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Answer · biomarkers

Persistent fatigue workup — what should be tested?

Short answer

Persistent fatigue workup screens thyroid, iron and B12, testosterone, sleep apnea, insulin resistance, and inflammation. Highest-yield drivers vary by sex and age.

Reviewed by Dr. Laura PurdyMay 29, 2026

Full answer

Persistent fatigue workup is one of the most common — and most under-investigated — adult complaints. The provider-reviewed workup screens systematically: thyroid (TSH, Free T4, Free T3), hematology (CBC, ferritin, B12, folate), hormones (total and free testosterone in men, estradiol/progesterone in perimenopausal women, DHEA-S, cortisol), metabolic (fasting insulin, A1C, fasting glucose), inflammation (hs-CRP, ferritin as APR), and sleep architecture context. oMeds biomarker review surfaces the highest-yield drivers first and avoids the trap of chasing one marker in isolation.

Educational. Not a substitute for individualized provider review.

References & sources
  • Symptoms & side effects — Primary source · oMeds
  • Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29

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Related answers

Iron deficiency anemia?
Iron deficiency anemia is low hemoglobin from depleted iron stores. Ferritin is the most sensitive early marker; hemoglobin falls late. Common in menstruating women and athletes.
What is vitamin B12?
B12 is essential for red cell formation and neurologic function. Vegans, older adults, and long-term users of PPIs or metformin are at risk. Symptoms can precede serum-level abnormalities.
What is TSH?
TSH (thyroid stimulating hormone) is the pituitary signal that drives thyroid hormone production. It is the most sensitive screening marker of thyroid function. Conventional ranges run roughly 0.4–4.5 mIU/L; many optimization frameworks target the lower-mid range when reading TSH with free T3, free T4, and TPO antibodies.
Primary source
Symptoms & side effects