Functional lab testing extends beyond conventional tests to assess body systems such as gut function, hormone balance, nutrient absorption and detoxification. By analyzing a broader range of biomarkers and using wider reference ranges, practitioners can design personalized nutrition, lifestyle and supplement strategies that address the underlying drivers of health.

When applied judiciously, functional testing empowers patients with actionable insights, guiding them toward improved digestion, nutrient utilization, hormonal balance and overall well-being. Dr. Aumatma Simmons, a double board-certified naturopathic doctor and endocrinologist, underscores the importance of collaborating with a professional before undertaking functional lab testing to save time, money and confusion. Not all tests are equally reliable, and an experienced practitioner can help separate the fluff from the facts.

“I do not like to over-test because of the expense. If an elimination diet brings symptom relief, for example, then less testing and fewer supplements are needed,” states Lorraine Maita, M.D., an internal, integrative and functional medicine specialist at The Feel Good Institute.

 

Limits of Conventional Lab Work

 

“Conventional lab testing is designed based on averages, and those averages are not always what’s optimal,” explains Simmons, noting that many conventional reference ranges are broad, encompassing a diverse population without specifying what truly constitutes ideal health. From a functional perspective, she says, lab tests are interpreted with a focus on optimizing health, rather than merely adhering to the normal range.

According to Maita, another limitation of conventional lab tests is that they solely indicate the presence of nutrients in the bloodstream without providing insight into the body’s actual absorption or utilization of those nutrients. “Just because you’re eating healthy does not mean that food is being digested, absorbed and assimilated. A lot of blocks can happen along the way,” she explains, adding that functional lab testing adds more detail to help clarify what is really going on in the body.

 

Common Functional Testing

 

Stool Test for Gut and Immune Function: A stool test examines the presence and absence of microorganisms to gain a better understanding of the gut microbiome within the body. In addition to taking a census of the various beneficial bacteria, this test also assesses the presence or absence of specific digestive enzymes, parasites, worms, yeast or inflammation markers. In Maita’s practice, this test allows her team to provide personalized, precision medical care to address microbiome imbalances and immunological stressors.

 

Food Sensitivity Testing: These tests are designed to assess the immune system’s reaction to specific foods or food additives. The Mediator Release Test (MRT), used by Simmons, “looks at all of the specific white blood cells in the body and how they respond to a specific food,” she explains. Unlike allergy tests that detect immediate reactions, the MRT identifies delayed immune responses that may cause bloating, fatigue, headaches, joint pain, skin issues or other chronic symptoms. According to Simmons, the results guide personalized dietary modifications to reduce inflammation and enhance overall wellness.

Maita notes, “Food sensitivity testing is sometimes helpful for people who can’t tell what their trigger foods are by just doing an elimination diet. I like to use the Vibrant Wellness test. It will show them if they’ve made antibodies to food, which suggests how well they might do when they remove those foods.”

 

Functional Nutrient Test: While conventional testing measures the presence of nutrients in the bloodstream, an intracellular blood test—also known as micronutrient testing or functional nutrient testing—measures nutrient levels within red and white blood cells, thus determining whether nutrients are being properly absorbed and utilized by the body.

“A lot of people are taking supplements, but their GI [gastrointestinal system] isn’t absorbing any of it,” Simmons points out, highlighting how functional testing can uncover hidden inefficiencies that standard blood tests and supplementation alone might miss. Citing the trending supplement CoQ10 as an example, she notes that a functional nutrient test may suggest that a patient should take a different form of the supplement for better absorption.

 

Dried Urine Test for Comprehensive Hormones (DUTCH): This test provides a comprehensive analysis of adrenal and sex hormone function. Unlike conventional cortisol tests, the DUTCH measures levels four times throughout the day and evaluates cortisol metabolites to explain how the body produces, converts and eliminates cortisol each day.

The DUTCH is also invaluable as a way of mapping the body’s ability to process estrogen. “This is critical because symptoms often attributed to estrogen dominance—such as breast tenderness, irritability, premenstrual syndrome and sub-fertility—are frequently caused, not by excess estrogen itself, but by metabolite buildup or impaired clearance pathways, in which case specialized diindolylmethane (DIM) supplements would be prescribed to support estrogen metabolism,” Simmons explains. “This illustrates why the professional interpretation of DUTCH testing is essential: because it shows whether a hormone imbalance is truly about excess, impaired metabolism or faulty elimination, allowing interventions to be tailored accurately, rather than relying on generalized supplement advice.”

 

Hannah Tytus is an integrative health coach, former writer at the National Institutes of Health and host of the Root Shock podcast, exploring our understanding of health.

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