Not medically reviewed
Haematology
Folate (vitamin B9)
Not medically reviewed · Content last updated · 1 min read ·
This is the date the draft was written, not a medical review date.
A water-soluble vitamin needed for nucleotide synthesis and one-carbon metabolism. Deficiency causes megaloblastic anaemia and, in early pregnancy, increases the risk of neural tube defects.
Reference interval
| Conventional (ng/mL) | SI (nmol/L) | |
|---|---|---|
| Adults | 3–17 ng/mL | 6.8–38.5 nmol/L |
Specimen: Serum (fasting, protect from light and haemolysis) · Conventional × 2.266 = SI
Causes of high values
Folic acid supplementation or fortified foods, B12 deficiency (the methyl-folate trap), recent food intake, bacterial overgrowth of the small bowel.
Causes of low values
Poor diet (alcohol use disorder, malnutrition), malabsorption (coeliac disease), increased requirements (pregnancy, haemolysis), drugs (methotrexate, trimethoprim, phenytoin).
Pre-analytical and method notes
Serum folate reflects recent intake and rises quickly after a meal, whereas red-cell folate reflects longer-term stores but has poorer standardisation. Haemolysed samples falsely raise the result, and the deficiency threshold quoted (about below 3 ng/mL or 7 nmol/L) varies by method. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity (WHO/NMH/NHD/MNM/11.1). World Health Organization (2011) — Tier 1 (standards / international bodies)
References are listed only where the article cites them. See the sources page for the full policy. How sources are chosen and credited