The various analytes have different stability in serum. Serum TLI and PLI are stable for up to 2 weeks at room temperature. However, serum folate shows limited stability at room temperature. Therefore, serum samples for folate analysis should be kept at 4ºC for not longer than 48 hours, but freezing is preferred. Furthermore, folate is light sensitive and samples should be stored in the dark or wrapped in foil. We recommend that samples for serum cobalamin/folate analysis are shipped overnight either frozen or at least with included ice packs to keep them cooled during shipment.