Doctors may order a B12 blood test for several reasons. Vitamin B12 is an essential nutrient that helps keep the body’s nerve and blood cells healthy and helps make DNA. A B12 deficiency can cause serious problems, so doctors test B12 levels to check for deficiencies and related disorders.
What is Vitamin B12?
Vitamin B12 is a water-soluble vitamin that is naturally present in some foods and available as a dietary supplement. It helps keep the body’s nerve and blood cells healthy and helps make DNA.
Vitamin B12 has several important functions:
- Helps make red blood cells and keep the nervous system working properly
- Needed to make DNA
- Plays a role in metabolizing food and using folic acid
- May help prevent megaloblastic anemia
- Needed for cardiovascular and cognitive health
There are several different forms of vitamin B12 in foods and supplements. The two main forms are:
- Cyanocobalamin: This form can be converted to active B12 forms in the body. It is used in supplements and fortified foods.
- Methylcobalamin: This form is readily usable by the body. It is found naturally in foods.
Good food sources of B12 include:
- Beef liver
- Clams
- Trout
- Salmon
- Tuna
- Crab
- Yogurt and milk (if fortified)
- Eggs
- Fortified cereals
The recommended daily intake of B12 is:
- Infants up to 6 months: 0.4 mcg
- Babies 7-12 months: 0.5 mcg
- Children 1-3 years: 0.9 mcg
- Kids 4-8 years: 1.2 mcg
- Children 9-13 years: 1.8 mcg
- Teens 14-18: 2.4 mcg
- Adults: 2.4 mcg
- Pregnant women: 2.6 mcg
- Breastfeeding women: 2.8 mcg
Why Check B12 Levels?
Doctors may order a B12 blood test for the following reasons:
Signs and Symptoms of Deficiency
B12 deficiency can cause a wide range of symptoms, including:
- Fatigue
- Weakness
- Constipation
- Loss of appetite
- Weight loss
- Neurological changes like numbness and tingling in the hands and feet
- Neuropsychiatric symptoms like depression, memory loss, and cognitive decline
- Megaloblastic anemia
If a patient has any of these symptoms, a doctor may check B12 levels to see if a deficiency is causing the problems.
At-Risk Groups
Certain people are at higher risk of B12 deficiency, including:
- Older adults: Some studies show that up to 30% of adults over age 50 may have trouble absorbing naturally occurring vitamin B12.
- People with digestive disorders: Conditions that affect digestion like celiac disease, Crohn’s disease, bacterial overgrowth issues, and chronic pancreatitis can make it harder to absorb B12 from foods.
- People who have had GI surgery: Procedures that remove part of the stomach or small intestine like gastric bypass surgery increase the risk of B12 deficiency.
- Vegetarians or vegans: B12 is naturally found almost exclusively in animal products, so strict vegetarians and vegans are at risk.
- Women with a history of infertility or multiple miscarriages.
- People with diabetes, stroke, or dementia.
- People taking heartburn drugs like proton pump inhibitors.
Doctors may periodically check vitamin B12 levels in these high-risk groups.
Monitoring Treatment
If a patient already knows they have low B12, regular blood tests help monitor if treatment is correcting the deficiency. Doctors can check if supplementation is improving B12 levels and adjust the dose if needed.
How is the B12 Test Performed?
A B12 blood test measures the amount of vitamin B12 in the blood. It requires a blood sample, usually taken by inserting a small needle into a vein in the arm. Some key points about the test:
- No fasting is required. The test can be done anytime.
- Previous B12 supplements or shots can affect results, so doctors may ask about this.
- Results are reported as pg/mL (picograms per milliliter). Normal ranges are typically 200-900 pg/mL.
- Low or borderline levels will prompt further testing for a true deficiency.
- High levels over 1000 pg/mL may indicate liver disease or a blood disorder.
What Do Low B12 Blood Test Results Mean?
If the B12 test comes back low or borderline, the doctor will likely order follow-up testing before diagnosing a true deficiency. This is because the B12 blood test alone can be inaccurate at times. These additional tests help confirm if a deficiency is present:
- Methylmalonic acid (MMA) blood test – Checks MMA levels. MMA levels go up when B12 levels are low.
- Homocysteine levels – Measures homocysteine amino acid levels. High homocysteine indicates low B12.
- Complete blood count – Checks for macrocytic anemia, a possible symptom of B12 deficiency.
- Peripheral smear – Examines blood cell appearance under a microscope for signs of anemia.
- Intrinsic factor antibody test – Helps identify if autoimmune atrophic gastritis is the cause of B12 malabsorption.
If follow-up tests confirm a true B12 deficiency, the doctor will recommend treatment with B12 injections or high-dose oral supplements.
What Are the Causes of B12 Deficiency?
Some potential causes of low B12 levels include:
Dietary Causes
- Inadequate intake – Not eating enough B12-rich animal foods like meat, fish, poultry, eggs, and dairy.
- Vegan or vegetarian diets – Eliminating animal products, the main dietary sources of B12.
Gastrointestinal Causes
- Pernicious anemia – An autoimmune disease where the body attacks intrinsic factor needed for B12 absorption.
- Surgeries or diseases affecting digestion – Such as celiac disease, Crohn’s disease, ulcerative colitis, gastrectomy, gastric bypass, pancreatitis, etc.
- Medications – Certain drugs like proton pump inhibitors can reduce B12 absorption from food.
- Malabsorption syndromes – Conditions preventing proper absorption of nutrients from food.
- Gut bacterial overgrowth – Too much bacteria in the small intestine can use up vitamin B12.
- H. pylori infection – Can sometimes lead to reduced B12 absorption and higher risk of pernicious anemia.
Other Causes
- Heavy alcohol use – Can deplete B12 levels over time.
- HIV/AIDS – Associated with a high risk of B12 deficiency.
- Kidney disease – Reduced kidney function can affect vitamin B12 metabolism.
- Numerous pregnancies – Higher risk of deficiency with multiple pregnancies.
- Breastfeeding – Can deplete B12 levels without adequate maternal intake.
- Inborn errors of B12 metabolism – Rare genetic conditions.
Health Risks of Untreated Vitamin B12 Deficiency
If left untreated, vitamin B12 deficiency can potentially lead to permanent nerve damage and serious medical problems:
- Neurological problems – Damage to the protective myelin sheath surrounding nerves can result in tingling/numbness, muscle weakness, stiff reflexes, balance issues, and cognitive changes like memory loss and confusion.
- Permanent nerve damage – If depleted for a long time, low B12 can cause irreversible nerve injury.
- Anemia – B12 helps make red blood cells. Deficiency can trigger megaloblastic anemia, with symptoms like fatigue and pale skin.
- Birth defects – B12 deficiency in pregnant women may increase the risk of neural tube defects and other problems in babies.
- Psychiatric problems – Low B12 is linked to depression, behavioral disorders, and dementia-like symptoms in some cases.
- Heart disease and stroke – Some research links low B12 with higher cardiovascular disease and stroke risks, potentially due to high homocysteine.
Catching and treating a deficiency early helps prevent permanent damage.
B12 Deficiency Treatment
Treatment for B12 deficiency aims to raise blood levels through supplementation, either with high doses of oral B12 or B12 injections. Patients are often advised to take supplements for life afterward if the deficiency was caused by intrinsic factor antibodies or malabsorption issues.
Oral Vitamin B12 Supplements
High dose oral vitamin B12 supplements can help normalize B12 levels in some patients with dietary deficits or conditions not affecting gut absorption. Typical doses range from 1000-2000 mcg daily of oral cyanocobalamin or methylcobalamin. Supplements are considered just as effective as injections for dietary-related deficiency.
B12 Injections/Shots
For patients with severe deficiencies or conditions affecting absorption like pernicious anemia, B12 shots or injections are usually required to restore adequate B12 levels.
- Initial regimen may involve receiving weekly shots for 1-2 months to rapidly boost B12 stores.
- Maintenance regimen is usually a monthly injection to keep levels adequate long-term.
- Forms used include cyanocobalamin or hydroxocobalamin.
- Some patients learn to self-administer shots at home after proper training.
B12 injections deliver the vitamin directly into the bloodstream, bypassing potential absorption issues. Response to treatment is typically monitored with periodic blood tests to ensure levels are being maintained.
Supplementing Carefully
While generally considered safe at recommended doses, there are some things to keep in mind with B12 supplementation:
- Sensitivities to high doses – Some people report side effects like skin rashes, itchiness, and digestive upset from excessive supplementation.
- Masking symptoms – High doses may alleviate neurological symptoms without addressing an underlying condition, so should be used under a doctor’s guidance.
- Interactions with medications – Very high B12 intake may interact with some cancer drugs like chlorambucil and seizures meds like phenytoin.
Unless remedying a known deficiency, it’s best not to exceed the 2.4-2.8 mcg daily tolerable upper intake level. Always talk to a doctor before beginning B12 injections or high-dose supplements.
Preventing B12 Deficiency
People can help maintain adequate B12 levels by:
- Eating B12-rich foods like animal products, fortified grains, and supplements if vegetarian/vegan.
- Treating conditions known to impair absorption like H. pylori infections or gut disorders.
- If over age 50, considering supplements or periodic screening for deficiency.
- Avoiding things that deplete B12 like heavy alcohol use and proton pump inhibitor drugs long-term when possible.
Getting enough B12 helps prevent deficiency. Doctors may recommend supplementation or injections for those at increased risk due to their age, diet, or medical conditions.
Conclusion
In summary, doctors order a vitamin B12 blood test to check levels and screen for deficiency. Low B12 causes symptoms like fatigue, weakness, neurological changes, and megaloblastic anemia. B12 deficiency is more common in older adults, vegetarians, and people with absorption disorders. Left untreated, it can potentially lead to permanent neurological damage. However, it’s easily correctable through supplementation. B12 testing helps identify people who may benefit from high dose supplements or injections to recover their levels and maintain long term health.