Galactose-1-phosphate uridyltransferase dried blood spot quality control materials for newborn screening tests

Abstract

ObjectivesWe aimed to prepare dried-blood-spot (DBS) quality control (QC) materials for galactose-1-phosphate uridyltransferase (GALT), to evaluate their stability during storage and use, and to evaluate their performance in five DBS GALT test methods. Design and methodsWe prepared and characterized GALT-normal and GALT-deficient DBS materials and compared GALT activities in DBSs after predetermined storage intervals at controlled temperatures and humidities. External evaluators documented the suitability of the DBS QC materials for use in five GALT test methods. ResultsGALT activity losses from DBSs stored in low (<30%) humidity for 14days at 45°C, 35days at 37°C, 91days at room temperature, 182days at 4°C, and 367days at −20°C were 54%, 53%, 52% 23%, and 7% respectively. In paired DBSs stored in high humidity (>50%) for identical intervals, losses were: 45°C—68%; 37°C—79%; room temperature—72%, and 4°C—63%. GALT activities in DBSs stored at 4°C were stable throughout 19 excursions to room temperature. Twenty-five of 26 external evaluators, using five different GALT test methods, classified the GALT-deficient DBSs as “outside normal limits”. All evaluators classified the GALT-normal DBSs as “within normal limits”. ConclusionsMost of the GALT activity loss from DBSs stored at elevated or room temperature was attributable to the effects of storage temperature. Most of the loss from DBSs stored at 4°C was attributable to the effects of elevated humidity. Loss from DBSs stored at −20°C was insignificant. The DBS materials were suitable for monitoring performance of all five GALT test methods.