Radioassay for serum and red cell folate
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 $sup 125$I-tyramide of PGA. Like the $sup 3$H-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 predominant 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 casei 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 $sup 125$I-PGA as compared to $sup 3$H-PGA, the fact that various powdered milks differ widely in folate-binding capacity, and that only about 60 percent of commercially obtained skim or powdered milk preparations appear to contain the substance which splits folate from serum binder. (auth)
- Research Organization:
- Bronx Veterans Administration Hospital, NY
- NSA Number:
- NSA-33-017567
- OSTI ID:
- 4119118
- Journal Information:
- J. Lab. Clin. Med., v. 87, no. 1, pp. 138-151, Other Information: Orig. Receipt Date: 30-JUN-76
- Country of Publication:
- United States
- Language:
- English
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