an excessive quality of circulating red blood cells due to excessive marrow production and haematocrits that exceed ~60%.

**Long definition:** Polycythemia of the neonate represents an excessive qualtity of circulating red blood cells due to excessive marrow production and hematocrits that exceed ~60%. Polycythemia can or cannot be associated with hyperviscosity and may or may not be symptomatic.