[Folate determination in serum for clinical use (author's transl)]

Folate deficiency may be diagnosed in man by measuring serum folate activity using either a microbiological procedure with L. casei or a radioassay. The microbiological procedure tends to be time consuming and tedious, as compared with the radioassay; nevertheless it allows the accurate determination of each folate derivative that is normally present in serum. The comparison of serum folate levels obtained by the two methods shows an adequate correlation. However, it results from individual samples show that the values obtained by the radioassay are lower than the microbiological ones by 10-30%. The lower results in the radioisotope test may be caused by the presence of high levels of unsaturated endogenous protein binders in serum and/or by the difference in affinity of lactoglobulin - the binding protein used in the test - for folic acid (standard) and 5-methyl FH4 or 10-formil FH4 (serum).