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The bloodwork panel that actually explains your fatigue
6 min read
Key takeaways
- Most fatigue workups stop at TSH and CBC. That catches thyroid disease and anemia. It misses nine other common causes.
- Ferritin, free testosterone, cortisol AM, fasting insulin, homocysteine, and free T3 are each independently associated with fatigue and are each routinely skipped on a standard panel.
- A comprehensive panel runs all of them in a single blood draw and returns results with clinical reference ranges within 48 to 72 hours.
- The goal is not to find one marker that explains everything. Usually, two or three are running suboptimal at the same time, each contributing a partial load.
The doctor said everything looks normal. The exhaustion did not get the memo
“Everything came back normal.” This is said to exhaust midlife adults every day. It is usually true. The standard panel is normal. It is also incomplete. TSH at 3.1 mIU/L is technically within range and also in the range where a significant percentage of people feel hypothyroid. Ferritin at 18 ng/mL passes the reference range minimum of 12 and still represents iron-deficient cellular function in most tissues.
The standard annual physical runs a CBC, a metabolic panel, and a TSH. That is designed to catch acute pathology. It is not designed to diagnose the low-grade dysfunction that produces the persistent fatigue most midlife adults describe. Two different tools for two different problems.
A Function Health comprehensive panel measures over 100 biomarkers, including those listed below. At $499 per year for two full draws, that is less than the cost of a single specialist appointment in most US cities, no referral required.
The markers that explain most unexplained fatigue
Ferritin. Not just serum iron. Ferritin below 30 ng/mL is associated with fatigue, cognitive fog, and exercise intolerance even without frank anemia. The standard lab range bottoms out at 12 to 15 ng/mL. Optimal for function is 50 to 100 ng/mL for most adults. A ferritin of 22 with normal hemoglobin reads as fine on a standard report. It is not fine. Thorne Iron Bisglycinate is the form with the lowest gastrointestinal side effects and the best absorption profile.
Free testosterone. Total testosterone is easy to find in range while free testosterone (the biologically active fraction) runs low, particularly in men with elevated sex hormone-binding globulin (SHBG). A total testosterone of 480 ng/dL with SHBG of 65 nmol/L leaves very little testosterone available for the brain and muscle to actually use. That is a fatigue cause invisible without the full panel. Hone Health runs the testosterone-focused hormone workup and handles clinical interpretation.
Cortisol AM. Cortisol should peak between 6 and 9 AM. The cortisol awakening response is responsible for a significant portion of morning energy. A blunted AM cortisol below 10 mcg/dL produces the phenomenon people describe as needing two hours and three coffees before functioning. It looks like a sleep problem. It is an adrenal axis problem.
Free T3. TSH normal does not mean thyroid function is optimal. Free T3 is the active form of thyroid hormone at the cellular level. A TSH of 2.8 with a free T3 in the low-normal range can produce fatigue, cold intolerance, and cognitive slowing that is completely invisible on a standard panel.
B12 and homocysteine. Serum B12 above 200 pg/mL passes the standard range. Functional deficiency does not show up in serum B12. It shows up in elevated homocysteine and methylmalonic acid (MMA). Homocysteine above 10 micromol/L with normal serum B12 is a common finding in adults on PPIs, metformin, or with atrophic gastritis. Thorne B-Complex with methylcobalamin is the well-absorbed option.
Fasting insulin. HbA1c normal, fasting glucose normal, and yet insulin is running at 18 mcIU/mL. That is insulin resistance without the markers most physicians check for. At this stage it produces fatigue, brain fog, and abdominal weight gain. A warning before the diagnosis. Function Health includes fasting insulin in its standard panel. Most GP labs do not order it unless the patient is already diabetic.
What to have ready before the results arrive
Most bloodwork trips take less than 15 minutes. Results come back within two to three days. These four supplements address the markers most commonly found low in midlife adults with unexplained fatigue. Having them on hand means starting within hours of seeing the results rather than waiting for a follow-up appointment.
Iron bisglycinate. The form that does not cause constipation. Thorne Iron Bisglycinate at 25 mg daily with a small amount of vitamin C. Take on an empty stomach or with orange juice. Recheck ferritin in six weeks.
Methylcobalamin B-complex. For homocysteine above 10 micromol/L or B12 in the low end of the range. Thorne Basic B with methylcobalamin hits the full B-vitamin complex, including active folate. Recheck homocysteine in eight weeks.
Vitamin D3 with K2. Low vitamin D is among the most common findings on any comprehensive panel in adults who work indoors. Life Extension Vitamin D3 with K2 at 2,000 IU daily. K2 directs calcium to bone rather than arteries. Recheck at 8 to 10 weeks.
Magnesium glycinate. Chronically elevated cortisol depletes magnesium. Low magnesium worsens cortisol regulation and sleep quality. Pure Encapsulations Magnesium Glycinate, 200-400 mg before bed. Under $30 a month and measurably moves sleep quality within two weeks.
The Livium recipe
Tool. Function Health comprehensive panel. One blood draw covers over 100 markers, including ferritin, free testosterone, SHBG, DHEA-S, AM cortisol, free T3, free T4, TSH, homocysteine, MMA, fasting insulin, HbA1c, hs-CRP, vitamin D, and vitamin B12. If already a member of Hone Health, the testosterone side is covered there. Combine the two for the complete picture.
Behavior. When results arrive, triage by the gap between actual value and functional optimal rather than the lab’s reference range. Ferritin at 22 is normal per the lab. It is not optimal. Free testosterone at 44 pg/mL is within range. It is not optimal. These are where most midlife fatigue cases sit.
Threshold. Rerun the panel in three months after addressing the flagged markers. Ferritin moves in four to six weeks of iron supplementation. B12 and homocysteine move in four to eight weeks. Vitamin D takes six to eight weeks. Testosterone and cortisol require clinical co-management and take longer.
Standard lab range versus functional optimal
| Marker | Standard lab range | Functional optimal | Fatigue risk below |
|---|---|---|---|
| Ferritin | 12–300 ng/mL | 50–100 ng/mL | 30 ng/mL |
| Free testosterone (M) | 35–155 pg/mL | 80–130 pg/mL | 50 pg/mL |
| Cortisol AM | 6–23 mcg/dL | 15–20 mcg/dL | 10 mcg/dL |
| Free T3 | 2.0–4.4 pg/mL | 3.0–4.0 pg/mL | 2.5 pg/mL |
| Fasting insulin | 2–25 mcIU/mL | 2–7 mcIU/mL | Above 10 is a signal |
| Homocysteine | <15 micromol/L | <8 micromol/L | Above 10 micromol/L |
| Vitamin D (25-OH) | 20–100 ng/mL | 50–70 ng/mL | 30 ng/mL |
Source: Livium editorial synthesis based on Function Health reference ranges and clinical literature. Individual ranges vary; clinical interpretation required.
Plan of action
- Sign up for Function Health and schedule a draw. The annual membership includes two draws per year.
- When results arrive, check ferritin, homocysteine, fasting insulin, cortisol AM, free T3, and free testosterone first. These are the most commonly suboptimal markers in midlife adults with unexplained fatigue.
- For low ferritin: Thorne Iron Bisglycinate 25 mg daily with vitamin C. Recheck ferritin in six weeks.
- For elevated homocysteine or low B12: Thorne Basic B with methylcobalamin. Recheck homocysteine in eight weeks.
- For low vitamin D: Life Extension D3 with K2 at 2,000 to 4,000 IU daily. Recheck at 8 to 10 weeks.
- For low free testosterone: Hone Health for the clinical workup and treatment conversation.
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FAQs
Is Function Health covered by insurance?
No. It is a direct-pay membership at $499 per year for two comprehensive draws. Many HSA and FSA accounts cover it.
Can a GP run these same markers?
In theory. In practice, insurance will not always cover markers like homocysteine, DHEA-S, or SHBG without a specific diagnosis, and many GPs are not familiar with functional reference ranges. Ordering directly through Function Health is typically faster, cheaper, and more comprehensive.
What if multiple markers come back low?
Address the most impactful first. Ferritin and B12 have the fastest and most predictable response. Testosterone and cortisol require a clinical conversation before intervention. Work through the list one at a time. Fixing everything simultaneously makes it impossible to know what moved the needle.
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