What does the Serum Folate test measure?

Why is Serum Folate measured?

Folate deficiency causes megaloblastic macrocytic anaemia morphologically identical to B12 deficiency — both impair thymidylate synthesis and produce the characteristic hypersegmented neutrophils and macro-ovalocytes on blood film. The critical clinical distinction is that folate supplementation can correct the haematological manifestations of B12 deficiency while leaving the neurological manifestations (subacute combined degeneration) to progress undetected — making simultaneous B12 and folate assessment mandatory before folate supplementation is initiated in any patient with macrocytic anaemia. Folate deficiency is particularly relevant in pregnancy (neural tube defect risk), alcohol use disorder (impaired absorption and intake), methotrexate therapy (DHFR inhibition), and patients on anticonvulsants. In the anaemia panel, folate assessment closes the macrocytic anaemia workup alongside B12.

Reference ranges

Standard reference

>3.0 ng/mL (>6.8 nmol/L) # REVIEWER FLAG: Confirm Access Medical Laboratories reference range for serum folate — the lower limit varies between laboratories (some use >2.7, others >4.0 ng/mL). Confirm whether Access Medical Laboratories reports serum folate, RBC folate, or both. RBC folate (150–450 ng/mL RBC) reflects tissue folate stores over the erythrocyte lifespan and is a more stable, nutritionally meaningful marker than serum folate, which reflects recent dietary intake and fluctuates substantially with meals. Confirm which specimen type is included in the Access Medical Laboratories Anaemia Panel.

Functional medicine optimal

>10 ng/mL serum folate (functional medicine optimal for adequate methylation capacity and erythropoietic support, particularly relevant in pregnancy, MTHFR polymorphism carriers, and patients with elevated homocysteine); RBC folate >250 ng/mL RBC. # REVIEWER FLAG: Functional optimal for serum folate varies between integrative practitioners — reviewer to confirm and whether MTHFR status should be referenced in the optimal range context.

Units

ng/mL, nmol/L

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.