Table 3.

Conditions with biochemical features that could lead to an erroneous CeH diagnosis

Non-thyroidal illness

Isolated maternal hypothyroxinemia (to be interpreted in the context of trimester-specific FT4 reference ranges for pregnant women)

L-T4 withdrawal syndrome

Recovery from thyrotoxicosis

Technical assay problems or interference, or defects in thyroxine-binding globulin (TBG defects in case of total T4 determination or calculation of FT4 index)

Drugs reducing TSH secretion (glucocorticoids, dopamine, cocaine, anti-epileptics or anti-psychotics, metformin)

Premature birth (delayed TSH rise in hypothyroid infants)

Allan-Herndon-Dudley syndrome (MCT8 mutations)

THRA mutations (RTHa)

TSHβ mutations with conserved bioactivity but lost immunoreactivity of circulating TSH