Hiu
@hill4332, I can see a new greeting for those one meets," Hello there, how is your folate level"?
I hope the following might clear up some of the confusion, based on what I could source and not as professional advice or opinion: There are two folate tests - serum folate and RBC folate. Serum folate is said to be less accurate than the RBC(red blood cell) folate readings as far as establishing if the body is short of folate. Serum is the fluid in blood less the cells in the blood. The red blood cell seems to reflect what is happening in the rest of the cells of the body.
The serum folate might be tested for first and if lowish the RBC folate is then measured to get a better idea of the more true picture. (see nps.org.au Appropriate use of tests for folate and B12 deficiency - Metz J, Australian prescriber Feb 1999)
In 2005
WHO (not the mob working out of a blue telephone box)! put the
lower limits for all age groups as:
serum folate < 4 ng/ml (< 10 mmol/l) and RBC folate as <151 ng/ml (< 340 mmol/l). The only exception is in pregnancy apparently as folate levels fall over the duration of the person's pregnancy.( apps.who.int Serum and RBC folate concentrations for assessing folate status in populations WHO 2012).
In the first reference the author stresses the
importance of discovering why the folate level in the body is low. The causes to consider at the top of the list are
dietary deficiency - leafy green vegetables being an oft quoted source and
malabsorption and in particular coeliac disease. Has your doctor checked for coeliac disease?
Because there is a connection in the way folate and B12 are used by the body, if folic acid supplements are taken this can lower the serum B12 level. So folate and B12 are usually measured together (livestrong.com "What is the relationship between folate and vitamin B12? Oct 2017.
I hope the above is helpful and clearer than mud !!
). And I am certainly feeling better, although I was feeling rough enough that I implemented a few changes at the same time, so wouldn't like to claim any miraculous benefits from my 1 folate tab a day. 
