DEFINING POLYCYTHEMIA: A REAPPRAISAL

Abstract

The first cases of neonatal polycythemia were described over 25 years ago. To date, controversy still exists as to what critical level of hematocrit (hct) should be utilized to define this syndrome. The most common definition has been a venous hct of 65% or greater. Values as low as 60% or as high as 70% have also been suggested. In addition, the relationship between polycythemia and hyperviscosity is poorly described. We re-evaluated the definition of polycythemia based on neonatal symptoms and long-term outcome at 1-2 yrs of age and evaluated the relationship between hct and viscosity. The subjects were infants referred for further screening because of high hcts. Viscosity measurements were made using the methods and standards of Gross et al. (1973). Viscosity and venous hct were coded for 225 infants. Follow-up was available on 158 (70%). Among infants studied, elevated viscosity measurements were not limited to those with venous hct of 65% or greater. Eleven percent of infants had an abnormal viscosity, although hct was less than 65%. The enrollment mechanism did not permit identification of the lowest hct at which abnormal viscosity could be found. Infants whose venous hcts were between 65 and 69% were as likely to have neonatal symptoms as infants with hcts between 60 and 64%. Infants with markedly abnormal hcts (>69%) had similar neonatal courses. Infants with symptoms in more than one organ system varied from 26-30% of each group. Similarly, outcome measurements were not different among the three groups. No evidence of long-term sequelae was found in 44-65% of the children. In conclusion, determinations of a critical level of hct does not fully account for the effects of neonatal hyperviscosity. It is also likely that additional factors influence peripheral blood flow and must be considered when attempting to predict which infants with elevated hcts will have neonatal symptoms or long-term sequelae.

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