Newborn screening for congenital hypothyroidism: improved assay performance has created an evidence gap

Excerpt

The introduction of newborn screening for phenylketonuria in the 1960s provoked considerable controversy. By contrast, once reliable assays for thyroid hormones in dried blood spot samples had been developed in the mid-1970s, there was ready acceptance of routine screening for congenital hypothyroidism (CHT). This was a well-recognised clinical condition, albeit with varied aetiologies, and prompt treatment rapidly reversed many of the symptoms. Worldwide, some 12 million babies a year are now screened for CHT in programmes that are generally regarded as highly successful. As described in the accompanying review (LaFranchi 2010), a variety of screening protocols are in use, the choice being influenced partly by the age at which the screening blood sample is taken. From the outset, screening has tended to detect more cases than anticipated on the basis of previous clinical experience (references in LaFranchi 2010). As assay sensitivity improved some screening programmes, particularly those using a primary thyrotropin (TSH) test strategy, responded over the years by adopting lower cut-offs, with a further increase in apparent incidence. The status of such ‘additional’ babies and the optimum balance between screening sensitivity and specificity are still matters of debate. …