Screening for Adrenal Insufficiency in Primary Hypothyroidism
No, you do not need to routinely screen for adrenal insufficiency in every patient with primary hypothyroidism (elevated TSH and low free T4), but you must screen in specific high-risk scenarios before initiating levothyroxine.
When Screening Is Mandatory
Screen for adrenal insufficiency before starting levothyroxine in these situations:
- Suspected central (secondary) hypothyroidism – When TSH is low or inappropriately normal with low free T4, indicating pituitary or hypothalamic disease, always measure morning cortisol and ACTH before starting thyroid hormone 1, 2, 3
- Autoimmune hypothyroidism with unexplained features – Screen patients with Hashimoto's thyroiditis who have hypotension, hyponatremia, hyperpigmentation, or hypoglycemia that cannot be fully explained by hypothyroidism alone 1, 4
- Patients on immune checkpoint inhibitors – Those receiving anti-PD-1/PD-L1 therapy or combination immunotherapy who develop hypothyroidism should be evaluated for concurrent hypophysitis and adrenal insufficiency 1
- Known pituitary or hypothalamic disease – Any patient with a history of pituitary tumor, surgery, radiation, or other pituitary hormone deficiencies 1
Why This Matters
Starting levothyroxine before treating adrenal insufficiency can precipitate life-threatening adrenal crisis by accelerating cortisol metabolism 1, 2, 4. The increased metabolic rate from thyroid hormone replacement unmasks or worsens cortisol deficiency 1.
The Clinical Algorithm
Step 1: Identify the Type of Hypothyroidism
- Primary hypothyroidism (elevated TSH >10 mIU/L, low free T4) – This is the most common presentation and typically does NOT require adrenal screening unless red flags are present 1
- Central hypothyroidism (low or inappropriately normal TSH with low free T4) – ALWAYS screen for adrenal insufficiency 1, 2, 3
Step 2: Look for Red Flags in Primary Hypothyroidism
Even with elevated TSH, screen for adrenal insufficiency if the patient has:
- Unexplained hypotension (systolic BP <100 mmHg) 1
- Hyponatremia (sodium <135 mEq/L) 1
- Hyperpigmentation 1
- Unexplained hypoglycemia 1
- History of other autoimmune conditions (type 1 diabetes, vitiligo, pernicious anemia) 1, 4
- Symptoms disproportionate to thyroid dysfunction (severe fatigue, salt craving, weight loss despite hypothyroidism) 1
Step 3: Screening Tests When Indicated
- Morning (8 AM) serum cortisol and ACTH – Obtain before starting levothyroxine 1
- Cosyntropin stimulation test (250 µg) if morning cortisol is low or equivocal – Peak cortisol <500 nmol/L is diagnostic 1
- 21-hydroxylase antibodies – To identify autoimmune adrenal insufficiency (Addison's disease) 1
Step 4: Treatment Sequence
If adrenal insufficiency is confirmed:
- Start hydrocortisone 20 mg in the morning and 10 mg in the afternoon 1
- Wait at least one week before initiating levothyroxine 1
- Never start thyroid hormone first 1, 2, 4
Common Clinical Scenarios
Scenario 1: Classic Primary Hypothyroidism
A 45-year-old woman with TSH 25 mIU/L, free T4 0.6 ng/dL, positive anti-TPO antibodies, fatigue, weight gain, and normal blood pressure.
Action: No adrenal screening needed. Start levothyroxine 1.6 mcg/kg/day 1
Scenario 2: Primary Hypothyroidism with Red Flags
A 50-year-old man with TSH 18 mIU/L, free T4 0.7 ng/dL, blood pressure 90/60 mmHg, sodium 130 mEq/L, and unexplained hyperpigmentation.
Action: Measure morning cortisol and ACTH before starting levothyroxine. If adrenal insufficiency is confirmed, start hydrocortisone first 1, 4
Scenario 3: Central Hypothyroidism
A 60-year-old woman with TSH 1.2 mIU/L (inappropriately normal), free T4 0.5 ng/dL, history of pituitary macroadenoma.
Action: Always screen for adrenal insufficiency with morning cortisol and ACTH. Start hydrocortisone before levothyroxine if deficient 1, 2, 3
Key Pitfalls to Avoid
- Never assume normal blood pressure excludes adrenal insufficiency – Some patients maintain adequate BP until stressed 1
- Don't rely on TSH alone to distinguish primary from central hypothyroidism – An elevated TSH can occasionally occur in central hypothyroidism, though this is rare 2
- Don't miss polyglandular autoimmune syndrome – Patients with Hashimoto's thyroiditis have increased risk of concurrent Addison's disease 1, 4
- Don't start levothyroxine in hospitalized patients without considering non-thyroidal illness – Acute illness can transiently suppress TSH and alter thyroid tests 1
Evidence Quality
The recommendation to screen for adrenal insufficiency before starting levothyroxine in central hypothyroidism or suspected concurrent adrenal disease is based on clinical experience and case reports demonstrating adrenal crisis when thyroid hormone is started first 1, 2, 4. While randomized trials are lacking (and would be unethical), the physiologic rationale is sound and the consequences of missing adrenal insufficiency are severe 1.
Bottom Line
For typical primary hypothyroidism (high TSH, low T4, no red flags): No screening needed—start levothyroxine.
For central hypothyroidism or primary hypothyroidism with unexplained hypotension, hyponatremia, or other concerning features: Screen for adrenal insufficiency first and treat with hydrocortisone before starting levothyroxine 1, 2, 4.