Is a serum folate concentration of 18.5 ng/mL normal, and does the patient require folic‑acid supplementation?

Serum Folate 18.5 ng/mL: Normal Status, No Supplementation Required

A serum folate concentration of 18.5 ng/mL is well above the deficiency threshold and falls within the optimal range; routine folic acid supplementation is not indicated unless you are a woman of reproductive age or have specific risk factors. 1

Understanding Your Folate Level

Your serum folate of 18.5 ng/mL converts to approximately 40.8 nmol/L, which is substantially above all deficiency cutoffs:

• Deficiency threshold: <10 nmol/L (4.4 ng/mL) 1
• Marginal deficiency: 7-14 nmol/L (3.1-6.2 ng/mL) 2
• Optimal level for neural tube defect prevention: ≥13.0 ng/mL 3, 4
• Level associated with homocysteine elevation: <8 μg/L (18 nmol/L or approximately 8 ng/mL) 2

Your level of 18.5 ng/mL exceeds even the proposed optimal threshold of 13.0 ng/mL, indicating adequate recent dietary folate intake and sufficient circulating folate. 3, 4

Who Needs Supplementation Despite Normal Levels

Even with your normal folate status, supplementation is recommended if you fall into these categories:

Women of Reproductive Age

• All women aged 12-45 years with preserved fertility should take 400 mcg (0.4 mg) folic acid daily, regardless of pregnancy plans, to prevent neural tube defects 3
• Women with BMI >30 kg/m² or type 2 diabetes require 5 mg daily during periconception and first trimester 1
• Women with prior neural tube defect-affected pregnancy require 4 mg daily starting 3 months before conception through 12 weeks gestation 3

High-Risk Medical Conditions

• Patients on methotrexate: 5 mg weekly (24-72 hours post-dose) or 1 mg daily for 5 days weekly 3
• Patients on sulphasalazine: 1-5 mg daily, or folinic acid 15 mg daily for more efficient repletion 3
• Chronic hemodialysis with hyperhomocysteinemia: 5 mg daily (non-diabetic) or 15 mg daily (diabetic) 3
• Inflammatory bowel disease: Regular supplementation, especially if on antifolate medications 3
• Alcohol use disorder: 1-5 mg daily with monitoring every 3 months 3

When to Recheck Folate Levels

You do not need routine follow-up testing unless:

• You develop macrocytic anemia (MCV >100 fL) 1
• You start medications that interfere with folate metabolism (methotrexate, sulphasalazine, anticonvulsants) 3
• You develop chronic alcoholism or malabsorption syndromes 3
• You are diagnosed with inflammatory bowel disease 3

Critical Caveat: Vitamin B12 Status

Your normal folate level does not exclude vitamin B12 deficiency. High folate can mask B12 deficiency by correcting megaloblastic anemia while allowing irreversible neurological damage to progress. 1, 3 If you have any of the following, check vitamin B12 and methylmalonic acid (MMA):

• Neurological symptoms (paresthesias, ataxia, cognitive impairment) 1
• Macrocytic anemia despite normal folate 1
• Age >60 years, vegetarian/vegan diet, or history of gastric surgery 1
• Chronic proton pump inhibitor or metformin use 1

Bottom Line

Your serum folate of 18.5 ng/mL indicates adequate folate status. No supplementation is needed unless you are a woman of reproductive age (in which case take 400 mcg daily regardless of folate level) or have one of the specific high-risk conditions listed above. 1, 3, 4