LAB RESULTS

What does a functional medicine doctor test for, and what do the results mean?

The standard blood work and the specialty tests functional medicine practitioners often order, which ones have solid evidence, and how results can shape a supplement routine.

The short version

Functional medicine visits usually start with standard blood work: vitamin D, ferritin and an iron panel, B12 and folate, A1C, a lipid panel, thyroid tests and inflammation markers. These are the tests with the best evidence behind them.
Many practitioners add specialty tests, such as IgG food sensitivity panels, stool microbiome reports and hair mineral analysis. These are much less reliable for guiding supplements.
European allergy experts advise against IgG food testing: IgG to a food mostly shows you have eaten it, not that it bothers you.
A 2001 JAMA study sent the same hair sample to 6 labs and got conflicting results for nearly every mineral, and a 2026 study found home stool microbiome tests varied widely between companies.
Use a result to change a decision, like whether to take iron or how much vitamin D, and give any change a couple of months before you retest. Apiece doesn't order labs, but you can add recent results and the amounts in your formula adjust to them.

What tests does a functional medicine doctor usually order?

Most functional medicine workups combine a long health history with two groups of tests: standard blood work any clinician could order, and specialty tests sold by private labs. The first group has decades of research behind it. The second group varies a lot in quality.

Functional medicine is an approach that looks for the drivers behind symptoms. The model itself has limited research: a 2019 Cleveland Clinic study found modest gains in self-reported quality of life, but it was observational, so it cannot show the approach caused them.

So the useful question for any test is simple: is it accurate, and would the result change what you do?

Which standard blood tests are most useful for supplements?

The standard tests that most often change a supplement decision are:

25-hydroxy vitamin D: the usual measure of vitamin D status from sun, food and supplements.
Ferritin with an iron panel: ferritin reflects iron stores, and a level below 30 mcg/L suggests low iron. Ferritin also rises with inflammation, so a normal value can hide low stores.
Vitamin B12, with methylmalonic acid if B12 is borderline: worth checking if you eat little animal food, are older, or take metformin or acid-reducing medicines.
Folate: serum folate reflects recent intake; red blood cell folate reflects a longer stretch.
A1C or fasting glucose and a lipid panel: these help set priorities if heart and metabolic health is a goal.
TSH: a thyroid function screen, not a number to steer with supplements.

Serum magnesium is common but weak: less than 1% of the body's magnesium is in serum, and those levels are kept under tight control, so a normal result doesn't show your stores.

Are IgG food sensitivity tests accurate?

No. A European Academy of Allergy and Clinical Immunology task force concluded that food-specific IgG4 testing is irrelevant for working up food allergy or intolerance and should not be done for food-related complaints.

The reason is that IgG antibodies to a food are a normal sign your immune system has met that food repeatedly, and they are often present with no symptoms at all. A long list of positive foods mostly mirrors what you eat. Cutting many foods based on these panels can make a diet narrower and harder to get enough nutrients from. If you suspect a food, a structured elimination and reintroduction plan with a clinician or dietitian is a better guide.

Can hair mineral analysis show nutrient levels?

Not reliably. In a 2001 JAMA study, researchers split one healthy volunteer's hair sample and sent it to 6 US labs that together handle about 90% of hair mineral testing. For 12 minerals, the highest and lowest results differed more than 10-fold.

The labs' normal ranges also differed so much that nearly every mineral was labeled high, normal or low depending on the lab, and their supplement suggestions conflicted. The authors recommended that clinicians not use hair analysis to judge nutritional status. Blood tests such as ferritin, B12 and vitamin D are the better tools.

What can a stool or gut microbiome test tell you?

Less than the reports suggest, at least for now. A 2026 study from the US National Institute of Standards and Technology sent the same standardized stool material to 7 direct-to-consumer gut microbiome services. Results differed so much that the gap between companies was about as large as the natural difference between different people.

An international expert consensus published in 2025 also noted that evidence for the clinical usefulness of microbiome testing is scarce and that consumer tests are sold without proven value in practice. That doesn't mean gut health doesn't matter. It means a microbiome report is a shaky basis for choosing a probiotic or a list of supplements. Standard stool tests a doctor orders for specific symptoms, such as checks for infection or blood, are a different matter.

Should healthy people test their vitamin D?

Not routinely, according to the Endocrine Society. Its 2024 guideline suggested against routine 25-hydroxy vitamin D testing for the general population without a specific reason, because trials have not defined a target level that clearly improves outcomes for most people.

Testing still makes sense when there is a reason: very little sun, darker skin at high latitudes, conditions or medicines that affect absorption, or when you want to know whether a dose is too high. The point is that more tests are not automatically better. Each one should answer a question you actually have.

How do lab results shape a supplement routine?

Good results change three things: whether you take a nutrient at all, how much, and when to check again.

Low ferritin can justify iron for a set period; normal or high ferritin is a reason to leave iron out, since more is not better.
A low or borderline B12 with high methylmalonic acid supports adding B12.
A vitamin D result helps set a dose that fits you and stays under the adult upper limit.
Lipid, A1C and thyroid results don't point to one supplement, but they help set priorities with your clinician.

Nutrient levels take time to settle after a change, so ask your clinician when to retest; many wait a couple of months. Apiece doesn't order labs, but if you add recent results, your formula's amounts adjust to them, and it stays at 10 capsules a day or fewer.

What should you ask before paying for a specialty test?

A few questions protect your time and money:

What decision will this result change?
Has this test been shown to be accurate and repeatable in published research?
Is it covered by insurance, and is there a standard test that answers the same question?
Does the lab that runs the test also sell the supplements it recommends?

Tell whoever orders your labs about everything you take. High-dose biotin, for example, can interfere with some lab tests, which the FDA has warned about. And check with your own doctor or pharmacist before starting supplements if you take medications, are pregnant or have a health condition.

Questions

What blood tests does a functional medicine doctor order?

Commonly a broad panel: vitamin D (25-hydroxy), ferritin and an iron panel, B12 and folate, A1C or fasting glucose, a lipid panel, thyroid tests such as TSH, and inflammation markers. Many also add specialty tests from private labs, which vary much more in reliability.

Are food sensitivity tests worth it?

IgG food sensitivity panels are not a reliable guide. A European allergy task force advised against them because IgG to a food mainly reflects that you have eaten it. A structured elimination and reintroduction plan with a clinician or dietitian is a better way to test a suspected food.

Is hair mineral analysis accurate?

No. When one hair sample was split and sent to 6 commercial labs, results for 12 minerals differed more than 10-fold and the labs labeled minerals high, normal or low inconsistently. Researchers recommended against using it to judge nutritional status.

Do I need lab work before taking supplements?

Not always. Testing is most useful when it changes a decision, such as whether to take iron or how much vitamin D to take. The Endocrine Society suggests against routine vitamin D testing in healthy people without a specific reason.

How often should I recheck my labs after starting supplements?

Nutrient levels take time to settle after a dose change, so retesting within a few weeks rarely gives a fair read. Ask your clinician when a recheck makes sense for you; many wait a couple of months.

Can I use my lab results with Apiece?

Yes. Apiece doesn't order labs, but you can add recent results when you build your formula and the amounts adjust to them. Share your results and your supplement list with your own doctor too.

Sources

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*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This page is general information, not medical advice. Check with your doctor or pharmacist before starting a supplement, especially if you take medication, are pregnant or nursing, or have a health condition. Updated 2026-10-23.