FOLATE ASSAYS - SERUM OR RED-CELL

Tests for folate and vitamin B-12 deficiency are frequently requested by clinicians in many different specialties. An audit of folate assay methodology was undertaken to establish the number of tests and types of assay performed in different centres, and to analyse the indication s for these investigations, with a view to advising on the most approp riate assay for use in the laboratory. A questionnaire was sent to 30 centres, 24 (80%) of which participated in the audit. The types of fol ate assay performed, number of requests, reference range and method of analysis differed between centres. The major specialty users of the s et-vice were general practitioners, general physicians and geriatricia ns. A detailed analysis of 1,259 consecutive requests for folate assay s from a single representative laboratory showed a significant correla tion between serum and red cell folate levels (r = 0.49, p < 0.001). H owever, in patients with low serum folate, there was no correlation wi th red cell folate in the absence of macrocytosis. The major indicatio n for folate analysis was for haematological abnormalities but 36% of cases were for nonspecific indications. A haematologist with an intere st in folate metabolism was invited to moderate the results at an audi t meeting of haematologists. The consensus was that the most appropria te screening test for folate deficiency is the serum assay, which can be combined easily with vitamin B-12 assay.