Monitoring erythrocyte free radical resistance in neonatal blood microsamples using a peroxyl radical-mediated haemolysis test

Inadequate resistance to oxidative stress has been implicated in several diseases of premature children. Antioxidative defences at the membrane level can be studied by measuring haemolysis induced through exposure of erythrocytes to the free radical generator AAPH (2,2'-azobis (2-amidinopropane)dihydrochloride). We developed a micromodification of this haemolysis test requiring only 15 mu l of erythrocytes derived from capillary blood samples. The time needed for 50% haemolysis (T50%) was used to characterize radical resistance of erythrocytes. T50% results in adult samples were highly reproducible. T50% values in healthy term infants on the first 2 d of life were lower than in adults (p < 0.001), but increased to the same level thereafter. A correlation was found between T50% values and plasma tocopherol levels as determined in plasma of each of the capillary blood samples (p <0.001). On the first day of life T50% results in preterm infants (n = 20) were higher than in term infants (p < 0.001). It was easy to monitor T50% results and plasma tocopherol levels in preterm infants that were not at all burdened by the sampling method, almost daily over several weeks. The micromodification presented simplifies monitoring of antioxidative defences in sick preterm infants.