Laboratory Monitoring in Panhypopituitarism on Hormone Replacement Therapy
Monitor thyroid function tests (TSH and free T4) every 1-2 weeks initially after starting replacement, then before each clinical visit; check early morning cortisol and ACTH monthly for 6 months, then every 3 months for 6 months, then every 6 months thereafter; and assess sex hormones, IGF-1, prolactin, and metabolic parameters at regular intervals based on clinical response. 1, 2
Initial Baseline Assessment
Before initiating hormone replacement therapy, obtain a complete pituitary axis evaluation including: 1, 2
- 9 AM cortisol and ACTH (or random if patient is acutely unwell and treatment cannot be delayed) 1
- TSH and free T4 to assess thyroid axis 1, 2
- LH, FSH, testosterone (in men), estradiol (in premenopausal women) for gonadal axis 1, 2
- IGF-1 to evaluate growth hormone status 1, 2
- Prolactin levels 1, 2
- Glucose and HbA1c for metabolic assessment 2
- Electrolytes to exclude mineralocorticoid deficiency (though rarely necessary in hypopituitarism) 1
Monitoring Schedule After Initiating Replacement
Thyroid Function Monitoring
- Check TSH and free T4 every 1-2 weeks initially after starting thyroid hormone replacement 1
- Continue frequent monitoring until stable, then transition to routine follow-up 1
- Critical caveat: Always replace cortisol for at least 1 week before initiating thyroxine to avoid precipitating adrenal crisis 1, 2
Adrenal Function Monitoring
- Early morning ACTH and cortisol monthly for the first 6 months 2
- Every 3 months for the next 6 months 2
- Every 6 months thereafter for at least 1 year, then adjust based on clinical stability 2
Growth Hormone Axis
- Monitor IGF-1 levels at regular intervals if on growth hormone replacement 2
- If assessing for GH deficiency post-surgery or post-treatment, wait at least 6-12 months before dynamic testing as recovery is often delayed 2
Gonadal Axis
- Testosterone levels in men and estradiol in premenopausal women should be monitored periodically to ensure adequate replacement 1, 2
- Check LH and FSH if adjusting gonadotropin replacement 1
Metabolic Parameters
- Regular glucose and HbA1c monitoring to assess glycemic control 2
- Electrolytes periodically, though mineralocorticoid replacement is rarely necessary in hypopituitarism 1
Critical Interpretation Principles
Central Hypothyroidism Pattern
- Low free T4 with low or normal TSH (not elevated like primary hypothyroidism) 2
- TSH cannot be used alone to monitor adequacy of replacement in central hypothyroidism 2
Central Adrenal Insufficiency Pattern
- Low cortisol with low or normal ACTH (not elevated like primary adrenal insufficiency) 2
- Random cortisol <150 nmol/L or 9 AM cortisol <250 nmol/L suggests deficiency 1
Hypogonadotropic Hypogonadism Pattern
- Low testosterone/estradiol with low or normal FSH and LH 2
Essential Clinical Pitfalls to Avoid
Never start thyroid hormone replacement before ensuring adequate cortisol replacement, as this can precipitate life-threatening adrenal crisis 1, 2. The adrenal axis must always be addressed first 3.
Do not use TSH alone to guide thyroid replacement dosing in central hypothyroidism—free T4 is the primary monitoring parameter 2.
Ensure patient education on "sick day rules" and provide prescription for intramuscular steroids for emergency use 1. Consider alert card or medical bracelet 1.
MRI of the sella with pituitary protocol should be performed if structural cause is suspected or to monitor pituitary changes over time 2, 3.