False-negative primary neonatal thyroid screening: the need for clinical vigilance and secondary screening.

The screening of newborn babies for congenital hypothyroidism has changed the natural history of this abnormality. We describe here a case of a female patient with congenital hypothyroidism that was missed by primary neonatal thyroid screening (using thyroid-stimulating hormone) at two days of age; it was detected only after the development and persistence of jaundice during the first three weeks of life. A normal neonatal screening result does not preclude the development of hypothyroidism later in infancy. Clinical vigilance must be maintained by practitioners. A second screening between two and six weeks of age may be useful in order to detect the few cases missed at first screening.