ESPE Abstracts

We present the case of a five-day female admitted to our Paediatric Unit due to TSH elevation (bTSH 303 mIU/L) on routine neonatal screening for congenital hypothyroidism (CH). The patient was born at 38 weeks’ gestation by c-section presenting with adequate auxological parameters. Her mother suffered from Hashimoto’s disease, already diagnosed before pregnancy, and requiring Levo-thyroxine therapy (L-T4). Blood tests performed at five days of life revealed the presence of an important TSH elevation (TSH 400 mIU/L) with FT4 values above the normal limit for age (fT4 2.61 ng/dL) and negative thyroid antibodies; the ultrasound showed an in-situ gland, with normal echotexture. Because of the discordant thyroid function test results, blood tests were repeated also evaluating the potential presence of immunoassay interferences. In particular, the detection of Polyethylene Glycol (PEG) thyrotropin precipitable percentage was performed, confirming the presence of monomeric TSH complex with autoimmune anti-TSH antibodies, mostly IgG, interfering with the immunoassay analytic procedure, which resulted into fictitiously elevated TSH values (macro-TSH) both in the patient and her mother, not previously referred. TSH measured after PEG precipitation was 36.2 mIU/L equal to 9% of total TSH (400 mIU/L), with normal fT4 and fT3 (respectively, 2.14 ng/dL and 3.30 pg/mL). Thyroid function reassessed after one week confirmed the persistence of macro-TSH (399 mIU/L) and increased TSH after PEG precipitation assay (44 mIU/L, 11% of total TSH). Hence L-T4 therapy was started at the dosage of 7,34 mcg/kg/day at thirteen days of life. Periodic blood tests showed a progressive improvement of TSH values leading to adjustment in L-T4 therapy. Macro-TSH interference at immunoassay assessment persisted, with a significant decrease of non-precipitable percentage (from 91% to 75% at 30 days after starting treatment). This case suggests that, albeit rare, possible immunoassays interferences should be considered in presence of high serum TSH levels and inappropriately normal FT4 values before starting L-T4 therapy in a newborn suspected of CH. A careful maternal anamnestic data collection is of fundamental importance and in suspected cases mothers’ macro-TSH should be controlled as well. The progressive reduction of the non-precipitable percentage during the follow-up suggests a possible transient condition, due to the IgG composition of the immunocomplexes responsible for the phenomenon, which could be easily derived from a trans-placental transmission. The child thyroid function will be revaluated after the age of two according to international guidelines.