TSH and FT4 Concentrations in Congenital Central Hypothyroidism and Mild Congenital Thyroidal Hypothyroidism

In central hypothyroidism (CeH), free thyroxine (FT4) concentrations are low, whereas thyrotropin (TSH) concentrations may be low, normal, or even slightly elevated due to reduced bioactivity. Congenital CeH (CCeH) may be isolated or part of multiple pituitary hormone deficiencies (MPHD).

We tested our hypotheses that (1) TSH concentrations have a more U-shaped distribution in children with CCeH compared with children with a normally functioning hypothalamic-pituitary-thyroid axis and (2) TSH concentrations in children with CCeH with MPHD are higher compared with children with isolated CCeH. We also studied whether FT4 levels are helpful in distinguishing CCeH from mild congenital hypothyroidism of thyroidal origin (CH-T).

Dutch neonatal screening TSH and first diagnostic TSH and FT4 were analyzed in all children diagnosed with permanent CCeH between 1995 and 2012. Controls were children with T4-binding globulin deficiency. FT4 concentrations in CCeH were compared with those in CH-T with TSH values in the same range as those of CCeH.

We studied 120 children with CCeH (isolated CCeH, n = 50; MPHD, n = 70) and 350 control subjects. Screening TSH concentrations were not significantly different (P = 0.055), but diagnostic TSH values were significantly different between the CCeH group and the control group (P = 0.037). TSH was significantly higher in MPHD compared with isolated CCeH (P = 0.004). FT4 concentrations were significantly lower in CCeH compared with mild CH-T (P < 0.0005).

TSH values in CCeH have a more U-shaped distribution compared with controls with the highest TSH concentrations in MPHD. FT4 levels were significantly lower in CCeH compared with CH-T.