Determination of Total Galactose from Dried Blood Spots—Extensive Assay Evaluation of a CE-Marked Test-Kit

Abstract

Most newborn screening laboratories use CE-marked or FDA-approved test-kits, like in routine clinical chemistry. National regulations require only minimal evaluation from the customer, if the test-kits are used as specified by the manufacturer. The microtiter-based kit-concept is often based on the perception, that the laboratory always processes whole microtiter plates. However, in the daily routine, this is rather a rare exception, which leads to much higher costs per newborn, compared to the costs per assay in the test-kits. In addition the amount of wasted resources is quite high. Performance of the Neonatal Total Galactose kit from Perkin Elmer was tested. We have determined specificity, limit of detection (LOD), limit of quantitation (LOQ), intra and inter assay variation, recovery, stability of measuring signal and reagents. Results were also compared with the Astoria Pacific Spot Check System. In addition, we had (by chance) the opportunity to test 2 kits, which were already expired for more than 3 years. LOD was 165 - 306 μmol/L and LOQ 475 - 703 μmol/L, depending on the definition of LOD/LOQ. Mean recovery was 112.8%, intra assay CVs were 11.3, 7.3, 4.0, and 3.0, and inter assay CVs 28.7, 15.9, 7.8, and 9.3, at 220, 590, 1200, and 2060 μmol/L respectively. Reconstituted and mixed reagents must be used within some hours, and were unstable even if stored at - 20℃. However, if the reconstituted galactose substrate reagent and galactose oxidase reagent were only mixed according to the daily requirements, and the rest stored separately at -20℃, they were stable for at least 12 days. The performance of the expired test-kits did not differ from the others. The performance of the Total Galactose kit is comparable to other tests used for newborn screening. However, we could significantly reduce the costs per newborn and reduce unnecessary production of waste, by thorough validation and modification of the assay procedures.