medwireNews: Congenital hypothyroidism (CH) of central origin (CHC) should not be dismissed as a mild condition and is worth screening for, say researchers.

Nitash Zwaveling-Soonawala (Academic Medical Center, Amsterdam, the Netherlands) and team analysed data from neonatal screening using free T4, thyroid-stimulating hormone (TSH) and T4-binding-globulin (TBG).

They found that 2.8% of children with CHC had severe disease (free T4 <5 pmol/L) and 52.4% had moderate disease (5 to <10 pmol/L), requiring immediate thyroxine replacement.

CHC is considered a milder condition than CH of thyroid origin (CHT), and indeed more children with the latter condition had severe disease, at 26.5%, with 32.3% having moderate disease.

However, the team says: “The clinical relevance of moderate CH is not questioned and the ESPE consensus guidelines for CH advise that treatment with thyroxine should be started immediately when [free T4] values are below norms for age to prevent brain damage due to thyroid hormone deficiency.”

A similar proportion of CHC and CHT children had mild disease (free T4 ≥10 pmol/L), at 44.8% and41.2%, respectively.

“This is a strong argument for adapting existing neonatal CH screening programs in a way that detection of both CHT and CHC is possible”, write the researchers in the Journal of Clinical Endocrinology & Metabolism.

The study data arise from 143 children with CHC and 1057 with CHT, who were identified through the Dutch CH screening programme. The programme measures T4, in addition to TSH, allowing detection of both CHT and CHC.

Most screening programmes are based solely on TSH, and effectively detect only CHT, says the team.

The Dutch programme employs a stepwise approach, with T4 measured initially and TSH measured only in children in the lowest 20% of T4 values, thus avoiding the detection of children with elevated TSH levels in the context of normal T4 values. Zwaveling-Soonawala and team say this finding is of questionable clinical significance, and places an unnecessary burden on families.

The programme also incorporates TBG measurement, to allow calculation of the ratio of T4 to TBG, thereby excluding false–positive CH cases caused by “harmless” TBG deficiency.

“This approach has proven to be very effective in detecting CHC with a rise in detection rate of permanent CHC in the Netherlands from 1:25,000 to 1:16,000”, say the researchers.

However, they concede that adding TSH and TBG measurement to a screening programme comes at extra cost.

By Eleanor McDermid, Senior medwireNews Reporter

J Clin Endocrinol Metab 2014; Advance online publication

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