Table 3.

Conditions associated with low/normal TSH and/or low, or even low–normal, free FT4 levels that could lead to erroneous CeH diagnosis or to transient CeH.

Severe form of nonthyroidal illness or sick euthyroid syndrome

Drugs inhibiting TSH secretion: (a) glucocorticoids; (b) dopamine; (c) cocaine; (d) anti-epileptics; (e) anti-psychotics; (f) metformin

Thyrotoxicosis-related conditions: Levothyroxine withdrawal syndrome, prolonged TSH suppression after recovery from thyrotoxicosis

Pregnancy related conditions: (a) Isolated maternal hypothyroxinemia (to be interpreted in the context of trimester-specific FT4 reference ranges for pregnant women). (b) Premature birth (delayed TSH rise in hypothyroid infants)

Genetic conditions: (a) Allen–Herndon–Dudley syndrome (MCT8 gene pathogenic allelic variants); (b) RTHα due to THRA heterozygous mutations; (c) TSHβ allelic variants with conserved bioactivity but lost immunoreactivity of circulating TSH