Guidelines for Hypothyroidism: Diagnosis and Management
Diagnosis
Hypothyroidism should be diagnosed biochemically with elevated TSH and low free T4, not based on symptoms alone 1. Thyroid hormones should never be used to treat symptoms suggestive of hypothyroidism without biochemical confirmation 1.
When to Test
- Do not screen asymptomatic general population 2
- Screen patients over age 60 1
- Test high-risk patients: those with type 1 diabetes, autoimmune disorders, family history of thyroid disease, pregnant women or those planning pregnancy with risk factors, patients on amiodarone or immune checkpoint inhibitors 1, 2
Diagnostic Criteria
- Overt hypothyroidism: Elevated TSH + Low free T4
- Subclinical hypothyroidism: Elevated TSH + Normal free T4 and T3
Treatment Initiation
L-thyroxine (levothyroxine) monotherapy is the only recommended treatment for hypothyroidism 1.
What NOT to Use
- Do not use desiccated thyroid hormone 1
- Do not use L-thyroxine/L-triiodothyronine combinations, especially in pregnancy 1
- Do not use TRIAC (tiratricol) 1
- Do not use iodine supplementation or kelp in iodine-sufficient areas 1
Dosing Strategy
Overt Hypothyroidism
Young healthy adults (<50 years): Start with full replacement dose of 1.6 µg/kg daily based on ideal body weight 1.
Older adults (>50-60 years) without cardiac disease: Start with 50 µg daily 1.
Patients with coronary artery disease or cardiac risk: Start low (12.5-25 µg daily) and titrate slowly 3.
Subclinical Hypothyroidism
Initial dosing: 25-75 µg daily, titrated based on degree of TSH elevation 1:
- TSH 4.0-8.0 mIU/L: Start 25 µg
- TSH 8-12 mIU/L: Start 50 µg
- TSH >12 mIU/L: Start 75 µg
Treat subclinical hypothyroidism when:
- TSH >10 mIU/L (treat all patients) 4
- Any TSH elevation in pregnancy or women planning pregnancy 1, 5, 4
- TSH ≤10 mIU/L if symptomatic, infertile, positive anti-TPO antibodies, or goiter present 4
Avoid treatment in patients >85 years with TSH ≤10 mIU/L 4.
Administration
L-thyroxine must be taken with water 30-60 minutes before breakfast OR at bedtime 4 hours after the last meal 1. This timing is critical—taking it within 30 minutes of breakfast significantly reduces absorption 1.
Key Administration Points
- Store at 20-25°C (68-77°F), protected from light and moisture 1
- Do not take with substances that interfere with absorption (calcium, iron, proton pump inhibitors, soy) 1
- For enteral feeding: crush tablet, suspend in water, stop feeding 1 hour before and after dose 1
- IV dosing: Use 70% of oral dose if patient cannot take oral medication 1
Monitoring
Non-Pregnant Patients
Check TSH 4-8 weeks after starting treatment or dose changes 1.
Target TSH: Within normal reference range (0.5-2.0 mIU/L) 4. Evidence does not support targeting specific TSH values within the normal range, except in pregnancy [1, @27@].
Once stable: Check TSH annually 2.
Drug Interactions
Remeasure TSH within 4-8 weeks when starting medications that affect levothyroxine bioavailability or metabolism 1. This is a Grade A recommendation.
Pregnancy Management
Pregnancy requires aggressive TSH monitoring and dose adjustments 1.
TSH Targets in Pregnancy
Monitoring Schedule
- Check TSH immediately after conception 1
- Monitor every 4 weeks during first half of pregnancy 1
- Check at least once between 26-32 weeks gestation 1
Dose Adjustment
Women with hypothyroidism who become pregnant should increase their weekly levothyroxine dosage by 30% (take one extra dose twice per week) 3. This should be done immediately upon conception.
When to Refer to Endocrinology
Refer patients in these categories 1:
- Children and infants
- Difficult to maintain euthyroid state
- Pregnancy or women planning conception
- Cardiac disease
- Goiter, nodule, or structural thyroid changes
- Other endocrine disorders (adrenal, pituitary)
- Unusual thyroid function test patterns
- Unusual causes of hypothyroidism (medication-induced, malabsorption)
Common Pitfalls
Persistent Elevated TSH Despite Treatment
Check for:
- Poor compliance (most common)
- Incorrect timing of administration (taking with food or interfering substances)
- Malabsorption (celiac disease, atrophic gastritis, inflammatory bowel disease)
- Drug interactions (calcium, iron, PPIs, estrogen, rifampin, phenytoin, carbamazepine)
- Increased requirements (pregnancy, weight gain, aging)
Over-Replacement
Avoid suppressed TSH (<0.1 mIU/L) as this increases risk of atrial fibrillation and osteoporosis 4. Over-replacement is common in clinical practice and should be actively avoided.
Resuming Therapy After Interruption
Patients resuming levothyroxine after interruption <6 weeks without cardiac events or significant weight loss may resume their full previous dose 1.