Haematocrit values and blood viscosity in the newborn infant

The haematocrit values in 51 babies were studied to observe the possible variations due to the method and time of sampling and to relate these findings to blood viscosity. A good correlation (r = 0,9536) between haematocrit values of warmed heel capillary blood and of central venous samples was found. Prediction of venous value from a known sample of capillary blood can be made using regression lines and 95% confidence limits. The correlation between venous and unwarmed blood samples from the heel is not as good. A central venous haematocrit value of 65% or greater gave a 100% risk of the infant's blood being hyperviscous. Hyperviscosity occurred in 71% of infants with a capillary haematocrit value of 65 - 68% but the figure rose to 81% when the peripheral haematocrit value was 68% or more.