1.Low T4, high TSH: About 80%-90% are primary hypothyroidism, a few are temporary hypothyroidism. 2, low T4, normal TSH: seen in preterm infants, low T3 syndrome, TBG deficiency, secondary hypothyroidism or primary hypothyroidism with delayed elevation of TSH. TRH excitation test can identify pituitary TSH deficiency if the TSH response level is low, or hypothalamic TRH deficiency if the TSH response peak is normal. TSH in children with primary hypothyroidism may rise to a level sufficient to diagnose hypothyroidism only a few weeks after birth and should be repeated. 3. Normal T4, high TSH: Normal T4, or at the low limit of normal, and a persistently high TSH indicates insufficient T4 production. This group of children should be repeated and have a thyroid scan.