Clinical utility of serum folate measurement in tertiary care patients: Argument for revising reference range for serum folate from 3.0ng/mL to 13.0ng/mL

Objective: Assess the need for folate testing, frequency of corrective action, and determine reference level for serum folate. Methods: Serum folate levels in 5313 samples from 4448 patients, and clinical data were reviewed for patient characteristics and for (a) evidence of corrective action in patients with serum folate values <5.5 ng/mL, and (b) differences in patients with serum folate levels <5.5 ng/mL and patients with levels >25.7 ng/mL. Results: The prevalence of serum folate levels, in patients, <3.0, <4.0, <5.5, <7.0 and <13.0 ng/mL was 0.58%, 1.55%, 4.9%, 9.98% and 43.21% respectively. Patients with serum folate levels <5.5 ng/mL had lower serum albumin and hemoglobin. In 64% of patients with serum folate >25.7 ng/mL the sample was collected after supplementation with folic acid. Of the 128 patients with serum folate <5.5 ng/mL documentation of supplementation was present in only 38.9%. Conclusions: Serum folate levels are below the current "normal" level of 3.0 ng/mL in a larger proportion of tertiary care patients than that reported for ambulatory patients. In patients with folate deficiency, corrective action is lacking in >60% of the patients. Since serum folate levels ≥13.0 ng/mL are needed for optimal prevention of neural tube defects in the embryo/fetus, we propose that normal serum folate level should be designated to be ≥ 13.0 ng/mL.