Assessing the influence of 5,10-methylenetetrahydrofolate reductase polymorphism on folate stability during long-term frozen storage, thawing, and repeated freeze/thawing of whole blood

BackgroundLimited information is available on folate stability, particularly vitamer stability by 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T genotype, during frozen storage, thawing, and repeated freeze/thawing (F/T) of whole blood (WB).MethodsWe assessed folate stability after storing undiluted WB for up to 30 mo at − 70 °C and measuring folate vitamers by LC–MS/MS at 6, 14, 20 and 30 mo in samples with C/C and T/T genotype (n = 13 each). We investigated folate stability during 3-h thawing of WB (n = 2 each/genotype) and during repeated F/T of WB (n = 4 each/genotype).ResultsWe found significant decreases in total folate (TFOL) (median decrease: 8.8% for C/C and 16% for T/T), methyl folate (7.9% for C/C and 10% for T/T), and non-methyl folate (19% for C/C and 24% for T/T) concentrations from 6 to 30 mo WB frozen storage. During thawing of WB at room temperature and repeated F/T, samples with T/T genotype were susceptible to greater folate losses than samples with C/C genotype.ConclusionsLong-term frozen storage of WB resulted in significant folate losses of ~ 10–25% that are clinically unacceptable. Frozen WB should not be exposed to more than 1 h of thawing time and repeated F/T of WB should be avoided.

► Storing undiluted whole blood at − 70 °C for 2 y results in folate losses of ~ 10–25%.
► Thawing of frozen WB must be carried out within < 1 h to avoid folate losses.
► Repeated freeze/thawing of whole blood should be avoided when possible.