Functional medicine tests: what the evidence actually says
Which functional tests have evidence behind them?
DUTCH (dried urine hormone test)
Limited evidenceWhat it can tell you
Levels of hormone breakdown products in urine.
What it can't tell you
A validated diagnosis for any fatigue, hormone or menstrual condition. No independent studies show it improves outcomes.
Worth knowing: The main published validation is an analytical study connected to the test's maker.
Salivary cortisol panels for "adrenal fatigue"
Not validated / not recommendedWhat it can tell you
Late-night salivary cortisol is a valid test for Cushing's syndrome — a different use.
What it can't tell you
"Adrenal fatigue," which a 2016 systematic review concluded does not exist as a condition.
Worth knowing: Real adrenal insufficiency is tested with morning blood cortisol or an ACTH stimulation test.
Source: Reference 1
Reverse T3
Not validated / not recommendedWhat it can tell you
Useful in rare situations such as critical illness.
What it can't tell you
Whether you have hypothyroidism. The American Thyroid Association says it doesn't help with that.
Source: Reference 2
Thyroid antibodies (TPO)
Useful in specific situationsWhat it can tell you
Whether Hashimoto's is the cause of an abnormal or borderline thyroid result.
What it can't tell you
Much when repeated over time — the ATA says following antibody levels isn't helpful.
Source: Reference 2
Organic acids test (OAT)
Not validated / not recommendedWhat it can tell you
Valid for diagnosing rare inherited metabolic disorders, usually in infants.
What it can't tell you
"Mitochondrial function," "yeast overgrowth" or nutrient status in adults. Insurers classify these uses as not medically necessary because no evidence supports them.
IgG food sensitivity panels
Not validated / not recommendedWhat it can tell you
Which foods you've been eating — IgG reflects exposure and tolerance.
What it can't tell you
Food allergy or intolerance. Allergy societies in Europe, the US and Canada advise against these tests, and they can lead to unnecessarily restrictive diets.
Source: Reference 3, 4
Hair mineral analysis
Not validated / not recommendedWhat it can tell you
Nothing reliable.
What it can't tell you
Nutrient or toxic metal status. When identical hair samples were sent to six labs, results for 12 minerals differed more than tenfold.
Source: Reference 5
"Provoked" urine heavy metal test (after a chelating drug)
Not validated / not recommendedWhat it can tell you
Nothing reliable — chelating drugs raise metal levels in urine in almost everyone.
What it can't tell you
Whether you have metal poisoning. The American College of Medical Toxicology advises against this test, and chelation itself carries risks.
Source: Reference 6
MTHFR gene test
Not validated / not recommendedWhat it can tell you
Which common gene variants you carry — they're very common in the general population.
What it can't tell you
Your clotting risk or the cause of pregnancy loss. The American College of Medical Genetics says it should not be ordered as part of an evaluation for clotting disorders.
Source: Reference 7
Zonulin ("leaky gut") test
Not validated / not recommendedWhat it can tell you
Nothing reliable.
What it can't tell you
Intestinal permeability. A 2018 study found a widely used commercial kit doesn't detect zonulin at all. See also our gut barrier page.
Source: Reference 8
Intracellular micronutrient panels (e.g., SpectraCell)
Not validated / not recommendedWhat it can tell you
No proven advantage over standard blood tests for specific nutrients.
What it can't tell you
Validated deficiency status. Insurers classify it as investigational.
Continuous glucose monitors without diabetes
Limited evidenceWhat it can tell you
How your blood sugar responds to meals and activity.
What it can't tell you
Whether those responses matter for your health — there's no agreed normal range and no outcome evidence yet.
Full-body MRI and "longevity" panels
Not validated / not recommendedWhat it can tell you
Can find things — often harmless ones that lead to more tests.
What it can't tell you
The American College of Radiology says there isn't enough evidence to recommend total-body screening in people without symptoms.
Source: Reference 9
Lyme tests from non-FDA-cleared labs
Not validated / not recommendedWhat it can tell you
Nothing reliable.
What it can't tell you
The CDC recommends Lyme testing only with FDA-cleared tests using a two-step process.
Source: Reference 10
Why do these tests look so convincing?
Reports often show dozens of results with color-coded "optimal" ranges and a supplement plan attached. But a lab can measure something accurately (that's what certification checks) while the result still doesn't mean what the report says it means (that's what validation would check, and most of these tests never get it).
What should I ask before paying for one?
What sources does this page use?
- Cadegiani FA, Kater CE. Adrenal fatigue does not exist: a systematic review. BMC Endocr Disord. 2016;16:48. doi:10.1186/s12902-016-0128-4
- American Thyroid Association. Thyroid function tests (patient information). https://www.thyroid.org/thyroid-function-tests/
- Carr S, et al. CSACI position statement on the testing of food-specific IgG. Allergy Asthma Clin Immunol. 2012;8:12.
- Stapel SO, et al. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force report. Allergy. 2008;63:793–796.
- Seidel S, et al. Assessment of commercial laboratories performing hair mineral analysis. JAMA. 2001;285(1):67–72.
- American College of Medical Toxicology. Position statement: post-challenge urine metal testing. J Med Toxicol. 2013. doi:10.1007/s13181-013-0350-7
- Hickey SE, et al. ACMG practice guideline: lack of evidence for MTHFR polymorphism testing. Genet Med. 2013;15(2):153–156.
- Scheffler L, et al. Widely used commercial ELISA does not detect precursor of haptoglobin2, but recognizes properdin as a potential second member of the zonulin family. Front Endocrinol. 2018;9:22. doi:10.3389/fendo.2018.00022
- American College of Radiology. ACR statement on whole-body MRI screening. 17 April 2023.
- CDC. Lyme disease: diagnosis and testing. https://www.cdc.gov/lyme/hcp/diagnosis-testing/
How should I cite this page?
Niehaus L. Functional medicine tests: what the evidence actually says. The Lily Perspective. Published October 2026. Updated October 2026. https://lilyperspective.com/toolkit/lab-tests/functional-tests
© 2026 Lily Niehaus. All rights reserved. You're welcome to link to this page or quote short passages with credit to The Lily Perspective.