In Reply.—It was precisely because of the arguments cited by Dr Banagale that my co-workers and I chose to study healthy, term infants at 2 to 3 weeks of age. Analysis of thyroid hormones in breast milk is beset with many problems; premature infants frequently have low serum T4 values. Finally, any effect of nursing should be more evident after nursing is well established.
The results of recent studies performed by my colleagues and me in collaboration with the Texas Department of Health, support Dr Banagale's contention that the method of feeding does not impair the accuracy of neonatal screening programs for primary congenital hypothyroidism. The mean filter paper spot-test T4 value of breast-fed infants is marginally higher than that of formula-fed infants, aged 2 to 3 weeks old. However, the overlap of values is so great that the difference is not clinically important. Therefore, we conclude