Measurement of serum folate: experience with 75Se-selenofolate radioassay.

Abstract

SUMMARY Three hundred and eighty-two serum samples were assayed for folate content by a standard Lactobacillus casei microbiological assay and by radioassay using the 75Se-selenofolate radioassay kit from the Radiochemical Centre, Amersham. Results showed encouraging concordance. Explanations were discovered for the few disparities. The radioassay procedure is simple and an assay batch can be completed in one working day.We wish to document our results from measurements of serum folate levels by both microbiological assay and radioassay. SamplesThree hundred and eighty-two successive samples of clotted blood, submitted over a 25-week period to the haematology laboratory at St George's Hospital for serum folate assay, were separated and stabilised for purposes of radioassay by the addition of about 5 mg of sodium ascorbate per millilitre of serum. Ascorbic acid was added to the samples for microbiological assay. The folate content of these samples was measured both by a radioassay method and by microbiological assay. Each assay was conducted in ignorance of the result obtained by the other method by another operator.Forty-five blood samples in sequestrene were assayed for their red cell folate content. Samples for microbiological assay were prepared as a 1:10 dilution of whole blood in 1 % aqueous ascorbic acid, with a drop ofTween 80 solution. Those samples for radioassay were prepared as a 1:8 dilution in glass-distilled water and, after complete haemolysis, sodium ascorbate was added to a final concentration of 5 mg/mi. Methods MICROBIOLOGICAL FOLATE ASSAYThe Lactobacillus casei method of Waters and Mollin (1961) was used for serum folate assay. Red

Determination of Blood Folate Using Acid Extraction and Internally Standardized Gas Chromatography–Mass Spectrometry Detection

“…The myriad forms of folates have hindered development of analytic techniques that detect specific congeners and the majority of measurements are reported as total folate. Popular methods for folate measurement include microbiological growth assays that use folate-responsive microorganisms (8 -11) or radiolabeled folate binder assays that operate on the principle of competitive binding between endogenous and exogenous (radiolabeled folate) folates for a limited amount of a protein binder (12)(13)(14)(15)(16)(17)(18). Folate assays that involve the use of HPLC (19 -22) and GCMS (23) methods for blood and tissues are less commonly used, but have the potential for providing superior specificity and analytic precision.…”

Measurement of red cell folate with 75Se-selenofolate radioassay.

“…Details of the method recommended for serum folate assay were described by Johnson et al (1977). Received …”

“…These were placed in a water bath at 100°C for five minutes and then cooled to ambient temperature. The method then followed the protocol described (Johnson et al, 1977).…”

“…A preliminary attempt to use selenofolate radioassay to measure red cell folate yielded a correlation coefficient (r) of 0-6 with Lactobacillus casei microbiological assay (Johnson et al, 1977). We describe some simple adaptations of the radioassay and our initial experience with the adapted method.…”

Estimation of serum folate by a radioassay and a continuous-flow method, compared with an established microbiological tume assay.

“…The radioassay kit (The Radiochemical Centre, Amersham, Bucks, UK) utilised 75Se labelled folate (Johnson et al, 1977). Supernatants were counted on a Wallac 300 gamma counter (LKB, South Croydon, Surrey, UK) and the results were calculated as recommended (Radiochemical Centre, 1976).…”