What is the workup for postpartum hyperthyroidism?

Workup for Postpartum Hyperthyroidism

Measure TSH and free T4 (FT4) to confirm biochemical hyperthyroidism, then obtain TSH receptor antibodies (TRAb/TBIAb) and radioactive iodine uptake (RAIU) to distinguish postpartum thyroiditis from Graves' disease. 1, 2

Initial Laboratory Evaluation

The essential first step is biochemical confirmation with TSH and FT4 levels. 1, 2

• TSH will be suppressed and FT4 elevated in both postpartum thyroiditis and Graves' disease 1
• Add T3 measurement if symptoms are severe but FT4 elevation is minimal, as T3 toxicosis can occur particularly in Graves' disease 1
• Obtain antithyroid peroxidase (anti-TPO) antibodies to confirm the diagnosis and assess risk of permanent hypothyroidism 1

Critical Distinguishing Tests

The key to management is differentiating postpartum thyroiditis (destructive, self-limited) from Graves' disease (requires antithyroid treatment):

TSH Receptor Antibodies (TRAb/TBIAb)

• Obtain TRAb testing if clinical features suggest Graves' disease (ophthalmopathy, persistent symptoms beyond 6 weeks, or family history) 2
• Positive TRAb strongly suggests Graves' disease, though research shows TRAb can be positive in up to 52% of postpartum thyroiditis cases with low RAIU 3
• The presence and level of TRAb helps predict disease course: higher levels correlate with true Graves' disease requiring treatment 3

Radioactive Iodine Uptake (RAIU)

• RAIU is the definitive test to distinguish these conditions after ensuring adequate iodine restriction for 1 week 3
• RAIU <10% indicates destructive thyroiditis (postpartum thyroiditis) - no treatment needed 3, 4
• RAIU >40% indicates Graves' disease - requires antithyroid medication 3, 4
• RAIU 10-40% is intermediate and requires clinical judgment, repeat testing, or endocrine consultation 3
• Check urinary iodine excretion if RAIU is low, as excess dietary iodine can suppress uptake and confound interpretation 3

Physical Examination Findings

Look specifically for features that distinguish Graves' disease from thyroiditis:

• Ophthalmopathy (proptosis, lid lag, periorbital edema) is diagnostic of Graves' disease and warrants immediate endocrine referral 1, 5
• Thyroid bruit indicates Graves' disease with increased vascularity 1
• Painless goiter can occur in both conditions but is more common in postpartum thyroiditis 6
• Assess for signs of thyroid storm (fever, tachycardia out of proportion to fever, altered mental status) which requires immediate treatment 1

Timeline Considerations

The timing of symptom onset helps predict etiology:

• Hyperthyroidism at 1-3 months postpartum most commonly represents destructive thyroiditis 4, 7
• Hyperthyroidism at 3-6 months postpartum more likely represents Graves' disease 4, 5
• However, overlap exists: research shows Graves' disease can be masked by concurrent thyroiditis in the early postpartum period 3

Monitoring Strategy

Serial monitoring is essential regardless of initial diagnosis:

• Recheck TSH and FT4 every 2-3 weeks to detect spontaneous resolution or transition to hypothyroidism 1, 2
• If hyperthyroidism persists beyond 6 weeks, repeat RAIU as initial thyroiditis may unmask underlying Graves' disease 2, 3
• Monitor for hypothyroid phase which occurs in 76% of postpartum thyroiditis cases and may require levothyroxine 3, 7

Common Pitfalls to Avoid

• Do not start antithyroid drugs empirically without RAIU confirmation, as they are ineffective and potentially harmful in destructive thyroiditis 2
• Do not assume low TRAb excludes Graves' disease - clinical features and RAIU are more definitive 3
• Do not dismiss symptoms as "normal postpartum changes" without biochemical evaluation, especially in women with goiter or prior thyroid disease 1
• Do not perform RAIU without adequate iodine restriction, as dietary iodine can falsely suppress uptake 3
• Remember that up to 46% of women with initial thyroiditis will develop true Graves' hyperthyroidism 4-9 months postpartum, requiring continued surveillance 3