Diagnostics

The most common lab misinterpretation in primary care

Thyroid dysfunction affects roughly 10% of adults, and it is frequently missed or misdiagnosed because most evaluations rely on TSH alone. TSH is a screening test, not a comprehensive assessment. A normal TSH does not exclude thyroid problems.

A complete panel

  • TSH: the pituitary signal to the thyroid. Elevated when the thyroid is underperforming; suppressed when it’s overactive.
  • Free T4: the primary hormone the thyroid produces, unbound and active.
  • Free T3: the more biologically active form. T4 converts to T3 in the periphery, but the conversion can be impaired.
  • Reverse T3: an inactive isomer that can rise in illness, stress, or metabolic dysfunction, blocking active T3 at receptors.
  • Thyroid antibodies (TPO, thyroglobulin): identify autoimmune thyroid disease (Hashimoto’s, Graves’), which can be present with normal hormone levels for years.

What “normal” ranges miss

The standard TSH reference range (roughly 0.4–4.5 mIU/L) includes people who are frankly symptomatic. Many patients with TSH in the 2.5–4.5 range have subclinical hypothyroidism symptoms that respond to treatment or careful watching. The context — symptoms, antibodies, other hormone results — matters more than a single value.

Common symptoms of underactive thyroid

  • Fatigue disproportionate to sleep
  • Cold intolerance
  • Weight gain resistant to diet changes
  • Dry skin, thinning hair (particularly the outer eyebrows)
  • Constipation
  • Depression or cognitive slowing
  • Menstrual irregularities
  • Elevated cholesterol

Common symptoms of overactive thyroid

  • Unintended weight loss
  • Heat intolerance, sweating
  • Palpitations or racing heart
  • Anxiety, agitation
  • Tremor
  • Insomnia
  • Diarrhea or frequent bowel movements

Treatment approaches

  • Levothyroxine (T4): standard first-line. Works well for most.
  • Liothyronine (T3) or T4/T3 combinations: appropriate for patients who don’t feel well on T4 alone, particularly those with impaired conversion.
  • Natural desiccated thyroid: an older formulation containing T4 and T3 from porcine sources. Effective for many; requires the same monitoring as any thyroid therapy.
  • For Hashimoto’s: treating hormones plus addressing autoimmune contributors (gluten, iron, selenium, vitamin D status, and lifestyle factors when relevant).

Dose adjustments require follow-up labs at 6–8 weeks and are individualized to symptoms and thyroid values.

What causes thyroid dysfunction

Autoimmunity (most common in developed countries), iodine deficiency (globally more common), post-partum shifts, medications, radiation exposure, viral illness, and genetic factors. In practice, we identify a cause when possible and treat regardless.

Next steps

If thyroid symptoms have been dismissed or if you’ve been told your TSH is normal despite persistent issues, a complete panel is the right diagnostic. Book a consultation.