B. Kelleher

AIMS: To develop a simple microbiological assay for serum and red cell folates on 96-well microtitre plates, suitable for use in routine clinical diagnosis. METHODS: Use of a chloramphenicol resistant organism (NCIB 10463) saved time by avoiding aseptic precautions. Use of plate sealers facilitated mixing. Evaluation of assay performance included estimations of folate recovery, assay reproducibility, and response to reduced folate. Results obtained on sera (193) and red cell folates (150) were compared with those obtained using a traditional microbiological assay. RESULTS: Good recovery of folic acid added to serum and also good interassay and intra-assay precision were obtained with both serum (CV% of less than 5) and red cell folate pools (CV% of less than 5). Equimolar assay responses were obtained with folic acid, 5-formyltetrahydrofolate (L-form), and 5-methyltetrahydrofolate (L-form). The microassay correlated well with a traditional assay for estimation of folate in both serum (n = 193, r = 0.975) and red cells (n = 150, r = 0.96). CONCLUSIONS: This assay is more compact and less time consuming than the traditional assay. It is extremely economical and is easy to perform in a routine clinical laboratory.

Dried blood spots (DBS) on filter paper have potential as a collection method in screening for haematinic deficiencies. Factors influencing the volumetric precision of uniform 'centre' punches (6.35 mm diameter) removed from dried blood spots have been evaluated. The volume of blood in each DBS punch (n = 234) was greatly influenced by both sample haematocrit (r = 0.63) and haemoglobin concentration (r = 0.63). The volume in identical punches (n = 57) also differed significantly when measured independently using either 125I human serum albumin or haemoglobin relative to the original blood sample. DBS punch volumes should be predetermined for individual batches of filter paper using the specific analyte of interest.

The results of a large number of nutritional screen requests (n = 871) were compared with corresponding values of erythrocyte indices considered predictive of nutritional deficiencies to determine if such indices could be used in a prospective screening procedure to restrict the number of serum vitamin B12, folate, and ferritin assays. Low mean cell haemoglobins (MCH less than 27 pg) were found to be superior to low mean cell volumes (MCV less than 77 fl), in predicting low serum ferritin values. The occurrence of deficient ferritin values was 90% when the MCH was very low (MCH less than 23 pg). Vitamin B12 or folate deficiency could not be predicted from the MCV. A normal MCV was found in more than 55% of vitamin B12 deficient samples and some 30% of serum B12 deficients (less than 150 micrograms/l) showed no evidence of anaemia (Hb greater than 12 gm/dl) or macrocytosis (MCV less than 100 fl). It would not seem appropriate to use erythrocyte indices alone as a method of selecting samples for further investigation of folate or vitamin B12 status.

Folic acid deficiency is common in the elderly population, resulting in anaemia, dementia, many neurological sequelae and an indirect role in atheromatous disease. An increase in natural food folate is relatively ineffective at increasing folate status and the use of folate fortification of foodstuffs is recommended. The aim of our study was to assess the benefits of folic acid-fortified milk to the folate status of an elderly institutionalised population. 49 subjects received fortified milk as part of their daily diet for at least 6 months (active group) and 40 subjects received unfortified milk (control group). Our results showed a mean serum folate level in the active group of 5.81 (1.1-17.6) microgram/l compared to the control group mean of 2.16 (0.5-9.4) microgram/l (p < 0.001; normal range for serum folate 2.7-20 microgram/l). Similarly the mean red cell folate level in the active group of 316.5 (130-905) microgram/l was significantly higher than the control group mean of 196.1 (95-490) microgram/l (p < 0.001; normal range for red cell folate 150-1,000 microgram/l). Our results suggest that folic acid-fortified milk is an efficacious and acceptable method of administration of folic acid in the elderly population and we recommend the use of folic acid-fortified milk in the regular daily diet of the elderly population.