Neonatal thyrotropin profile as an index for severity of iodine deficiency and surveillance of iodine prophylactic program

Abstract

Neonatal serum thyrotropin (TSH) level has been proposed as an index for the monitoring and surveillance of an iodine prophylactic program. We have determined an effective way to put this idea into practice. During the first phase of our study, neonatal serum TSH levels were obtained from umbilical cord blood of neonates born in Chiangmai and Nan provinces, where several districts were areas of severe iodine deficiency, and were compared with those of neonates born in Bangkok, which was a control area. The median and (95% CI [confidence interval]) of serum TSH level of neonates born in Chiangmai 5.8 (5.7-5.9) μU/mL was significantly higher than in Nan 5.1 (5.0- 5.2) μU/mL, and in Bangkok 3.7 (3.7-3.8) μU/mL. Neonatal serum free thyroxine (FT4) concentration in Bangkok was higher than in Nan, while the reciprocal was true for neonatal TSH concentration in randomly selected samples (FT41.6 [1.6-1.7] ng/dL rs. 1.5 [1.5-1.6] ng/dL and TSH 3.5 [3.3- 3.9] μU/mL vs. 5.5 [5.2-5.9] μU/mL, respectively.) When odds ratio of the likelihood of having neonatal TSH level higher than in Bangkok was calculated using 95th percentlie value of neonatal TSH level in Bangkok as a cut-off point, the odds ratio of TSH profile in all districts in Chiangmai and Nan were greater than unity. In the second phase of our study, data were collected from 32 district and 10 provincial hospitals. The optimum number of samples in each hospital derived from the first phase of our study was at least 178. Discrepancy between goiter rate and odds ratio of TSH profile was observed, but there was a significant correlation between the two indices (r = 0.67, p < .001). Our study confirmed the practical utility of neonatal TSH profile as a biological index for assessment and monitoring and surveillance of an iodine prophylactic program at a district hospital in a developing country.