Functional medicine labs: which tests are worth it?

There is no official list. When people talk about functional medicine labs or functional medicine lab testing, they usually mean two things together: the standard blood work any doctor might order at a checkup, and specialty panels from private labs, often sold directly to patients.

The standard tests are standardized, with known reference ranges and guidelines on when to order them. Specialty panels vary widely: some measure real things with poorly validated methods, and some promise answers science cannot give yet. For the approach itself, read what functional medicine is.

These panels are common in functional medicine clinics and in mail-order kits. A test that measures something is not the same as a result that should change a decision about your health.

• IgG food-sensitivity panels. The AAAAI (American Academy of Allergy, Asthma & Immunology) says the test has never been scientifically proven to do what it reports, and that IgG to a food is likely the immune system's normal response to eating it. It is not valid for diagnosing food allergy or intolerance, and it can lead people to cut foods for no reason.
• Comprehensive stool microbiome panels. An international expert consensus published in 2024 in The Lancet Gastroenterology & Hepatology warned that direct-to-consumer microbiome tests have no proven value in clinical practice.
• Hair mineral analysis. In a study published in JAMA in 2001, one hair sample split between six commercial labs produced results that differed more than tenfold for several minerals, with conflicting reference ranges.
• Salivary cortisol for "adrenal fatigue." The Endocrine Society says there is no scientific proof that adrenal fatigue is a true medical condition, and no test can detect it. Real adrenal disorders exist and are tested differently.
• Urine heavy-metal tests after a "provoking" agent. The American College of Medical Toxicology concluded that measuring urine metals after a chelating agent is not validated, has no demonstrated benefit and may be harmful, because the drug itself raises urine metal levels.
• Organic acids panels. Urine organic acid analysis is a real tool for diagnosing rare inherited metabolic disorders (MedlinePlus). Selling it as a general map of your metabolism or gut is a different claim, and it is not among the screening tests the USPSTF recommends.

A lab's reference range is based on results from large groups of healthy people (MedlinePlus). Many specialty-panel reports add a narrower "optimal" range, so more results get flagged. That "optimal" range is the vendor's own cut-off; ask what study it comes from.

MedlinePlus notes that it is common for healthy people to have a result outside the reference range. The more tests you run, the more likely one gets flagged by chance alone. That result can lead to repeat tests, more expensive workups and worry without a clear benefit. The Choosing Wisely campaign suggests asking, before any test, how likely an inaccurate result is and whether it could lead to more testing.

Many specialty panels are out-of-pocket: health plans usually cover tests a doctor orders for a clinical reason, and many do not cover tests without evidence behind them. Before you pay, ask for the total price in writing, and ask whether it includes the sample collection, shipping and a review of the results with a licensed clinician.

If you are in Puerto Rico, you can book an online visit. Visits are only for people who are physically in Puerto Rico during the visit. The doctor evaluates you and, when clinically appropriate, gives you a lab order for a lab near you. You see Dr. Diana Nieves Castro, a Puerto Rico–licensed general practice physician. When your results come back, read how to read lab results.

We also run an in-person medical and wellness retreat in Puerto Rico. At the retreat, labs are part of the medical care when clinically appropriate: the physician decides which tests, if any, make sense for you, as part of a root-cause approach led by a licensed physician. We do not promise specific tests or results.

To compare retreats, read what to ask any retreat about its medical care, and see what to expect at a retreat.