Hypothyroidism

Hypothyroidism

Evaluation & Management of Overt & Subclinical Hypothyroidism

Check TSH + Free T4

  • TSH ↑ + Free T4 ↓ → Overt Hypothyroidism
  • TSH ↑ + Free T4 normal → Subclinical Hypothyroidism (SCH)

If Overt Hypothyroidism

  • Start Levothyroxine:
    • Typical starting dose: 1.6 mcg/kg/day (younger, healthy adults).
    • Elderly or cardiac disease: start 25–50 mcg/day, titrate as tolerated.
  • Recheck TSH in 6–8 weeks.
  • Goal: Normalize TSH (0.5–4.5), with a target closer to 2.5 if pregnant.

If Subclinical Hypothyroidism (TSH ↑, T4 normal)

Treat if:

  • TSH ≥10 mIU/L.
  • TSH 4.5–9.9 mIU/L with one of the following:
    • Symptoms of hypothyroidism.
    • Positive anti-TPO antibodies.
    • Goiter.
    • Pregnancy or planning pregnancy.
    • Age <65 with risk factors (CV disease, metabolic syndrome, infertility).

Otherwise:

  • Observe + recheck TSH in 6–12 months.

Monitoring

  • Recheck TSH 6–8 weeks after dose changes, then every 6–12 months once stable.

Referral Indications:

Persistent TSH elevation despite adequate levothyroxine dose and adherence.

Suspected central hypothyroidism (low/normal TSH with low free T4).

Goiter or thyroid nodules

Pregnancy with hypothyroidism (early / urgent)

New/worsening symptoms despite proper treatment (early / urgent)

Suspicious features (Urgent):

Rapidly enlarging goiter

Hard/fixed thyroid mass

Compressive symptoms

Cervical lymphadenopathy

Personal/family history of thyroid cancer

Prior head/neck radiation

Important Considerations (Levothyroxine Dosing) :

  • Weight for calculation:
    • In patients with BMI <30, the levothyroxine dose can be calculated using actual body weight (ABW) at ~1.6 mcg/kg/day.
    • In patients with BMI ≥30, using actual weight risks overdosing. In this case, dose should be based on Ideal Body Weight (IBW), calculated as:
      • Men: 50 kg + 0.9 × (height in cm − 152)
      • Women: 45.5 kg + 0.9 × (height in cm − 152)
    • An online calculator is available via https://www.mdcalc.com/calc/68/ideal-body-weight-adjusted-body-weight
  • Rounding doses:
    • Levothyroxine tablets are available in increments of 25 mcg (25, 50, 75, 100, 125, etc.).
    • After calculating the initial dose, round to the nearest available strength.
    • If the dose lies midway (e.g., 84 mcg → between 75 and 100):
      • Younger, healthy patients: round up.
      • Elderly or patients with cardiac disease: round down.

 

 

Prepared & reviewed by: Dr. Fahad Saad Almutairi, Dr. Bader Thuwaini Alanazi