Human biomarkers of population folate intake
Population monitoring of folate status can provide an indication of the efficacy of supplementation or fortification initiatives, alongside epidemiological prevalence data of the effects of folate deficiency such as NTDs. Folate status is most often measured in women of reproductive age and general adult populations, and data on preschool children and pregnant women are generally lacking (3). Future research efforts should also consider these life-stage groups for population surveillance.
There are several methods currently available to measure folate status, as outlined in the table below. The microbiological method is considered the gold standard of folate assessment and is suitable for use in all laboratories. It can be used with serum or whole blood.
Serum folate is a marker of acute folate status and red blood cell (RBC) folate one of chronic status, but several repeated low measurements of serum folate can also indicate deficiency.
The UK and USA use LC-MS/MS for population monitoring specifically to be able to distinguish between folic acid and other endogenous folates due to monitoring fortification and any adverse side effects.
Table: comparison of current methods in use for folate assessment (13)
Methods
Folate Forms
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).
- Folate with B12: Using a kit with serum or whole blood.
Total folate
Microbiologic assay for use with serum or whole blood.
- Microbiologic assay training: Through a collaboration between the Folate Task Team of Nutrition International and the CDC Foundation, CDC is supporting training and facilitating capacity development to conduct folate microbiologic measurements in multiple international laboratories.The folate microbiologic assay will allow countries to assess population folate status. This will have a long-term global health impact by providing countries with the knowledge to identify folate insufficiency, determine appropriate interventions and reduce the risk of neural tube defects.
- Click on the links above for more details, write to the Folate Task Team at Nutrition International: folatetaskteam@nutritionintl.org
- Quality control A recent paper by the US CDC gives a framework for laboratory harmonisation of folate measurement in LMICs (12), and they are currently setting up a scheme to help LMIC laboratories set up the microbiological method in collaboration with Nutrition International. More information will be posted on this page as this scheme becomes available.