Serum folate optimal range and reference range

Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026

Sera's bands for Serum folate:

Optimal 10 – 20 ng/mL (23 – 45 nmol/L); sufficient 3 – 30 ng/mL (7 – 68 nmol/L); out of range below 3 ng/mL.

Evidence grade: Established clinical threshold. A band edge that corresponds to a recognised diagnostic, risk or treatment threshold from a major clinical guideline or public-health body.

All units

Unit	Optimal	Sufficient	Out of range
ng/mL	10 – 20	3 – 30	below 3
nmol/L	23 – 45	7 – 68	below 7
μg/L	10 – 20	3 – 30	below 3

Bounded on the low side only — a high result is not treated as out of range. The published thresholds define deficiency only; a high serum folate usually reflects supplements or fortified food.

What the evidence says

The acceptable band starts at 3 ng/mL (about 7 nmol/L), the level below which WHO and NIH define folate deficiency; Mayo Clinic Laboratories uses 4. Laboratories publish no upper limit, so a high result is not flagged. The optimal band of 10 to 20 ng/mL has no published threshold behind it. Serum folate reflects recent intake, so one low result does not establish long-term status.

Sources

Folate - Health Professional Fact Sheet — NIH Office of Dietary Supplements, 2022 · Government / public-health guidanceA serum folate above 3 ng/mL indicates adequacy; the measure is sensitive to recent intake. Matches Sera's sufficient lower edge exactly. Updated November 30, 2022.
Folate (Folic Acid) — Labcorp, 2026 · Laboratory / reference-interval sourceReference range above 3.0 ng/mL, with no upper limit; below 3 ng/mL is clinical deficiency per the World Health Organization. Matches Sera's sufficient lower edge exactly.
FOL - Folate, Serum: Clinical & Interpretive — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceReference value 4.0 mcg/L or more, with no upper limit; below 4.0 suggests deficiency, a consensus cut-off derived from NHANES III. Close to Sera's sufficient lower edge of 3.

What Folate (Serum) measures

A B vitamin needed for cells to divide and for a process called methylation, measured in serum.

Serum folate tracks the last few days of intake, where red cell folate tracks the last few months — a normal serum folate on the morning after a leafy meal says little about status. Read it with B12: repleting folate alone can mask a B12 deficiency while the neurological damage continues.

Related vitamins & minerals markers

See Serum folate in the full list of biomarker ranges

This page is a reference for practitioners, not medical advice. Sera's bands are practitioner targets for structured review, not diagnostic thresholds, and Sera does not diagnose or recommend treatment. Read a result alongside the interval printed by the issuing laboratory and the client's history and symptoms. Range set: Sera Production, version 1.0, last reviewed November 9, 2026.