Comparison of commercial kits for radioimmunoassay: III. Radioassay of serum folate.

We evaluated six commercial radioassay kits in which tritium or iodine tracers are used to measure serum folate. We assessed the adequacy of the literature supplied with the kits, within-run precision, reagent stability, analytical recovery of added pteroylglutamic acid and N-methyltetrahydrofolic acid, results of analysis of patients' samples, and minimum detection limits. There were serious discrepancies among manufacturers' kits in each of these respects. Such discrepancies could affect interpretation of results and of data on like samples derived from different laboratories that are using different kits. Laboratories are urged to assess carefully the materials and method supplied by a manufacturer before putting a kit to clinical use.