The most reliable way to find out which vitamins you’re low in is through a blood test ordered by your doctor or purchased directly from a lab. There’s no single test that covers every nutrient, so what gets checked depends on your symptoms, risk factors, and what you ask for. Here’s how the process works and what to expect.
What a Standard Blood Test Covers
A routine blood panel at your annual physical doesn’t automatically check vitamin levels. Basic metabolic panels measure things like blood sugar, kidney function, and electrolytes, but they skip most vitamins entirely. If you want to know your nutrient status, you need to specifically request it or have a reason that prompts your doctor to order it.
The most commonly tested nutrients are vitamin D, vitamin B12, iron (usually as part of a complete blood count or iron panel), and folate. These are the ones doctors check most often because deficiencies are relatively common and the tests are well established. Vitamin D alone is one of the most frequently ordered lab tests in the country. Beyond those, your doctor can also test for vitamins A and C, zinc, selenium, magnesium, thiamin (B1), and copper, though these are typically ordered only when there’s a specific clinical concern.
Comprehensive micronutrient panels that test a wide range of vitamins and minerals at once do exist. Labcorp, for example, offers a micronutrient test for $239 and a more detailed custom panel for $485, both payable with HSA or FSA funds. These don’t require a doctor’s visit, though a provider reviews your order before the lab runs it. If your insurance covers the testing, it’s usually because your doctor documented a medical reason for it, such as symptoms or a condition that raises your risk.
What the Numbers Actually Mean
When results come back, each nutrient is reported with a reference range. Understanding where you fall matters more than just glancing at whether something is flagged as “low.”
For vitamin D, levels are measured in nanograms per milliliter. Normal is 30 to 100 ng/mL. Between 20 and 30 is considered insufficient, meaning you’re not critically low but not where you should be. Between 10 and 20 qualifies as deficient, and anything below 10 is severely deficient. For vitamin B12, levels below 200 pg/mL are considered low, with a normal range of 200 to 900 pg/mL.
One important wrinkle: blood levels don’t always reflect what’s happening inside your cells. Inflammation, infection, dehydration, and even the time of day you get your blood drawn can shift results. Iron, selenium, zinc, thiamin, folate, B12, and vitamins A, C, and D all show lower plasma concentrations during inflammatory states. Copper is the exception and actually rises during inflammation. This means that if you’re sick or dealing with a flare-up of a chronic condition, your results may look worse than your true baseline. Your doctor should interpret the numbers in context, not in isolation.
Signs That Suggest a Deficiency
Sometimes your body gives you clues before a blood test confirms anything. The challenge is that most vitamin deficiency symptoms are vague and overlap with dozens of other conditions.
Persistent fatigue, shortness of breath, and dizziness are classic signs of vitamin deficiency anemia, which can result from low B12, folate, or iron. Pale or yellowish skin is another indicator, though this can be harder to spot on darker skin tones. B12 deficiency specifically can cause numbness or tingling in the hands and feet, muscle weakness, unsteady movements, and changes in mood or thinking. These neurological symptoms tend to appear when a deficiency has been present for a while.
Vitamin D deficiency often shows up as bone pain, muscle weakness, or frequent illness. Magnesium deficiency can cause muscle cramps, poor sleep, and irritability. Iron deficiency may cause brittle nails, cold hands and feet, and cravings for non-food items like ice. None of these symptoms on their own confirm a deficiency, but a cluster of them gives your doctor a reason to test.
Who Should Get Tested
Medical guidelines don’t recommend blanket vitamin screening for everyone. The U.S. Preventive Services Task Force has stated that there isn’t enough evidence to recommend routine vitamin D screening for healthy, non-pregnant adults with no symptoms. The Endocrine Society takes a slightly different position and recommends screening people who are at elevated risk.
You’re more likely to benefit from testing if you fall into one of these groups:
- Digestive conditions: Celiac disease, Crohn’s disease, ulcerative colitis, chronic pancreatitis, and small intestinal bacterial overgrowth (SIBO) all interfere with nutrient absorption. Liver disease reduces the body’s ability to process fat-soluble vitamins. Anyone with a diagnosed malabsorption condition should have their levels monitored regularly.
- Surgical history: Gastric bypass, ileal resection, or other surgeries that remove or bypass sections of the intestine reduce your absorptive surface area permanently.
- Dietary restrictions: Strict vegan or vegetarian diets raise the risk of B12 deficiency specifically, since B12 occurs naturally only in animal products. Very restrictive diets for any reason can create gaps.
- Medications that deplete nutrients: Several common prescriptions quietly drain specific vitamins and minerals over time. Proton pump inhibitors (heartburn drugs like omeprazole) lower B12, vitamin C, iron, calcium, magnesium, and zinc. Metformin, widely prescribed for type 2 diabetes, reduces B12 and can affect calcium and vitamin D. Birth control pills lower B6, B12, folate, magnesium, and vitamins C and E. Loop and thiazide diuretics (blood pressure medications) deplete magnesium, potassium, and zinc. Even long-term SSRI antidepressant use is associated with lower folate and reduced calcium and vitamin D.
- Age over 65: Older adults absorb B12 less efficiently and are at higher risk for vitamin D deficiency due to less sun exposure and reduced skin synthesis.
- Pregnancy or planning pregnancy: Folate, iron, and vitamin D needs increase significantly.
At-Home Test Kits vs. Lab Draws
At-home finger-prick kits from companies like Everlywell, LetsGetChecked, and others let you collect a small blood sample and mail it to a lab. These are convenient, but the question is whether they’re accurate enough to trust.
A review of 29 self-testing kits found that most participants were able to perform the tests correctly and get results that correlated well with those from professional lab draws. That said, finger-prick samples yield a smaller volume of blood, which limits how many nutrients can be tested at once and can introduce more variability. For a basic check of vitamin D or B12, an at-home kit is a reasonable starting point. For a comprehensive look at multiple nutrients, a venous blood draw at a lab is more reliable and gives your provider more data to work with.
What To Do With Your Results
Getting a number back is only the first step. What matters is building a plan that actually corrects the deficiency, and that plan looks different depending on how low you are and why.
Mild insufficiencies can often be addressed through dietary changes alone. A registered dietitian can assess your eating patterns, identify gaps, and build a personalized nutrition plan that accounts for your food preferences, any dietary restrictions, and existing health conditions. This is more precise than guessing which supplement to buy off a shelf. Dietitians use a structured process: they evaluate your intake, set targets for energy and specific nutrients, recommend foods and meal timing, and follow up to see if levels improve.
When diet alone isn’t enough, supplements fill the gap. Your doctor or dietitian can recommend the right form and dose. This matters because not all supplement forms are equally well absorbed, and taking too much of certain fat-soluble vitamins (A, D, E, K) can cause toxicity. Iron supplements, for instance, are absorbed better on an empty stomach with vitamin C, but they cause nausea in many people, so the timing and form need to be tailored to what you’ll actually stick with.
If a malabsorption condition is behind your deficiency, correcting it may require higher doses, different delivery methods, or treating the underlying digestive issue first. Retesting after 8 to 12 weeks of supplementation is standard practice to confirm that levels are actually improving.