Rapid measurement of creatine, creatinine, and guanidinoacetate from dried blood spots: a possible screening assay for guanidinoacetate methyltransferase (GAMT) deficiency

Newborn screening for X-linked adrenoleukodystrophy utilizes tandem mass spectrometry to analyze dried-blood spot specimens. Quality control materials (dried-blood spots enriched with hexacosanoyl lysophosphatidylcholine) were prepared and stored at different temperatures for up to 518 days to evaluate the stability of this biomarker for X-linked adrenoleukodystrophy.Dried-blood spot storage included desiccant (45, 171, and 518 days) or omitted desiccant (53 days at > 90% relative humidity). Specimens were stored for 171 and 518 days at − 20 °C, 4 °C, ambient temperature, and 37 °C. Each weekday for 45 days, a bag of specimens stored at 4 °C was warmed to ambient temperature and one specimen was removed for storage at − 80 °C. Specimens were analyzed by high-performance liquid-chromatography electrospray ionization tandem mass spectrometry and data was plotted as concentration (micromoles per liter) vs. time. Linear regression provided slope and y-intercept values for each storage condition.Small slope values (0.01 or less) and y-intercept values close to the enrichment indicated less than 11% loss of hexacosanoyl lysophosphatidylcholine under all storage conditions tested.Quality control materials for X-linked adrenoleukodystrophy are stable for at least 1 year when stored with desiccant.