Subscribe to the Magazine for free
Subscribe for free to keep reading! If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.

How Functional Medicine Providers Look at "Optimal" Lab Values

Medically reviewed by 
How Functional Medicine Providers Look at "Optimal" Lab Values

Picture this. You feel unwell, you can’t quite pinpoint why, but you know something is just not right. Maybe its hormones or possible mineral or vitamin deficiency. Whatever it is, you just can’t shake the feeling that something is off. You go see your primary care and they run the standard labs. The doctor comes in and says, “all of your lab results are normal.”

How can this be? Your body is telling you something is wrong and yet standard lab reference ranges say you are “normal”.

This is where Functional Medicine shines in my opinion. Functional Medicine Practitioners don’t always focus on standard lab ranges. They more commonly use “optimal” lab values, which can show dysfunctions in the body at the cellular level, years before a patient is diagnosed with a disease.

In this article, we are going to compare some optimal ranges vs standard lab ranges on four commonly ordered functional medicine tests. But before we begin, we should really narrow down the difference between the allopathic standard lab values versus functional medicine “optimal” lab values.  

Standard Lab Ranges

Standard lab reference ranges are broad reference ranges used by the laboratories that analyze samples based on averages of a healthy population. These test help doctors make diagnoses and treatment decisions based on high or low values, but they don’t always tell you what’s optimal.

Lab test results can fall within the normal reference range in the early stages of the disease due to such a wide reference range on standard lab tests. This can lead to cellular dysfunctions in the body being overlooked.

Functional Medicine Optimal Range

Functional Medicine lab ranges are usually much narrower than standard lab ranges. They are labeled “optimal lab values,” meaning anything outside of those optimal values can show patterns and markers that spot trends toward disease. By catching these markers early on, functional medicine practitioners have a chance at reversing or stopping disease progression altogether.  

Below is a comparison on four commonly ordered lab tests and the difference between how functional medicine practitioners look at them vs allopathic standard reference ranges.


Most doctors will only test for TSH when accessing thyroid function. While TSH is an excellent thyroid marker, it only points to general dysfunction of the thyroid. Without the rest of the thyroid markers, it provides very little value of where the actual dysfunction is coming from.

A Full thyroid evaluation should include:

  • TSH
  • Total and free T3 and T4
  • T3 Uptake
  • Reverse T3

Reference Range for TSH

Standard Reference Range: 0.45-4.12 mlU/L

Functional Medicine Optimal Range: TSH of 0.5-2.5 mlU/L

Reference Range for T3

Standard Reference Range: 2.8-4.0 mlU/L

Functional Medicine Optimal Range: 2.8-4.0 mlU/L

Reference Range for T4

Standard Reference Range: 0.93-1.70 mlU/L

Functional Medicine Optimal Range: 0.93-1.70 mlU/L

Reference Range for Reverse T3

Standard Reference Range: 8-25 ng/dl

Functional Medicine Optimal Range: Less than 15 ng/dl

Top Functional Medicine Complete Thyroid Panels Ordered Through Rupa Health

Boston Heart Diagnostics
Doctors Data

Vitamin D

Vitamin D comes from three main sources: sun exposure, diet, and supplements.

Even with adequate sun exposure and a varied diet, vitamin D deficiency is prevalent and affects over 40% of people in North America.

Vitamin D Deficiency is directly linked to several health concerns, including osteoporosis, heart disease, cancer, and impaired immune function. Functional Medicine practitioners like to see Vitamin D levels slightly higher than allopathic doctors. Research shows that higher levels of vitamin D help decrease inflammation and is associated with less risk of disease.

Testing for Vitamin D is quite simple, and most labs offer a blood spot option that patients can do from the comfort of their own homes.

Reference Range for Vitamin D

Standard Reference Range: 20 and 40 ng/mL

Functional Medicine Optimal Range: 40-70 ng/mL

Top 3 Functional Medicine Vitamin D Test Ordered Through Rupa Health

US BioTek
Great Plains Laboratory


Insulin resistance currently affects 1 in 3 Americans and is a precursor to prediabetes and eventually type 2 diabetes if not managed through nutrition and lifestyle intervention.

There is no one lab test that can directly screen for insulin resistance but looking at the entire clinical picture alongside labs can show abnormalities in cellular glucose metabolism long before one actually develops diabetes. Therefore, we owe it to our patients to screen for evidence of glucose dysregulation as early as possible.

Insulin resistance (IR) marks the beginning of these metabolic changes and can be detected via blood work, glucose tolerance tests, or continuous glucose monitors.

Reference Range for Hgba1c

Hgba1c is a blood test that measures your average blood sugar levels over the past three months using a percentage point.

Standard Reference Range: Under 5.7

Functional Medicine Optimal Range: 4.6-5.5

Reference Range for Fasting Insulin

Insulin resistance is characterized by increased insulin levels in the blood.

Standard Reference Range: 2.6-24.9 mcIU/ml

Functional Medicine Optimal Range: 4.6 – 5.5 mcIU/ml

Reference Range for Fasting Glucose

This is a measure of how much glucose (sugar) is in your blood after an overnight fast.

Standard Reference Range: 70 – 125 mg/dL

Functional Medicine Optimal Range: 70- 85 mg/dL

Top 3 Functional Medicine Insulin Resistance Test Ordered Through Rupa Health

Access Medical Laboratories


Cortisol follows a circadian rhythm starting with the cortisol awakening response (CAR) upon waking. Cortisol should be highest in the morning and lowest during the evening.  But cortisol can rise and be out of balance during the day due to stress, chronic pain, and blood sugar dysregulation.

Long therm high cortisol levels throughout the day can cause weight gain, sleep disturbances, temperature fluctuations, and chronic fatigue.

Most traditional doctors will test cortisol in the am, only getting a direct read on morning cortisol levels. But this does the patient no good if their cortisol levels are fluctuating throughout the day.

Functional medicine providers will normally test cortisol throughout the day with four different salivary samples. This type of testing gives insight into the natural circadian daily cortisol rhythm and help clinicians address the time that specific daily stressors are occurring.

Reference Range for Cortisol

8am to 12pm:  5-25 mcg/dL

Functional medicine optimal ranges can change based on the specialty lab used. Each lab test will guide you through the exact time slots to measure. These tests are usually done via salivary testing and can be done at the patient’s home.

Two important things to keep in mind for cortisol awakening response are:

  • Cortisol should be highest 30 mins after waking and should continue to drop throughout the day. There should be no peaks throughout the day.
  • Use a test that allows multiple samples throughout the day, including morning, midday, afternoon, and evening.

Top 3 Functional Medicine Cortisol Awakening Response Test Ordered Through Rupa Health

Genova Diagnostics
Doctor's Data/Labrix


Most standard lab reference ranges are very wide allowing disease progression to possibly go undetected. Functional medicine optimal ranges are usually much narrower, allowing practitioners to foresee possible dysfunction so they may intervene early with nutrition, supplements, and lifestyle adjustments to help patients prevent disease.

Similar Articles You May Be Interested in:

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
Learn More
No items found.

Lab Tests in This Article

Subscribe to the Magazine for free to keep reading!
Subscribe for free to keep reading, If you are already subscribed, enter your email address to log back in.
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
Are you a healthcare practitioner?
Thanks for subscribing!
Oops! Something went wrong while submitting the form.
See All Magazine Articles