Quality control and references

Quality Control

For quality control measures for each of the methods, see the links given on page 3.

Sample stability

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).

Laboratory accreditation

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 vitaminalab@cdc.gov

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.

Folate-specific information:

• UK NEQAS have a heamatinics scheme which includes total folate in serum and red cells.
• ARUP Laboratories: A National Reference Laboratory is a non-profit laboratory at the University of Utah which is a global leader in clinical and pathological test development. It provides accreditation for folate (and vitamin B12).  For further information, consult this page.
• For more details on other laboratory accreditation, validation or proficiency testing schemes, please see the OpeN-Global page on Laboratory accreditation.

Technical assistance

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
Email: nbl@mrc-epid.cam.ac.uk