Introduction

Polycythemia of the newborn is first mentioned in the Bible as Esau and Jacob are described at the time of their birth. Esau appears to be the recipient of a twin-to-twin transfusion (Genesis 25 : 25: “The first one emerged red …”). There is little in the modern medical literature concerning polycythemia in the newborn until the early 1970s (1–5). During this time, there were a number of case reports and small series of infants with various symptoms that were thought to be secondary to an elevated hematocrit and blood viscosity. It was not until the 1980s that several investigators systematically examined the association between polycythemia, hyperviscosity of the blood, and organ-system dysfunction. These studies have done much to enlighten our understanding of the relationships between abnormalities of the hematocrit, blood viscosity, organ blood flow, and organ function. The dissemination of this knowledge has provided a clinical approach that is based on well-defined data and has clarified the role of polycythemia as an etiologic factor for organ dysfunction in the neonate.

Definitions

Definitions of polycythemia and hyperviscosity have varied by study and methodology. Common variables have been the source of the blood sample and the age of the infant at the time of measurement (6–11). In many studies, a hematocrit value of 65% or above has been diagnostic for polycythemia. Using cord blood from appropriate-for-gestational-age (AGA) infants, Gross and colleagues defined hyperviscosity as a value that was two standard deviations greater than the mean (Fig. 9.1) (5). Using blood samples from three different sites (peripheral vein, umbilical vein, and capillary), Ramamurthy and Brans defined hyperviscosity as a value that was three standard deviations from the mean (6). This coincided with an umbilical venous hematocrit value of 63% or above. This study also found that capillary samples were higher than those from the peripheral vein, which in turn were greater than those from the umbilical vein.