How should a primary care provider manage overt hypothyroidism in patients, considering factors such as age, cardiac disease, and comorbidities like diabetes and hypertension?

Primary Care Management of Overt Hypothyroidism

Initial Assessment and Confirmation

Before starting treatment, confirm the diagnosis with repeat TSH and free T4 testing after 3-6 weeks, as 30-60% of elevated TSH values normalize spontaneously. 1 This critical step prevents unnecessary lifelong treatment in patients with transient thyroiditis 1. Measure anti-TPO antibodies to identify autoimmune etiology (Hashimoto's thyroiditis), which predicts higher progression risk and justifies treatment 1.

Starting Levothyroxine: Age and Cardiac Risk Stratification

Young, Healthy Patients (<70 years, no cardiac disease)

• Start with full replacement dose of 1.6 mcg/kg/day 1, 2
• This approach rapidly normalizes thyroid function and prevents prolonged hypothyroid symptoms 1
• Most young patients tolerate full replacement without complications 3, 4

Elderly Patients (>70 years) or Those with Cardiac Disease

Start with 25-50 mcg/day and titrate slowly every 6-8 weeks 1, 2, 5. This is non-negotiable for cardiac safety. Rapid normalization can unmask or worsen cardiac ischemia, precipitate myocardial infarction, heart failure, or fatal arrhythmias 1, 5. The increased cardiac workload from thyroid hormone can decompensate underlying coronary disease 6, 5.

For patients with recent acute coronary syndrome or unstable angina, start even lower (12.5-25 mcg/day) and increase by 12.5 mcg increments 1. Monitor for new angina, palpitations, or dyspnea at each visit 1.

Patients with Multiple Comorbidities (Diabetes, Hypertension)

• Start with 25-50 mcg/day regardless of age 1
• Hypothyroidism causes insulin resistance and can worsen glycemic control 7
• Treatment improves metabolic parameters but must be gradual to avoid cardiac stress 1

Critical Safety Check: Rule Out Adrenal Insufficiency

Before starting levothyroxine in any patient with suspected central hypothyroidism or autoimmune disease, rule out adrenal insufficiency 1, 4. Starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 1, 4. If adrenal insufficiency is present or suspected, start physiologic dose steroids 1 week prior to levothyroxine 1.

Monitoring and Dose Titration

• Recheck TSH and free T4 every 6-8 weeks after any dose change 1, 2, 7
• Adjust dose by 12.5-25 mcg increments based on TSH results 1, 2
• Use smaller increments (12.5 mcg) for elderly or cardiac patients 1
• Target TSH: 0.5-4.5 mIU/L with normal free T4 1, 4
• Once stable, monitor TSH annually 1, 7

Administration Instructions

Levothyroxine must be taken on an empty stomach, 30-60 minutes before breakfast with a full glass of water 2, 8. Take at least 4 hours apart from iron, calcium supplements, or antacids, which interfere with absorption 2. Ensure patients understand this is lifelong therapy requiring consistent daily dosing 8.

Common Pitfalls to Avoid

Approximately 25% of patients are unintentionally overtreated with TSH fully suppressed 1, 4. This increases risk for atrial fibrillation (5-fold in patients ≥45 years), osteoporosis, fractures, and cardiovascular mortality 1, 9. Regular monitoring prevents this dangerous complication.

Never start full replacement dose in elderly patients with cardiac disease—this can precipitate myocardial infarction or fatal arrhythmias 1, 5. Always start low and go slow in this population.

Don't treat based on a single elevated TSH without confirmation 1. Many cases represent transient thyroiditis in recovery phase or non-thyroidal illness 1, 5.

Special Populations

Pregnant Women or Planning Pregnancy

Start treatment immediately with any TSH elevation 1. Target TSH <2.5 mIU/L before conception 1. Untreated hypothyroidism increases risk of preeclampsia, low birth weight, miscarriage, and permanent neurodevelopmental deficits in offspring 1, 7. Levothyroxine requirements increase 25-50% during pregnancy—increase dose immediately upon pregnancy confirmation 1.

Patients on Immunotherapy

Thyroid dysfunction occurs in 6-20% of patients on checkpoint inhibitors 1. Consider treatment even for subclinical hypothyroidism if fatigue or other symptoms present 1. Continue immunotherapy in most cases—thyroid dysfunction rarely requires treatment interruption 1.

When to Refer

Refer to endocrinology for:

• Central hypothyroidism (low TSH with low free T4) 4
• Persistently elevated TSH despite adequate replacement dose (suggests malabsorption or non-compliance) 4
• Pregnant patients requiring optimization 1
• Patients with thyroid cancer requiring TSH suppression 1
• Cardiac patients requiring complex titration 5