Evaluation of a commercial radioisotopic kit for folate assays.

Abstract

SUMMARY A commercial kit for the radioisotopic assay of folate in serum, the Bio-Rad 'Quanta Count' folate kit, produced lower results than the Lactobacillus casei microbiological assay method.Its normal range was 2-0-13 0,ug/l and the reproducibility was similar to that of the microbiological assay method. The kit was also satisfactory for whole blood folate assays. The cost requires careful consideration before the kit is used for routine purposes.For many years most laboratories have depended upon a microbiological technique for folate assays. Radioisotope methods using tritium or carbon-14 labels have been available, but their use has been limited by the expense of appropriate counting equipment. Recently, however, several commercial kits using radioiodinated labelled folate compounds, measurable in widely used gamma counters, have appeared, and we here report our experiences with one of them including comparison with a microbiological assay. Material and methods RADIOISOTOPE TECHNIQUE'Quanta Count' folate kits were supplied by Bio-Rad Laboratories Ltd. The radio-ligand method is based on the principle of saturation analysis. Each kit contains iodine-125 (1251) labelled pteroyl glutamic acid (Pte-Glu) derivative, borate buffer pH 9-6, absorbent charcoal tablets, and ,8 lactoglobulin as binding agent. The six standards supplied consist of lyophilised folate-free human serum containing varying amounts of Pte-Glu, range 0-20 ug/l when reconstituted. The kits available are sufficient for testing 44 or 94 unknown samples in duplicate; 0-1 ml of sample is diluted in 1-0 ml of isotope in borate buffer. The diluted samples are heated for 15 minutes in a boiling bath and cooled to room temperature; 1I0 ml of binder is added and the samples are incubated at room temperature for 30 minutes. An absorbent tablet is added to each tube and, after vortex mixing, the tubes are centrifuged.

The diagnosis of megaloblastic anaemia

“…It is not affected by prior administration of antibiotics or of antifolate drugs and the red cell folate need not previously be deconjugated. Numerous assay kits are now available and their performance compared with microbiological assay has been evaluated in several recent publications (Kubasik, Votosin & Sine 1975, Waddel et al 1976, Hill & Dawson 1977, McGown et al 1978. Although radioassay measures all the circulating folate rather than specific analogues, it tends to yield lower results-ranging from 50% (Rothenberg da Costa & Rosenberg 1972) to 90% (Waddel et al 1976) of those obtained by radioassay and iodinated kits have been found to give consistently lower values than tritiated kits (Kubasik et al 1975).…”