The authors are indeed fortunate that they have (1) a small case load, (2) serum specimens and not dried blood on filter paper, and (3) the opportunity to measure both thyroxine (T4) and thyroid-stimulating hormone (TSH) in all samples. Unfortunately, in the current economic climate most mass screening programs must limit their laboratory approach to T4 supplemented by TSH measurements or forego the T4 procedure and rely on TSH as the sole marker.

In the latter instance, infants with hypothyroidism secondary to hypothalamic or pituitary disease will be missed and even those with mild primary thyroid insufficiency could be overlooked because of the large coefficient of variation in the assay at TSH concentrations between 20-25 µU/ml in dried blood on filter paper.

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