Measurement of the absolute concentration of the biomarker psychosine in dried blood spots (DBS) is useful for diagnosis and prognosis of Krabbe disease and to support newborn screening of this leukodystrophy. As for assays for more common diseases, it is important to achieve congruence when multiple clinical laboratories provide testing. Four clinical laboratories, one research laboratory, and a commercial vendor collaborated with the goal to achieve congruence in quantitative psychosine measurement in DBS. A set of DBS calibrators was prepared by a single vendor and used in each reference laboratory to make a standard curve of measured psychosine in DBS versus the stated calibrator psychosine level. Congruence between the participating five laboratories was achieved using the psychosine DBS calibrators. This allowed application of disease-specific reference ranges obtained by the reference laboratory with the most extensive data by the other reference laboratories. Congruence between multiple reference laboratories in the measurement of the absolute concentration of biomarkers in DBS (and by extension other samples) is possible by the use of a common set of DBS calibrators.