Five Lab Tests Your Doctor Isn’t Ordering

March 17th, 2023

By Kelly Brogan, M.D.

Guest Writer for Wake Up World

Have you been diagnosed with an ‘incurable’ disease like depression? Were you told that your only hope is to manage your symptoms by taking lifelong medications? What if you could eliminate this diagnosis by simply fixing nutrient deficiencies or correcting physiologic imbalances? As such, proper blood tests can highlight these vulnerabilities and guide healing protocols.

Some recommend running as many tests as possible, which can get expensive and confusing. Years of clinical practice and a deeper understanding of common symptoms have led me away from running dozens of lab tests. For example, I no longer order salivary cortisol testing, as the results confirm what we already know: we’re enduring unprecedented levels of stress. I’m happy to share with you the five most common and helpful blood tests that I still use with my patients.

1. Thyroid function tests

These tests show how well your thyroid gland is working. As the thyroid is the master regulator of metabolism, people with weight problems, depression, brain fog, anxiety, and constipation often have impaired thyroid function. Thyroid function tests give information about how well your brain is sensing hormone levels. Furthermore, these tests show how your immune system is interacting with your thyroid.

I’ll skip the complexities of thyroid hormone production and regulation, which are covered comprehensively in this article. The key takeaway is that your brain and thyroid gland produce hormones called Thyroid Stimulating Hormone (TSH), T3, and T4. T3 is the active form of thyroid hormone, and it can exist as either free T3 (FT3) or reverse T3 (RT3).

To screen for problems, most conventional doctors test only for TSH and possibly T4. However, as T3 is one of the body’s master molecules, it’s important to know free (unbound) T3 levels. For example, T3 helps regulate digestion, energy use, and hormonal balance.

An autoimmune disease called Hashimoto’s thyroiditis is the most common cause of hypothyroidism in women. I am living proofthat this type of thyroid autoimmunity can be reversed, even if you’ve been on a synthetic replacement (like Synthroid) for years. Dessicated thyroid replacement, a natural form of thyroid hormone, can sometimes be the first step to feeling better. Importantly, lifestyle factors, especially nutrition, are essential for long-term optimal health and true, lasting healing.

To screen for thyroid autoimmunity, I order a panel to measure thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb).

Years of clinical practice and learning from experts have taught me the optimal values for thyroid health, which I’ll share with you now:

Optimal values:

  • TSH: less than 2 ?U/mL
  • Free T4: ideally over 1.1 ng/dL
  • Free T3 (FT3): ideally over 3.0 pg/mL
  • Reverse T3 (RT3): less than a 10:1 ratio RT3:FT3
  • TPOAb: less than 4 IU/mL (or negative according to lab range)
  • TgAb: less than 4 IU/mL (or negative according to lab range)

2. Vitamin B12

Adequate levels of Vitamin B12 are critical for brain health. Yet almost 40% of Americans are deficient in Vitamin B12. Gut dysbiosis, poor digestion (often from hypothyroidism!), eating inflammatory foods, and using certain medications can cause B12 deficiency. Specifically, heartburn medication, which suppresses stomach acid, blocks the absorption of Vitamin B12.

Vitamin B12 is an all-star antidepressant that is essential to make red blood cells, line nerve cells, and keep our brains functioning properly. Vitamin B12 deficiency has been linked to deep depression, paranoia, and memory loss, among other serious conditions. Furthermore, pregnant women deficient in B12 may put their babies at risk for neurological disorders, developmental delays, and cognitive and motor impairments.

While deficiency is usually defined as having blood levels below 200 pg/mL, I like to see patients above 600 pg/mL. Importantly, blood tests for B12 don’t tell the whole story; this vitamin works inside cells, and blood levels won’t tell you your brain levels of B12. Therefore, it’s helpful to complement this test by measuring homocysteine.

Homocysteine is an inflammatory protein that is metabolized by Vitamin B12 and folate. When someone has high blood levels of homocysteine, it indicates that Vitamin B12 is low. This surrogate marker provides more information on how well your brain and body are functioning.

The optimal level of homocysteine is between 7 – 10 ?Mole/L, but when I see a homocysteine level over 8, I recommend supplementing with B12 to quench inflammation.

3. High-sensitivity C-Reactive Protein (hs-CRP)

C-reactive protein (CRP) is another general marker of inflammation, and you want to have blood levels of CRP under 1.0 mg/L. Numerous studies, including meta-analyses that have analyzed tens of thousands of people, show that elevated CRP is associated with depression and anxiety (1-3).

4. Fasting glucose/insulin/Hemoglobin A1C

These tests check blood sugar control. The most telling of these tests is Hemoglobin A1C, as it gives an average of your blood sugar levels over the past 90 days. The fasting glucose test provides a snapshot of how much sugar is present when your body isn’t processing food. The fasting insulin test gives insight on how your pancreas is functioning while you’re not eating.

Unstable blood sugar can masquerade as anything from fatigue to panic attacks to ADHD. These symptoms reveal that the body is overloaded and struggling to “put away” ingested sugars. Therefore, understanding your blood sugar control can help identify the root causes of several physiologic symptoms. Making dietary and lifestyle changes to combat the blood sugar roller coaster can heal a startling number of diseases. Amazingly, according to some field research, even diabetes can be reversed in a little over a month (4)!

These findings can help you heal your relationship to starches and natural sugars and to understand their health properties relative to processed forms.

Optimal values:

  • Hemoglobin A1C: 4.8 – 5.2%
  • Fasting glucose: 70 – 85 mg/dL
  • Fasting insulin: below 6 ?IU/mL

5. Vitamin D

Most Americans are deficient in this critical hormone-vitamin (5). Vitamin D is important for proper nutrient absorption, cognition, and immune function (6). Lack of sun exposure and high food levels of pesticides can lead to Vitamin D deficiency.

I test my patients for Vitamin D – called 25(OH)D clinically – as well as its activated form (called 1,25). The optimal levels for 25(OH)D are between 50 – 80 ng/mL, coupled with an assessment of 1,25 to determine whether it is above the normal reference range.

Recent interesting work has called these recommended ranges into question. Dr. Chris Masterjohn shows that optimal Vitamin D levels may depend on ethnicity and nutrient status (7). For example, non-Caucasians have lower levels of 25(OH)D than Caucasians, but they have no adverse effects (8). Additionally, hunter-gatherer populations have 25(OH)D levels that would be considered deficient, though they enjoy plenty of sun exposure and healthy lives (9).

Therefore, I’ve found that measuring other biological markers is helpful to determine how Vitamin D is being used in the body. Testing for parathyroid hormone (PTH) and calcium, along with 25(OH)D, gives a more accurate picture of Vitamin D metabolism. Read this article for a more detailed explanation of the mechanisms.

Overall, it’s important to know how Vitamin D is working in your body before taking supplements, as excess Vitamin D supplementation can be harmful (10). To optimize Vitamin D levels, I recommend getting outside and eating nutrient-rich foods. Foods such as organ meats and oily fish contain healthy fats and micronutrients, including magnesium, that combat Vitamin D toxicity.

What if your doctor won’t order these tests?

You can choose to engage a comprehensive healing effort to see whether your symptoms can completely resolve within one to two months before pursuing these diagnostics.

But if you have worked through a program and are still stuck, these blood tests are a great way to begin to learn more about your physiology. Some doctors are hesitant to order these tests. They may tell you that they’re unnecessary. A naturopath or functional medicine doctor is more likely to understand these tests and order them for you.

If you feel that you have unresolved symptoms, you must advocate for yourself and demand this baseline assessment. Many of these tests are covered by insurance or are not terribly expensive. Don’t be afraid to push back if your doctor is dismissive. The moments of awkwardness are worth understanding what’s happening in your body. You may need to go elsewhere for these blood tests – or even order them on your own. Information revealed in these tests will help identify the best support for your healing.



Originally published at and reproduced here with permission.

About the author:

Kelly Brogan, M.D. is a holistic women’s health psychiatrist, author of the NY Times Bestselling book, A Mind of Your Own, the children’s book A Time For Rain, and co-editor of the landmark textbook, Integrative Therapies for Depression. She completed her psychiatric training and fellowship at NYU Medical Center after graduating from Cornell University Medical College, and has a B.S. from M.I.T. in Systems Neuroscience. She is board certified in psychiatry, psychosomatic medicine, and integrative holistic medicine, and is specialized in a root-cause resolution approach to psychiatric syndromes and symptoms. She is on the board of GreenMedInfo, Price-Pottenger Nutrition Foundation, Functional Medicine University, Pathways to Family Wellness, Mindd Foundation, SXSW Wellness, Chickasaw Nation Wellness, and the peer-reviewed, indexed journal Alternative Therapies in Health and Medicine. She is Medical Director for Fearless Parent and a founding member of Health Freedom Action. She is a certified KRI Kundalini Yoga teacher and a mother of two. For more articles, sign up for her newsletter at

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