Hypothyroidism in Primary Care: Fast Dx → Confident Treatment

Typical lab pattern

• TSH: high

• Free T4: low

• T3: normal or low (often not necessary to diagnose)

Treatment goals

1. Reverse hypothyroid symptoms

2. Normalize TSH (and FT4)

3. Reduce goiter size (if present)

First-Line: Levothyroxine (T4)

Why: Physiologic, stable half-life (~7 days), predictable conversion to T3 in tissues.

How to take (teach every time):

• Empty stomach, first thing AM, with water, 30–60 min before food/coffee.

• Separate from iron, calcium, magnesium, multivitamins, bile-acid resins, sucralfate, PPI timing, etc., by ≥4 hours.

• Consistency matters: same brand/generic manufacturer if possible (document the product).

Brands: Synthroid®, Levoxyl®, Tirosint® (capsules/solution; often not covered).
Tablets commonly covered: 25, 50, 75, 88, 100, 112, 125, 137, 150, 175, 200 mcg.

How I Start the Dose 

Pick ONE approach and be consistent:

• Healthy, <60 y, no CAD: ~1.6 mcg/kg/day (actual body weight) or start 50–75 mcg daily and titrate.

• Older adults or CAD risk: 12.5–25 mcg daily, go slow.

• Subclinical hypothyroidism (TSH high, FT4 normal): shared decision-making; often start 25–50 mcg if treating (e.g., TSH ≥10, symptoms, +TPO, goiter, pregnancy plans).

• Pregnancy (known hypothyroid): increase total weekly dose by ~20–30% immediately (e.g., 2 extra tablets/week) and check TSH q4 weeks in 1st half of pregnancy.

Monitoring & Titration

• Recheck TSH (± FT4) 6–8 weeks after any dose change.

• Adjust by 12.5–25 mcg to next tablet strength (e.g., 50 → 62.5–75 → 88 mcg).

• Target TSH: generally the lab’s normal range; many aim mid-normal (e.g., 0.5–2.5) once symptoms resolve.

• Once stable, recheck every 6–12 months (or sooner with symptoms, pregnancy, new meds).

Pearl: TSH lags—don’t recheck earlier than 6 weeks after a change.

Adjunct: Liothyronine (T3) — When (and if) to Consider

• Brand: Cytomel®

• Who: Select patients still symptomatic despite normalized TSH/FT4, after ruling out other causes (sleep, anemia, depression, OSA, etc.).

• How: Small, split dosing (e.g., 5 mcg AM + 5 mcg mid-day), titrate by 5 mcg; monitor TSH, FT4, and total T3.

• Cautions: Short half-life → peaks; arrhythmia/angina risk; avoid in significant CAD or older/frail patients.

• Trial: 3–6 months; stop if no clear benefit.

Desiccated Thyroid (T4/T3 combos)

• Examples: Armour®, NP Thyroid®

• Not preferred to start due to variable T3 content, non-physiologic ratios, and monitoring complexity.

• If a patient strongly prefers and is stable, educate on risks and monitor carefully; consider conversion to levothyroxine when feasible.

Practical Gotchas (and fixes)

• Biotin can falsely lower TSH / raise T4/T3 → hold 48 hours before labs.

• Iron/calcium bind LT4 → separate by ≥4 hours.

• New meds (amiodarone, lithium, PPIs, sertraline, antiepileptics) can alter dose needs.

• Weight change, pregnancy, menopause → reassess dose.

• Goiter regression is slow; counsel expectations (months).

 Quick FAQs

• How fast should patients feel better? Energy/skin/bowel can improve within 2–6 weeks; weight and hair changes take longer.

• Subclinical hypothyroidism—treat? Reasonable if TSH ≥10, +TPO, goiter, symptomatic, or pregnancy plans. Otherwise, recheck in ~3 months before deciding.

Education only; use clinical judgment and local guidelines.

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