Why are we still measuring red cell folate instead of just serum folate?

As with most other vitamins, the assessment of biological stores and intake is based on the concentration in body fluids. Studies of folate status have traditionally used serum/plasma or red blood cell folate. Both assays are widely available in laboratories. Red cell folate, favoured by many clinicians, is the more labour intensive test and therefore more costly than serum folate. Turnaround time is also longer because of the need to determine the haematocrit using a haematology cell counter followed by preparation of a haemolysate from the whole blood prior to running the assay. Factors related to the pre-treatment procedure, haematocrit and oxygenation of haemoglobin all contribute to analytical variability of red cell folate, [1] making coefficients of variation for red cell folate assays close to twice those of serum folate assays. The cost of red cell folate is between 40% and 55% higher than that of serum folate in the private sector and the South African National Health Laboratory Service (NHLS) respectively. We recently carried out a retrospective analysis of red cell and serum folate requests in the Tshwane metropolitan(Pretoria) area. Of the almost 21 000 tests requested over an eight-year period, 2% demonstrated folate deficiency. This relatively low prevalence most likely reflects the success of the mandatory food fortification programme implemented in South Africa in October 2003 and is consistent with figures reported by studies conducted after introduction of fortification in other countries. [2]