Functional Medicine Testing and Treatment Plans: What Is Commonly Ordered and Why It Matters
What tests and plans are commonly described in functional medicine, what each test is legitimately used for, what research found about the marketed uses, and questions to ask about cost.
Content last updated . This page has not been medically reviewed.
Information only, not medical advice. For emergencies call 911 (in the US). This page never tells you to order a test or start a diet or supplement. Do not stop or change prescribed medicines, including thyroid, diabetes or blood-pressure medicines, because of a test result without your prescriber.
Why testing matters in this model
Functional medicine, as reviewers describe it, seeks individualized "root causes" using systems-based assessment and nonstandard laboratory testing. [1] A test result can change what you eat, take or spend, and can also start a chain of further tests. The same review warns that its diagnostic strategies "may contribute to low-value testing, care cascades, and health inequities". [1] So this page asks of each test: what is it legitimately used for, and what did research find about the use being marketed? For the model itself see what functional medicine is and what the evidence shows.What care plans are described as including
In the studies we read, plans combined lifestyle change, elimination diets, health coaching and tailored dietary supplements alongside usual care. [2] [3] [4] A published case report, as described by critics, relied on a comprehensive stool analysis and a nutritional evaluation from one commercial laboratory. [5] We do not describe diet or supplement protocols. Ask what is being recommended, why, what it costs and whether the clinic sells it; see supplements and vitamins dispensed in integrative practice.Tests checked
| Test | What medicine legitimately uses it for | What we read about the marketed use | Label |
|---|---|---|---|
| Reverse T3 (a thyroid-related blood test) | Controversial clinical utility, according to the authors of a laboratory study. [6] | In one national laboratory's data, 60 of the 100 highest-volume orderers of reverse T3 were classified as functional medicine practitioners, and a systematic review found little evidence supporting high volumes. [6] | Insufficient evidence |
| Food-specific IgG or IgG4 "sensitivity" panels | Food allergy testing measures IgE antibodies or uses skin tests under an allergist. [7] | A European allergy task force said food-specific IgG4 does not indicate allergy or intolerance and should not be performed for food complaints. [8] The NHS says some tests you can buy for food intolerance are not recommended. [9] | No good evidence of benefit for this use |
| Hair mineral analysis | Not described in the abstract we read as a recognized clinical assessment. | A JAMA study sent a split hair sample from one volunteer to six laboratories; results differed more than 10-fold for 12 minerals and the authors called the analysis unreliable. [10] | No good evidence of benefit |
| Saliva or blood cortisol for "adrenal fatigue" | MedlinePlus: cortisol tests help diagnose or rule out conditions causing too much or too little cortisol. [11] | A systematic review found no substantiation that "adrenal fatigue" is an actual medical condition. [12] | Marketing claim for the "fatigue" label |
| Direct-to-consumer microbiome or stool analyses | Research tool that has spread into practice. [13] | A narrative review says many companies offer analyses "of dubious quality and/or as a business appliance aimed at selling supplements and the like". [13] | Insufficient evidence for guiding treatment |
Each has its own page: food IgG tests, hair mineral analysis, saliva cortisol and "adrenal" tests, stool and microbiome tests and the broader tests sold in integrative practice.
A normal-range or abnormal result is not a diagnosis. MedlinePlus notes a cortisol test alone cannot diagnose the cause of abnormal levels, and usually more tests follow. [11] We did not verify that any individual clinic orders these tests, only that they are discussed in sources about functional-style and integrative testing.
Questions to ask about any plan
- What will this test or step tell us that changes my treatment? What happens if the result is normal?
- Is this test accepted in medical guidelines for my problem, or is it specialty or research testing?
- What does each test, visit and supplement cost, in writing, and will insurance cover it? (We could not verify prices; none are given.)
- Does the clinic sell the supplements it recommends?
- Will my regular doctor receive the results, and who reviews my medicines for interactions?
More: lab tests ordered in integrative practice, how to evaluate a proposed treatment plan and second opinions and sharing records.
Frequently asked questions
What tests does functional medicine use?
Sources describe heavy use of specialized laboratory tests, including stool and nutritional panels, though practice varies by clinic. [1] [5]
Are functional medicine lab tests accurate?
It depends on the test. Hair mineral results varied widely between laboratories in one study, and food IgG4 testing is not recommended by an allergy task force. [10] [8]
Is a reverse T3 test useful?
A laboratory study found little evidence to support high volumes of reverse T3 orders. [6] Talk to your prescriber before changing any thyroid medicine.
Are home test kits for food sensitivity reliable?
The NHS says some purchasable tests that claim to diagnose food intolerance are not recommended and may lead people to avoid multiple foods. [9]
Will insurance pay for functional medicine tests?
Proper evidence not found. We searched PubMed and the clinic page we read and found no coverage statement; ask your insurer. The Yale and NYU review notes substantial out-of-pocket costs. [1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Who should check with a clinician first
References
- Drawing a line between integrative and functional medicine. Am J Med. 2026 (review by authors at Yale School of Medicine and NYU Grossman School of Medicine; abstract read). Read 2026-10-22.
- A functional medicine approach to diabetes control and quality of life: an open-label randomized pilot study. J Clin Transl Endocrinol. 2026 (Cleveland Clinic and Case Western Reserve authors). Read 2026-10-22.
- Functional medicine health coaching improved elimination diet compliance and patient-reported health outcomes: Results from a randomized controlled trial. Medicine (Baltimore). 2024 (authors include University of Maryland and the Institute for Functional Medicine). Read 2026-10-22.
- Strobel TM, et al. Functional Medicine Approach to Patient Care Improves Sleep, Fatigue, and Quality of Life in Patients With Inflammatory Bowel Disease. Crohns Colitis 360. 2022. Read 2026-10-22.
- Bellamy J. AAFP: Functional Medicine lacks supporting evidence; includes "harmful" and "dangerous" treatments. Science-Based Medicine, October 26, 2017 (a critical commentary; it quotes the Institute for Functional Medicine). Read 2026-10-22.
- Does Reverse Triiodothyronine Testing Have Clinical Utility? An Analysis of Practice Variation Based on Order Data from a National Reference Laboratory. Thyroid. 2018 (University of Utah and USC authors). Read 2026-10-22.
- MedlinePlus. Food Allergy Testing. Read 2026-10-22.
- Stapel SO, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Allergy. 2008. Read 2026-10-22.
- NHS (UK). Food intolerance. Read 2026-10-22.
- Seidel S, et al. Assessment of commercial laboratories performing hair mineral analysis. JAMA. 2001. Read 2026-10-22.
- MedlinePlus. Cortisol Levels Test. Read 2026-10-22.
- Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. 2016. Read 2026-10-22.
- How to navigate the many direct-to-consumer microbiota analyses and why to use them. Minerva Gastroenterol (Torino). 2025 (narrative review). Read 2026-10-22.