Neonatal Age and Point of CareTSH Testing in the Monitoring of Iodine Deficiency Disorders: Findings from Western Uganda

Abstract

Iodine deficiency is a major public health problem throughout Africa. Although salt for human consumption is said to contain adequate amounts of iodine in Uganda, iodine intake may not be optimal. We undertook a field study to assess the adequacy of iodine nutrition in western Uganda using on-site measurement methods of neonatal thyroid stimulating hormone (TSH) levels as recommended by the World Health Organization (WHO) for monitoring the degree of iodine deficiency during pregnancy. The study design consisted of a prevalence study using the percentage of newborns between the ages of 3 and 7 days with TSH >5 mIU/L, measured with a point-of-care immunochromatographic TSH assay, as a surrogate marker of iodine deficiency. Five districts in western Uganda were selected for study on the basis of a past history of iodine deficiency. One thousand seventy-eight newborns from the five districts were sequentially enrolled in each separate district and tested between July 2007 and January 2008. The prevalence of TSH levels >5 mlU/L ranged from 20% to 32%. Neonates tested on or before the age of 3 days were more likely to have a TSH level >5 mlU/L than those tested beyond the age of three days (28.2% vs. 18.7%, p < 0.001). Assessing neonatal TSH levels in developing countries with a TSH assay method suitable for field use can be successfully used to screen for congenital hypothyroidism and to indirectly assess a population's iodine status. Based on the percentage of neonates with TSH values >5 mIU/L, presumptive iodine deficiency persists in western Uganda. This finding suggests that continued monitoring of iodine nutrition in the area surrounding the Rwenzori Mountains in Uganda and Congo is needed. Due to the progressive fall in the percent of TSH values >5 mIU/L from day three to day five of life, we conclude that TSH measurement earlier than day five of life in newborns at risk for iodine deficiency may be misleading. Guidelines for the use of neonatal TSH to monitor iodine nutrition should specify that TSH measurement take place no earlier than day five of life.