Treatment of Congenital Iodine-Deficiency with Low fT4 and Low or Normal TSH (Central CH)
When congenital iodine-deficiency presents with a low serum fT4 and a TSH that is low, normal, or only slightly elevated, the pattern points to central congenital hypothyroidism (central CH). This scenario requires a distinct management approach — and a critical safety step before thyroid hormone replacement is started.
Clinical Scenario
Low serum fT4 with low, normal, or slightly elevated serum TSH (central CH), in a neonate with intact adrenal function and no coexistent central adrenal insufficiency. If central adrenal insufficiency cannot be excluded, it must be addressed before thyroid hormone is initiated.
Treatment Approach
Once intact adrenal function is confirmed, oral levothyroxine (LT4) once daily is initiated as early as possible after birth. The initiation strategy differs based on the severity of the fT4 deficit — more severe central CH is approached differently than milder presentations. The full dosing algorithm and thresholds are available in the structured protocol.
Treatment Goal
Serum fT4 should be brought rapidly within the normal range and then maintained in the upper half of the age-specific fT4 reference interval.
References
DOI: 10.1089/thy.2020.0333
- If the serum fT4 is low, and TSH is low, normal or slightly elevated, the diagnosis central CH should be considered.
- In neonates with central CH, we recommend to start LT4 treatment only after evidence of intact adrenal function; if coexistent central adrenal insufficiency cannot be ruled out, LT4 treatment must be preceded by glucocorticoid treatment to prevent possible induction of an adrenal crisis.
- In severe forms of central CH (fT4 < 5 pmol/L), we also recommend to start LT4 treatment as soon as possible after birth at doses like in primary CH (at least 10 μg/kg per day, see Section 3.1), to bring fT4 rapidly within the normal range.
- In milder forms of central CH, we suggest starting treatment at a lower LT4 dose (5–10 μg/kg per day) to reduce the risk of overtreatment.
- In newborns with central CH, we recommend monitoring treatment by measuring fT4 and TSH according to the same schedule as for primary CH; serum fT4 should be kept above the mean/median value of the age-specific reference interval; if TSH is low before treatment, subsequent TSH determinations can be omitted.
- The (biochemical) LT4 treatment aim is bringing and keeping the fT4 concentration in the upper half of the age-specific fT4 reference interval.
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