Folic acid binding protein and folate balance in uremia

To determine the incidence and importance of folate deficiency in uremia, we studied 41 patients who had chronic uremia but who were not receiving hemodialysis. Serum folate level was assayed by microbiological, whole serum radioassay, and heat-extracted radioassay techniques. Mean serum folate level, as determined with the Lactobacillus casei method, was 6.9 ng/ml (normal, more than 3.0 ng/ml). The mean heat-extracted radioassay serum folate level was 6.6 ng/ml. Only 10% of our patients had subnormal serum folate values, as determined with these techniques. No cases of megaloblastic anemia were discovered, and the hematologic profiles correlated with L casei and heat-extracted radioassay serum folate values. The mean serum folic acid binding protein (FABP) level was significantly greater for the uremic patients than for control patients (26% vs 9.9%, respectively; P = .0005). Our results show that elevated levels of serum FABP spuriously depress the serum folate level, as determined with the whole serum radioassay technique, but apparently do not retard delivery of folate to the tissue in vivo.