Download Differential Diagnosis of Hyperthyroxinemia and Nonsuppressed TSH.

Figure. Differential Diagnosis of Hyperthyroxinemia and Nonsuppressed TSH
High Total or Free T4 (analogue method)
Normal/high TSH
Rule out levothyroxine therapy, acute
non-thyroidal illness, and drug effects
Free T4, Direct Dialysis (DFT4)
and TSH
Normal DFT4
Normal/high TSH
High DFT4
Normal/high TSH
Hyperthyroxinemia
not confirmed
Suspect resistance to
thyroid hormone (RTH)
Resistance to
Thyroid Hormone (RTH)
Mutation Analysis
(THRB gene mutation)
Suspect analytical
interference
T4 Antibody
T4 Binding Proteins
TSH Antibody
TSH, with HAMA
Treatment
No abnormalities detected
Negative
Positive
RTH very likely
Suspect TSH-secreting
pituitary tumor
Possible RTH without
THRB mutation
(15% of cases)
Alpha Subunit
and TSH
Alpha subunit:TSH ratio >1
Consider THRB
mutation testing on
1st degree relatives
Alpha subunit:TSH ratio <1
T3 Suppression Test
(unless contraindicated)
TSH not
suppressed
TSH partially
suppressed
TSH-secreting
pituitary adenoma
probable
Analytical interference in the direct dialysis free T4 and TSH assays could result from benign conditions such as abnormal T4 binding
proteins (eg, familial dysalbuminemic hyperthyroxinemia), autoantibodies to T4 or TSH, or exposure to mouse monoclonal antibodies
resulting in production of human anti-mouse antibodies (HAMA). Adapted from references 1 and 2.
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Content reviewed 12/2012