Vitamin D and B12 Blood Tests Explained: Who Needs Them in Palm Beach County, FL

What it involves

Both tests are simple blood draws that measure a vitamin in your blood. MedlinePlus says a vitamin D test measures vitamin D, which helps the body absorb calcium for bones and teeth, while a vitamin B12 test measures the B12 your nerves and blood cells need. Neither is recommended for everyone, and the useful question is whether you have a reason to be tested.

Who this is for

• Patients with bone pain, muscle weakness, or low bone density that a provider wants to explain
• Patients with numbness, tingling, or balance trouble that could involve B12
• Patients who take medicines or have digestive conditions that affect how vitamins are absorbed
• Patients who were told a vitamin level was low and want to understand the follow-up

What to expect

• A review of your symptoms, diet, sun exposure, medicines, and supplements
• A blood draw from a vein in your arm, with fasting only if your provider asks for it
• A plain explanation of what your level means and whether more testing is needed
• A plan, which may include supplements or food changes, and a date to recheck

How the vitamin D test works

MedlinePlus says you get vitamin D from sunlight, a few foods such as egg yolks and fatty fish, fortified foods, and supplements. Most vitamin D blood tests measure a form called 25(OH)D, which MedlinePlus calls the most accurate way to tell whether you have enough. The result is usually labeled deficient, insufficient, sufficient, or possibly toxic, and total vitamin D is the number that matters. Vitamin D matters for bones as well, and the osteoporosis and bone density guide explains how calcium and vitamin D fit into bone health.

Who may need a vitamin D test

MedlinePlus says routine vitamin D testing is not recommended for everyone. A provider may order it for people with conditions linked to deficiency, such as soft bones or osteoporosis, or with bone pain, muscle weakness, or fractures. Higher-risk groups include people who rarely get sun on bare skin, people with weight loss surgery, people with Crohn disease, celiac disease, or kidney or liver disease, and people taking certain medicines such as steroids. Numbness and tingling in the hand can also come from a squeezed nerve at the wrist rather than a vitamin level, as the carpal tunnel and wrist pain guide explains.

Why kidney and liver health come up

MedlinePlus explains that the body must convert vitamin D into a usable form with the help of the liver and kidneys, so a low result can sometimes be a sign of kidney or liver disease. That is one reason a provider may look at related results, such as those explained in the kidney function tests guide, instead of treating a low number as a simple supplement problem.

How the vitamin B12 test works

MedlinePlus says a B12 level is most often checked when other blood tests suggest megaloblastic anemia, including pernicious anemia, or when there are nerve symptoms such as numbness or tingling in the arms and legs, weakness, and loss of balance. It lists normal values of 299 to 1054 pg/mL and notes that ranges can differ slightly between laboratories, so compare your result with the range printed on your own report.

Common reasons for a low B12

MedlinePlus lists causes of low B12 as too little in the diet, which it calls rare except with a strict vegetarian diet, diseases that interfere with absorption such as celiac and Crohn disease, a lack of intrinsic factor, and pregnancy. It also lists medicines that can affect the result, including metformin and proton pump inhibitors. Tell your provider what you take, and do not stop any of it on your own. Low B12 is one cause of anemia, though iron shortage is the most common kind, as the anemia and low iron guide explains. Low B12 is one of the vitamin deficiencies MedlinePlus lists among the causes of numbness and tingling, and the numbness and tingling guide shows where that fits.

Preparing and following up

MedlinePlus says no special preparation is needed for a vitamin D test, while a B12 level may need fasting for about six to eight hours. If you are also having other tests, read the fasting blood work preparation guide first. Thyroid problems can cause some of the same symptoms, so the thyroid blood tests guide is worth a look if tiredness is the main complaint.

Sources

• MedlinePlus — Vitamin D Test
• MedlinePlus — Vitamin B12 Level