Folate and vitamin B12 levels in an urban elderly population with chronic diseases. Assessment of two laboratory folate assays: microbiologic and radioassay.

Folate levels of serum and red blood cells (RBC) and vitamin B12 serum levels were investigated in 326 urban chronically ill elderly ambulatory patients and 41 healthy young control subjects. Two laboratory methods were used for investigating the folate levels, the microbiologic assay (MBA) with Lactobacillus casei and radioassay (RA). Serum and RBC samples of 326 patients were tested by the folate MBA and 270 of the same samples by the RIA methods. In the MBA 6.8% of the patients and 12.2% of controls had low levels of folate RBC (less than 200 ng/mL) and 1.8% of patients and 4.8% of controls had low serum folate levels (less than 5 ng/mL). All of the patients with the low folate levels had normal hematologic findings and no clinical symptoms of folate deficiency. In the RIA method, all of the patients and almost all of the control subjects (except one) had normal folate levels. Ten of the patients (3%) had low levels of serum vitamin B12 (less than 200 pg/mL). They were hematologically normal. They had normal Schilling tests and normal vitamin B12 dietary intake. Their RBC folate levels were normal and even somewhat higher. Forty percent of these patients had macular degeneration of the eyes. The data indicate the superiority of the RA method over the MBA and bring into question the accuracy of previous studies. The data furnish further evidence that a low vitamin B12 level in the elderly is not necessarily a true vitamin B12 deficiency and raise the possibility of an association between low B12 serum levels and macular degeneration of the eyes.