Vitamin B 12: Patients taking vitamin B12 supplementation may have misleading results.
Many other conditions are known to cause an increase or decrease in the serum vitamin B 12 concentration including: Increases: Ingestion of vitamin C, ingestion of estrogens, ingestion of vitamin A, hepatocellular injury, myeloproliferative disorder, uremia. Decreases: Pregnancy, aspirin, anticonvulsants, colchicine, ethanol ingestion, contraceptive hormones, smoking, hemodialysis, multiple myeloma.
The evaluation of macrocytic anemia requires measurement of both vitamin B 12 and folate levels; ideally they should be measured simultaneously.
Folate: Patients with combined deficiency of folate and iron may not demonstrate the erythrocyte macrocytosis otherwise typical of folate deficiency anemia. In these patients, however, the red cell distribution width (RDW) will typically be elevated.
A non-fasting specimen results in falsely elevated results.
Patients taking folate may have misleading results.
Folates other than (N)-5-methyltetrahydrofolate and folic acid antagonists (such as methotrexate) may, under some circumstances, be present in serum and will also be measured by this method.
The analytic variability (CV) of both serum and red blood cell folate assays is considerable. Homocysteine and methylmalonic acid levels are alternate determinates of folate deficiency.