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Uncovering the Root Causes of Fatigue: Essential Blood Tests for Your Health

Updated: 35 minutes ago

If you’re constantly exhausted, struggling to focus, or relying on caffeine to get through the day, the right blood work can reveal why. Feeling tired all the time is one of the most common reasons people seek lab testing. Fatigue can stem from many different causes—anything from nutrient deficiencies to thyroid changes to chronic infections. Getting the right blood work is the first step to finding out why your energy is low.


Understanding Fatigue: Why It Happens


Fatigue isn't just about feeling sleepy. It can affect your mood, concentration, and overall quality of life. Understanding the underlying causes is crucial. Here are some common reasons:


  • Nutrient Deficiencies: Low levels of essential vitamins and minerals can lead to fatigue.

  • Thyroid Issues: An underactive thyroid can slow down your metabolism, causing tiredness.

  • Chronic Infections: Conditions like Lyme disease or viral infections can sap your energy.


Quick Answer: Key Labs for Fatigue


The most important labs for fatigue usually include:

  • Complete Blood Count (CBC)

  • Comprehensive Metabolic Panel (CMP)

  • Full Thyroid Panel

  • Iron Studies including Ferritin

  • Vitamin B12

  • Vitamin D

  • Sometimes additional hormone or inflammation markers.


In our practice, we often see people who have had only basic labs run, such as a CBC and a CMP, maybe a TSH, but not much more. Digging deeper into thyroid, iron, or vitamin D often uncovers answers regular screening misses.

What Labs Should I Order or Ask For?


Complete Blood Count (CBC)


This test checks for anemia, infections, and overall blood health. Low red blood cells or hemoglobin could indicate possible anemia. High white blood cells might suggest infection or inflammation.


Comprehensive Metabolic Panel (CMP)


This panel looks at liver and kidney function, blood sugar, and electrolytes. Abnormal glucose levels could indicate blood sugar issues such as diabetes or hypoglycemia. High or low liver/kidney markers might suggest sluggish detox or filtration.


Thyroid Panel


A TSH test alone isn’t enough. Ask for TSH (thyroid-stimulating hormone), Free T4, Free T3, and thyroid antibodies (TPO, TgAb) if autoimmune thyroid disease is suspected.


Many of our patients had only TSH checked, which misses subclinical hypothyroidism or autoimmune thyroid patterns. If their hypothyroidism is due to an autoimmune condition, they need to know! Their risk for additional autoimmune disease is much higher, and we can start a protocol to help prevent that, but only if we know.

Iron Studies


Iron deficiency is a leading cause of fatigue. Ferritin (iron storage), serum iron, total iron-binding capacity (TIBC), and transferrin saturation are typically included in an "iron panel."


Vitamin B12 and Folate


Low levels can lead to fatigue, brain fog, and mood changes.


Vitamin D (25-hydroxy)


Deficiency is linked with fatigue, low mood, and poor immune function. Levels below 30 ng/mL indicate deficiency, while levels between 30–50 are often considered suboptimal for energy. The optimal range for most people is 50–80 ng/mL.


Other Helpful Markers (Depending on History)


  • Cortisol: Assess adrenal function with four saliva samples throughout the day.

  • Sex Hormones: Estradiol, progesterone, testosterone, and DHEA can be particularly helpful in perimenopause/andropause.

  • Inflammation Labs: Chronic low-grade inflammation can drive fatigue.

  • Viral Studies: If fatigue started after an illness, common viral causes like COVID-19 or Epstein-Barr Virus may need treatment.


Lab test supplies

When Should I Consider Functional Labs?


If Basic Labs Don’t Give Answers


Deeper testing may help:

  • Comprehensive Stool Analysis: Assesses gut health, digestion, microbiome, and malabsorption.

  • Adrenal Stress Profile: Evaluates stress, cortisol patterns, and the need for coffee to get through the day.

  • Food Sensitivity Testing: Identifies hidden triggers that drain energy and cause inflammation.

  • Environmental Toxin Testing: This includes mycotoxins from mold and fungi. It’s especially helpful if there’s a history of living in a home with water damage or exposure to chemicals.


We often add functional labs if standard workups don’t explain ongoing fatigue. These can finally uncover patterns that routine blood work has missed and get patients on a path to feeling better.

How Do I Order These Tests?


Functional Labs page allow you to order many of these without a doctor’s visit.


Wellness & Nutrition Panel
Buy Now

Tip: Always review your labs with a qualified practitioner to understand what the results mean for you.


How direct order Functional Lab Testing works.

Takeaway


If you’re tired all the time, the right labs can help uncover the root cause. Start with a broad panel—CBC, CMP, thyroid, iron, B12, vitamin D—and layer on more targeted tests if needed.


Living with fatigue is no way to live, and it isn't normal. Don't try to manage it with medications, coffee, and stimulants—long-term, these are not sustainable.

Finding Solutions


We can find the answers with the right assessment and testing. When you have the information, you can make better decisions on a treatment path to address the root causes.


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References


Frequently Asked Questions (FAQ)


  1. What blood tests are most important if I always feel tired?

    The most common starting labs include a Complete Blood Count (CBC), Comprehensive Metabolic Panel (CMP), thyroid panel (TSH, Free T4, Free T3), iron studies (including ferritin), vitamin B12, and vitamin D. Depending on your history, hormone or inflammation markers may also be helpful.


  2. Can vitamin D deficiency make me tired?

    Yes. Low vitamin D levels are linked to fatigue, low mood, and weak immunity. Many people feel more energy once their vitamin D level is brought into the optimal range.


  3. How do thyroid problems cause fatigue?

    The thyroid gland regulates metabolism. If thyroid hormone is too low (hypothyroidism), it slows down energy production, causing fatigue, brain fog, weight gain, and low mood. A full thyroid panel is needed—not just TSH—to see the full picture.


  4. Should I test for iron if I’m tired?

    Yes. Iron deficiency anemia is one of the most common causes of fatigue, especially in women. Checking ferritin, serum iron, and TIBC can show if low iron is affecting your energy.


  5. Do I need a doctor to order these labs?

    Not always. Many tests can be ordered directly through direct-to-consumer lab services such as our website. However, it’s important to review results with a qualified practitioner to understand what they mean for your individual health.


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