Quality control and references
For quality control measures for each of the methods, see the links given on page 3.
Serum folate: Serum folate is stable in the refrigerator for up to 1 week or for several years if stored frozen at -70°C. Serum folates are stable through 3 freeze thaw cycles with minimal exposure to ambient temperature but deteriorate with further freeze thaw cycles. Serum folates show up to a 10% loss when exposed to ambient temperature for 5 hours (15).
Red cell folate: The short term stability of whole blood total folate in unfrozen haemolysates is worse than that for whole blood but haemolysates are stable for up to 4 days if refrigerated and for several years if stored frozen at -70°C. Whole blood folate without tetrahydrofolate shows good stability with up to 3 freeze thaw cycles but a 20% loss after 2 freeze thaw cycles with samples containing tetrahydrofolate (15).
The US CDC VITAL-EQA program helps labs maintain and improve the quality of their measurements for biochemical indicators, including serum folate.
If you are interested in participating in the program, or would simply like further information, write to firstname.lastname@example.org
A recent paper by the US CDC gives a framework for laboratory harmonisation of folate measurement in LMICs. The CDC are currently setting up a scheme to help LMIC laboratories set up the microbiological method in collaboration with the Micronutrient Forum. More information will be posted here as this scheme becomes available.
For questions on methods of folate assessment or for technical assistance, please OpeN-Global, or write to:
NIHR BRC Nutritional Biomarker Laboratory, University of Cambridge, UK