Folate (Folic Acid): Normal Range, What High & Low Levels Mean

A folate blood test measures how much vitamin B9 — also called folate or folic acid — is present in the liquid part of your blood (your serum or plasma). Folate is essential for building and repairing DNA, supporting cell division, and producing healthy red blood cells. When your doctor orders this test, they're checking whether your body has enough of this nutrient to carry out those core functions. It's commonly used to investigate unexplained tiredness or anaemia, to check nutritional status, and to monitor levels in people whose health conditions or medications may affect folate. Discuss what your specific result means in the context of your health with your healthcare provider.

For adults, Mayo Clinic Laboratories sets the reference range for serum folate between 2.7 and 17 ng/mL (nanograms per milliliter). A result within this range generally suggests your folate levels are sufficient to support normal DNA synthesis and red blood cell production. Keep in mind that reference ranges can vary slightly between different laboratories depending on the equipment and methods they use, so always compare your result against the range printed on your own lab report. A number inside the reference range doesn't automatically rule out a problem, nor does a number just outside it mean something is seriously wrong. Your healthcare provider is best placed to interpret your specific result.

The most common reason for a folate result above 17 ng/mL is folic acid supplementation — taking a multivitamin or a standalone folic acid supplement regularly can push levels higher than the reference range. A diet very rich in folate foods, such as leafy greens and legumes, can also contribute. There is one less obvious cause worth understanding: vitamin B12 deficiency can make serum folate appear elevated because, without adequate B12, folate cannot enter your cells properly and accumulates in the bloodstream instead. This means a high folate result alongside certain symptoms could still point to a nutritional issue. Your healthcare provider can order additional tests to get the full picture.

Several factors can push folate below 2.7 ng/mL. The most straightforward is a diet low in folate-rich foods like leafy greens, legumes, and fortified grains. Alcohol use disorder is another significant cause because alcohol both impairs folate absorption and increases how quickly the body excretes it. Digestive conditions such as celiac disease or Crohn's disease can prevent proper absorption. Pregnancy raises the body's folate demand considerably, making deficiency more likely if intake doesn't increase. Certain medications — including methotrexate, phenytoin, trimethoprim, and sulfasalazine — can also reduce folate levels, as can haemolytic anaemia and chronic dialysis. Talk to your healthcare provider about which factors may be relevant to your result.

Low folate can produce a range of symptoms, many of which overlap with other nutritional deficiencies. Persistent fatigue and weakness are among the most common. You might also notice pale skin, shortness of breath, or a rapid heartbeat — signs that your red blood cells aren't carrying oxygen as efficiently as they should (a pattern called megaloblastic anaemia). A sore, red, or swollen tongue (known as glossitis), mouth ulcers, and pins-and-needles sensations can also occur. Some people experience irritability or difficulty concentrating. In early pregnancy, low folate is associated with neural tube defects in the developing baby. High folate from supplements typically causes no noticeable symptoms. Please discuss any symptoms you're experiencing with your healthcare provider.

A folate blood test result is valuable information, but it's just one piece of a larger picture. Whether supplementation makes sense for you depends on your result, your symptoms, your diet, any medications you take, your digestive health, and — if relevant — whether you are pregnant or planning to become pregnant. Taking supplements without guidance can sometimes mask other deficiencies; for example, very high supplemental folate can hide neurological symptoms caused by a vitamin B12 deficiency. For that reason, self-prescribing based on a number alone isn't a reliable approach. Your healthcare provider can review your full results and personal circumstances to recommend the most appropriate next step for your situation.