Functional medicine glossary: care, costs and lab tests

This functional medicine glossary explains 40 terms used in care-model descriptions, practice bills, and lab reports. Use it to translate unfamiliar language and prepare questions for a clinician. It is not a list of tests everyone needs: the reason for a test and the decision it may change matter as much as its name.

Jump to care models, costs, lab tests, or understanding results. If you are reading a lab report, start with reference range and “normal” labs.

Care models

Functional medicine

An approach to chronic illness that asks what may be driving a problem and builds a plan around the person. It is not a medical license or a board specialty, and research on the full model is still limited. Read more in What is functional medicine?.

Root-cause medicine

A way of looking at symptoms that asks why they started, not only how to quiet them. It is not its own medical specialty, and people often use the name for visits that borrow from functional medicine. Read more in What is root-cause medicine?.

Concierge medicine

A practice model in which you pay a membership or retainer fee for closer access to a doctor, such as longer visits and direct contact. Medicare does not pay that fee. Read more in What is concierge medicine?.

Direct primary care

A model in which you pay a flat periodic fee, usually monthly, for a defined set of primary care services instead of billing insurance for those visits. Most people still keep separate insurance for hospitals, specialists and emergencies. Read more in What is direct primary care?.

Membership medicine

An everyday name for practices that charge a recurring fee for access and a set of services, including concierge and direct primary care practices. What the fee covers varies by practice, so read the contract.

Family medicine

The medical specialty that cares for people of every age over many years, often as the first contact for a new health worry. Read more in What is family medicine?.

Cash-pay practice

A practice that charges patients directly for care rather than billing an insurer for those services. Ask whether you can request an itemized receipt and whether your insurance offers any reimbursement.

Telehealth

Care provided remotely using communication technology rather than in the same exam room. The appropriate format depends on the service; a hands-on exam or blood draw may still need an in-person visit. Our Texas telehealth guide explains one state’s rules.

Nurse practitioner

A registered nurse with advanced education and training who can assess and treat health conditions within their licensed scope. MedlinePlus explains that state rules affect the role, including prescribing and work with physicians.

Collaborative or delegating physician

A physician who works with another clinician under an arrangement required for particular tasks by state law. In ordinary Texas outpatient practice, prescribing can be delegated to a nurse practitioner through a prescriptive authority agreement; other settings have separate provisions.

Prescriptive authority agreement

A written agreement used for physician delegation of prescribing in Texas outpatient practice under section 157.0512. It identifies permitted prescribing and plans for consultation, referral, emergencies, and documented meetings at least monthly.

Board certification

A specialty credential separate from the state license that permits medical practice. For physicians, check the certifying board and the exact specialty rather than relying on the phrase alone; ABMS lists its recognized specialties.

Cost

Membership fee

A recurring payment to a practice for the services and access defined in its contract. It is not health insurance, and you should check what is excluded as well as what is included.

HSA

A health savings account: a tax-advantaged account for qualified medical expenses, with eligibility rules for making contributions. IRS Notice 2026-05 allows certain DPC arrangements beginning in 2026, but contribution eligibility and reimbursement are separate questions. See the DPC guide before assuming a membership qualifies.

FSA

A flexible spending account, usually offered through an employer, that uses tax-advantaged funds for eligible healthcare expenses. Its rules differ from an HSA, so ask the plan administrator whether a specific practice fee qualifies.

Superbill

An itemized receipt from a practice that lists the services, the diagnosis and billing codes, and what you paid. Some insurance plans let you send it to request out-of-network reimbursement. Whether you're paid back, and how much, depends on your plan.

In-network

A clinician or practice with a contract with your insurance plan to give care at set rates.

Out-of-network

A clinician or practice without a contract with your insurance plan. Plans often pay less, or nothing, for out-of-network care, so you may pay more yourself.

Deductible

The amount you pay for covered services before your insurance begins paying under its terms. Some services can be covered before you meet it, so check your plan’s rules; HealthCare.gov explains the distinction.

Coinsurance

Your share of the cost of a covered service, as a percentage, after you've paid your deductible. Plans often set a higher share for out-of-network care.

Lab tests

Lipid panel

A blood test for cholesterol and triglycerides that usually reports LDL cholesterol, HDL cholesterol, total cholesterol, and triglycerides. It is also called a cholesterol test or lipid profile.

LDL

Low-density lipoprotein, often called bad cholesterol. It is the main source of the buildup that can block arteries.

HDL

High-density lipoprotein, often called good cholesterol. It helps carry cholesterol away from the arteries.

Triglycerides

A type of fat in the blood that your body uses for energy. A lipid panel measures it along with cholesterol.

ApoB

Apolipoprotein B, a protein involved in carrying fats such as cholesterol in the blood. An ApoB blood test measures this protein, which is a different measurement from the amount of LDL cholesterol.

Fasting insulin

A test of insulin in the blood after a specified period without food. MedlinePlus explains that insulin results are interpreted alongside blood glucose and other information; the number is not a diagnosis by itself.

HbA1c

Hemoglobin A1C, a blood test that reflects average blood sugar over roughly the past two to three months. It can help screen for or monitor diabetes, with interpretation based on the clinical situation.

Comprehensive metabolic panel

A blood test that measures 14 substances, including glucose, calcium, electrolytes, and kidney and liver measures. It is often shortened to CMP.

TSH

Thyroid-stimulating hormone, made by the pituitary gland to tell the thyroid how much hormone to make. It is usually the first thyroid test a clinician orders.

Free T4

The amount of thyroxine, the main hormone the thyroid makes, that is not bound to proteins in the blood. It is often checked with TSH.

Free T3

The unbound form of triiodothyronine, a thyroid hormone. The American Thyroid Association notes that free T3 measurements are often not reliable and are not usually helpful.

Reverse T3

An inactive form of T3. The American Thyroid Association says reverse T3 does not help determine whether hypothyroidism is present in healthy people who are not hospitalized.

Thyroid antibodies

Blood tests for antibodies that attack the thyroid, most often thyroid peroxidase and thyroglobulin antibodies. They can help find an autoimmune cause of a thyroid problem, such as Hashimoto's thyroiditis.

Ferritin

A protein that stores iron; a ferritin blood test helps assess iron stores. Inflammation and other conditions can raise it, so a high result does not automatically mean too much stored iron.

Vitamin D

The usual vitamin D blood test measures 25-hydroxyvitamin D to assess vitamin D status. A different test of active vitamin D is used for particular kidney or calcium questions.

hs-CRP

High-sensitivity C-reactive protein, a test that detects small increases in a protein associated with inflammation. MedlinePlus distinguishes this test, used to help assess heart-disease risk, from the standard CRP test.

Sex hormone panel

A set of blood tests of hormones such as estrogen, progesterone, testosterone and FSH. Which tests are included, and when in the cycle they are drawn, depends on why your clinician orders them.

Understanding results

Reference range

The range of values a laboratory uses for comparison, usually based on results from a group of healthy people. MedlinePlus explains that ranges differ between labs and that a result outside the range may or may not indicate a problem.

Optimal range

A target described as preferable to a lab’s reference range. The term alone does not identify a shared standard or a guideline, so ask which evidence supports the target and whether reaching it changes a health outcome.

"Normal" labs

Results that fall within the laboratory’s reference ranges. MedlinePlus cautions that a normal result does not rule out every health problem and an abnormal result does not always mean disease; symptoms and history help determine the next step.

How should you use this functional medicine glossary?

Bring the unfamiliar term and the actual report or quote to the visit. For a lab result, include the units and that lab’s reference range rather than comparing the number with a range found elsewhere. Ask: “What question does this answer, what remains uncertain, and what would we do differently because of it?”

For a care model or fee, ask for the written service list. For a credential, ask which organization grants it and what licensed role the person holds. These small checks turn a definition into a more useful conversation.