Blood was collected in 10 mL Vacuette serum clot-activator tubes (Greiner Bio-one, product number 455092) before 12 AM. Blood was allowed to clot for 30 min at room temperature and serum was stored in aliquots at −80°C in the Auria Biobank (Turku, Finland) within 2 hours of sampling. Frozen samples were shipped on dry ice to Basel, Switzerland, where sNfL concentrations were measured by a single molecule array assay (Simoa Technology).14 15 (link)