Jan 1, 1976

Radioassay for serum and red cell folate

The Journal of Laboratory and Clinical Medicine
D L Longo, V Herbert

Abstract

A simple, reliable assay for serum and red cell folate is described. It uses plain untreated liquid or powdered milk, requiring no special handling or purification, as binder. Such milk makes it possible to ignore endogenous serum folate binder, since crude (but not purified) milk contains a factor which releases folate from serum binder. It simplifies counting radioactivity by employing a gamma emitting isotope of pteroylglutamic acid (PGA), namely the 125I-tyramide of PGA. Like the 3H-PGA assay of Givas and Gutcho, it permits the use of stable PGA rather than unstable methyltetrahydrofolic acid (MeTHFA) standards, because it is carried out at pH 9.3, a pH at which milk folate binder is unable to distinguish PGA from MeTHFA, which is the predominat folate in human tissues. The equipment required to do the radioassay is present in most diagnostic chemistry laboratories. Results are essentially identical to the generally accepted Lactobacillus casel microbiologic method of folate assay, except that false low results are not produced in the radioassay by antibiotics, tranquilizers, and chemotherapeutic agents. Three caveats in its use are the relative instability of 125I-PGA as compared to 3H-PGA, the fact that various powdered m...Continue Reading

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Mentioned in this Paper

Antineoplastic Agents
Calcium
Antibiotic throat preparations
Antifungal Antibiotics, Topical
Serum Proteins
Folate Serum
Tetrahydrofolates
Antibiotics, Gynecological
Tritium
Folate

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