Measurement of serum folate by 75Se-selenofolate radioassay. Results of a multi-institutional clinical trial

Folate assays--an alternative to microbiological assays and commercial kits

A simple and reliable folate radioassay technique based on the principles of classic folate radioassays but incorporating several of the recently introduced technical innovations is presented as an alternative to the microbiological assays and commercial kits. Serum and red cell folate values from this method were compared with results from two commercial kits and a Lactobacillus casei (L. casei) assay. There was a good correlation with the L. casei assay for both serum and red cell folate (r = 0.95). The method uses N-methyltetrahydrofolate standards diluted in folate free serum, beta-lactoglobulin as a binder and an alkaline denaturation ('no-boil') of endogenous folate binding proteins. Low hematocrit lysates were best performed at a 1 in 10 rather than 1 in 20 dilution. A comparison of the boil and 'no-boil' kits from Diagnostic Products Corporation revealed that the 'no-boil' kit produced results closer to those obtained from the L. casei assay than the boil kit.

An evaluation of commercial radioisotope methods for the determination of folate and vitamin B12

Five commercial kits for the determination of folate and six kits for the determination of vitamin B12 were investigated. Their performance has been compared with microbiological methods for the two vitamins and with a non-commercial radioisotopic method for B12. The results show the importance of the determination of the reference range for an individual laboratory for each method. The precision of the kits varied appreciably, as did their performance using specimens from patients with different haematological disorders. In particular, certain kits failed to detect all patients with pernicious anaemia. The relative accuracy of the kits was assessed. Various factors which should be taken into account in the final selection of a satisfactory kit are discussed.