Differential diagnosis and management of polycythemia

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Defining polycythemia and hyperviscosity

The terms neonatal polycythemia and hyperviscosity are often used interchangeably. Though this is not accurate, it represents an understandable simplification. In many cases, infants who have hyperviscosity are polycythemic, and vice versa [1], [2]. Nonetheless, polycythemia refers to an abnormal increase in red cell mass (hematocrit), whereas hyperviscosity refers to an increase in the internal friction of blood or the force required to achieve flow. The viscosity of whole blood is affected by

Polycythemia

The multiplicity of definitions used in the literature to define polycythemia has complicated the discussion of the incidence and outcome of this condition. The most widely accepted definition is a venous hematocrit of 65% or greater. Still, variability in sampling site, timing, and technique determine the incidence and perhaps the outcome of infants who have polycythemia/hyperviscosity. Studies have suggested that the hematocrit at term will rise from cord blood levels to a peak at 2 hours of

Incidence of neonatal polycythemia and hyperviscosity

The incidence of neonatal polycythemia and hyperviscosity ranges from 1% to 5% in the total newborn population (Table 2) [1], [13], [14], [15], [16], [17]. It is also influenced by birth weight, gestational age, and altitude. Infants who are small or large for gestational age and infants born at high altitudes have a higher incidence of polycythemia. Premature infants, especially those born after less than 34 weeks' gestation, rarely have polycythemia or hyperviscosity.

Conditions that predispose to the development of neonatal polychythemia

Erythropoiesis in the human fetus is acclimated to the relatively hypoxic fetal environment. Compared with older infants and children, fetal hematocrit is elevated and allows for an increased oxygen carrying capacity. Factors that interfere with placental oxygen concentration may increase fetal hematocrit even further, resulting in a pathologically high neonatal red cell mass. Examples include high altitude [1], maternal diabetes [18], hypertension [19], intrauterine growth retardation [20],

Clinical features and complications

Infants who have polycythemia often show increased whole blood viscosity. As the hematocrit rises above 65%, there may be an increased tendency for diminished blood flow, especially in the cerebral, hepatic, renal, and mesenteric microcirculations. Clinical symptoms may include lethargy, cyanosis, respiratory distress, jitteriness, hypotonia, feeding intolerance, hypoglycemia, and hyperbilirubinemia. Symptoms are outlined in Box 2. Several organ systems may be involved.

Treatment

Treatment of neonatal polycythemia and hyperviscosity remains controversial. Although partial exchange transfusion is recommended for symptomatic infants, outcome data do not show clear long-term benefits. Undoubtedly, infants who have clinical manifestations should receive care aimed at alleviating their symptoms. The debate lies in whether this care should involve symptomatic therapy or routine partial exchange transfusion (PET) to replace the infant's blood with a plasma substitute.

Prognosis

The diversity of follow-up data on neonatal polycythemia suggests that the outcome of these infants is variable. In part, this may result from other associated conditions, the severity of these conditions, and their underlying etiology. Still, the diagnosis of polycythemia raises many questions and concerns. For example, which infants will develop symptoms, how should they be treated, and what care will improve their short- and long-term outcomes? Polycythemia/hyperviscosity is an intriguing

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