Agreement between capillary and arterial serum gentamicin concentrations in neonates

Due to inherent difficulties in blood sampling in neonates, specimens for laboratory analyses are often obtained by heel puncture technique. While agreement between venous or arterial and capillary concentrations of some substances has been reported, that for gentamicin, when obtained by heel stick, has not. Simultaneously obtained heel stick (capillary) and umbilical artery (arterial) serum samples were analyzed for gentamicin concentrations in 20 preterm neonates. Further, 14 subjects underwent manual manipulation of the heel to encourage blood flow before sampling to test the effect of such manipulation on gentamicin concentration. The agreement between capillary and arterial serum concentrations of gentamicin was found to be excellent in infants greater than 1000 g body weight. Manipulation of the heel had no effect on this agreement.