Lefeber DJ 1 1 Radboud Nijmegen Medical Centre, Nijmegen, Netherlands In the framework of the European program Euroglycanet, a quality control scheme was set up for the screening of Congenital Disorders of Glycosylation by analysis of transferrin glycosylation. Reproducibility problems after 3 rounds among Euroglycanet members necessitated an elaborate stability experiment. Serum samples were stored at different temperatures and lyophilisation conditions, after which the stability was tested using transferrin isofocusing during a 1-year follow up. Samples lyophilized in the presence of cryoprotectant were stable at shipment conditions for at least 2 months. Since 2009, the scheme is supervised by ERNDIM and open to other laboratories world-wide. Currently, 51 centres participate. In view of the very limited amount of patient material, the scheme operates with 20 microliter serum per sample. Different techniques are used for analysis of transferrin glycosylation, including isofocusing, capillary electrophoresis, HPLC and mass spectrometry. The samples originate from patients with a known CDG subtype or a secondary cause of abnormal transferrin glycosylation. The results are interpreted against a clinical information, provided with the samples. Scoring is based on profile interpretation and suggestions for follow-up diagnostics, and showed clear improved over the years. The results of this novel CDG QC scheme in ERNDIM's regular QC program will be presented.