Selenium Biomarker Testing
A selenium test measures your selenium status to help evaluate deficiency or excess and guide follow-up labs, with easy ordering through Vitals Vault.
With Vitals Vault, you have access to a comprehensive range of biomarker tests.
Selenium is a trace mineral you need in small amounts, but your body relies on it for important jobs like antioxidant defense and thyroid hormone metabolism.
A selenium lab test helps you see whether your current level looks low, typical, or higher than expected for your situation. That can matter if you have symptoms that overlap with many other issues, if your diet has changed, or if you use supplements.
Because selenium can be both essential and harmful in excess, the goal of testing is not “higher is better.” It is to put your number in context with your health history and related labs so you can make a safer plan with your clinician.
Do I need a Selenium test?
You might consider a selenium test if you are trying to clarify whether a possible nutrient gap is contributing to symptoms such as fatigue, frequent infections, hair or nail changes, or thyroid-related complaints. These symptoms are not specific to selenium, but testing can help you avoid guessing—especially if you are already taking a multivitamin or a standalone selenium product.
Testing is also reasonable if you have a higher likelihood of deficiency because of limited dietary variety, long-term digestive or absorption issues, or a history of bariatric or intestinal surgery. In these situations, selenium can be one piece of a broader micronutrient picture.
On the other side, you may want testing if you suspect you are getting too much selenium. That can happen when you stack supplements (for example, a multivitamin plus a “thyroid support” product) or use high-dose selenium for a prolonged period.
A selenium result is best used to support clinician-directed care and follow-up testing, not as a standalone diagnosis or a reason to self-treat.
Selenium is typically measured on a blood sample (often serum) in a CLIA-certified laboratory; results should be interpreted alongside symptoms, diet, and related labs.
Lab testing
Ready to order a selenium test or plan a retest?
Schedule online, results typically within about a week
Clear reporting and optional clinician context
HSA/FSA eligible where applicable
Get this test with Vitals Vault
If you want a clear selenium number without a long wait, Vitals Vault lets you order lab testing and complete your blood draw through a national lab network. You can use your result to have a more focused conversation with your clinician, especially if you are weighing whether to change diet, stop a supplement, or retest after an adjustment.
After your results post, PocketMD can help you understand what “low,” “in range,” or “high” might mean for you, and which companion labs often add clarity (for example, thyroid markers or other trace minerals). That way, you are not left trying to interpret a single micronutrient in isolation.
If your result suggests a potential issue, you can also use Vitals Vault to reorder selenium later to confirm a trend, or to add broader panels when you and your clinician want a more complete map of nutrition and metabolism.
- Order online and complete your draw at a local lab location
- PocketMD helps you interpret results and plan sensible follow-ups
- Easy retesting to confirm changes over time
Key benefits of Selenium testing
- Helps identify possible selenium deficiency when symptoms and diet history raise concern.
- Helps detect excess selenium exposure, which can occur from stacked supplements or high-dose use.
- Adds context for thyroid-related symptoms because selenium supports enzymes involved in thyroid hormone metabolism.
- Supports a safer supplement plan by showing whether you likely need selenium at all before increasing intake.
- Provides a baseline you can retest after diet or supplement changes to confirm that your level is moving in the right direction.
- Pairs well with other micronutrient and thyroid labs to reduce “single-marker” guesswork.
- Gives you a concrete number you can review with PocketMD and your clinician to decide on next steps.
What is Selenium?
Selenium is an essential trace mineral. Your body incorporates it into proteins called selenoproteins, many of which help manage oxidative stress and support immune and thyroid function.
In the thyroid, selenium is involved in enzymes (deiodinases) that help convert thyroid hormone into its active and inactive forms. Selenium is also part of antioxidant systems (such as glutathione peroxidases) that help protect cells from damage.
A selenium test measures the amount of selenium in your blood (most commonly serum). It is a snapshot of status that can be influenced by recent intake, overall nutrition, inflammation, and supplementation. Because different labs may use different methods and reference intervals, it is important to interpret your value using the ranges provided on your report and in the context of your overall health.
Serum vs. other ways to assess selenium
Serum selenium is commonly used and widely available. In some clinical situations, other specimens (such as whole blood) may be used to reflect longer-term status, but availability and interpretation vary. If you are monitoring a change over time, try to use the same specimen type and lab method when possible so your results are more comparable.
Why “more” is not always better
Selenium has a relatively narrow window between too little and too much. If you supplement without knowing your baseline, it is possible to overshoot, especially when multiple products contain selenium. Testing helps you aim for an appropriate range rather than chasing a high number.
What do my Selenium results mean?
Low selenium levels
A low selenium result can suggest inadequate intake, reduced absorption, or increased needs. If you also have other nutrient abnormalities, the pattern may point toward a broader nutrition or malabsorption issue rather than selenium alone. Your clinician may ask about diet, gastrointestinal symptoms, surgeries, or restrictive eating, and may recommend checking related markers before deciding on supplementation.
Optimal (in-range) selenium levels
An in-range selenium result generally means your current intake and absorption are meeting your body’s needs. If you are taking selenium supplements and your level is comfortably in range, it may be a sign that you do not need higher dosing and that “maintenance” (or stopping extra selenium) could be reasonable to discuss. If you still have symptoms, it is worth looking for other explanations rather than assuming selenium is the driver.
High selenium levels
A high selenium result most often reflects excess intake, usually from supplements or fortified products. Persistently high levels can raise concern for selenium excess (sometimes called selenosis), which may be associated with symptoms such as nausea, gastrointestinal upset, hair loss, brittle nails, or a metallic taste. If your result is high, do not increase selenium further, and review all supplements and nutrition products with your clinician to identify hidden sources.
Factors that influence selenium
Recent supplement use can raise selenium levels and may be the biggest reason results run high. Diet patterns matter too because selenium content varies by food source and geography, so two people eating “similar” foods can have different intake. Inflammation, acute illness, and overall protein status can also shift blood measurements and make a single result harder to interpret. For trend tracking, retest under similar conditions and share medication and supplement lists with the ordering clinician.
What’s included
- Selenium
Frequently Asked Questions
Do I need to fast for a selenium blood test?
Fasting is not always required for selenium, but your ordering instructions may vary based on the lab and whether selenium is bundled with other tests that do require fasting. If you are trending selenium over time, using similar conditions (time of day, fasting status, and supplement timing) can make comparisons more meaningful.
Should I stop supplements before a selenium test?
If you take selenium (or a multivitamin that contains it), ask your clinician whether to hold it before testing. Taking selenium shortly before a blood draw can influence your result, and the right approach depends on whether you are checking baseline status or monitoring your current regimen.
What is a normal selenium level?
“Normal” depends on the lab method and the reference interval printed on your report. Instead of comparing your number to an online range, use the range provided by your lab and interpret it with your clinician, especially if you have symptoms or you are supplementing.
Can high selenium be dangerous?
Yes, selenium can be harmful in excess, particularly with long-term high intake from supplements. A high lab result is a reason to review all sources of selenium and avoid increasing your dose until you have a plan with your clinician.
How long does it take to fix low selenium?
The timeline depends on why it is low and what changes you make. If low selenium is due to low intake, levels may improve over weeks after diet or supplement adjustments, but your clinician may recommend retesting to confirm the change rather than assuming it worked.
How often should I retest selenium?
If you are correcting a low level or backing off supplements after a high level, retesting is often done after a reasonable adjustment period so your body can reach a new steady state. Your clinician can suggest timing based on your starting value, symptoms, and whether other nutrition issues are being addressed at the same time.