Thyroid Function
Your thyroid sets your metabolic speed. Track TSH, Free T3, and Free T4 to catch under- or overactive thyroid long before symptoms escalate.
Why thyroid function matters
The thyroid is a small gland at the base of your neck that produces hormones regulating your metabolism, body temperature, energy production, and weight. When it underperforms (hypothyroidism) or overperforms (hyperthyroidism), the effects ripple through nearly every system — fatigue, weight changes, temperature sensitivity, hair thinning, mood shifts, and irregular heart rate among them.
Thyroid dysfunction is common and frequently underdiagnosed because early symptoms are vague and overlap with stress, poor sleep, or aging. Testing TSH alongside Free T3 and Free T4 gives a fuller picture than TSH alone, because it shows not just whether the pituitary is calling for more hormone, but whether the thyroid is actually delivering it.
- TSH is the pituitary's signal to the thyroid — the most sensitive first indicator of dysfunction.
- Free T4 is the main hormone the thyroid produces; it reflects hormone supply.
- Free T3 is the active form your cells actually use for energy and metabolism.
- Subclinical thyroid dysfunction can persist for years before a single annual test catches it.
What we measure
Reference ranges are general guidelines. VitalDrop emphasizes your personal trend over time rather than a single in-or-out snapshot.
TSH (Thyroid Stimulating Hormone)
The pituitary hormone that tells the thyroid to produce T3 and T4. Elevated TSH suggests underactive thyroid.
Free T3 (female only)
The biologically active thyroid hormone that drives cellular metabolism and energy production.
Free T4 (female only)
The primary hormone secreted by the thyroid; converted into T3 in tissues throughout the body.
What affects these markers
- Iodine, selenium, and zinc intake
- Autoimmune conditions (Hashimoto's, Graves')
- Chronic stress and elevated cortisol
- Pregnancy and postpartum changes
- Certain medications
How VitalDrop helps
- Monthly tracking catches subclinical shifts that fall inside the 'normal' range but trend the wrong direction.
- TSH with Free T3/T4 reveals both the signal and the thyroid's actual output.
- Trend lines help distinguish a temporary fluctuation from a sustained pattern.
- Physician review flags results needing clinical follow-up.
Reviewed by Dr. Hassan Nasser
Medical Director — www.detroitfacemd.com
Board-certified facial plastic & reconstructive surgeon; clinical reviewer for VitalDrop laboratory insights. Verified at www.detroitfacemd.com
This content has been clinically reviewed by a board-certified physician for medical accuracy. It is educational and not a substitute for personalized medical advice, diagnosis, or treatment. Always consult your own clinician with questions about your results.
Frequently asked questions
TSH is a signal from the pituitary, not a direct measure of thyroid output. Someone can have a TSH within range while Free T3 or T4 are low (or converting poorly). Measuring all three gives a more complete picture of whether the thyroid is both being asked to produce and actually delivering adequate hormone.
Scientific references
Content informed by peer-reviewed guidelines and literature.
- 1.2014 ATA Guidelines for Diagnosis & Management of Thyroid Disease. American Thyroid Association / Thyroid (2014).
- 2.Subclinical Thyroid Dysfunction: A Systematic Review. JAMA (2019).
- 3.Free T3 and Free T4 in the Evaluation of Thyroid Function. Clinical Chemistry (2021).
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