Diagnostic Utility of Cord Blood Thyroid Stimulating Hormone in Congenital Hypothyroidism in the Era of Expanded Newborn Screening

Even in the era of expanded newborn screening, utility of cord blood thyroid stimulating hormone (cTSH) for diagnosis of congenital hypothyroidism (CH) cannot be marginalised. This study was to assess the diagnostic utility of cTSH > 20 μIU/L for screening CH. Generation of new cTSH value was the main outcome measure, to increase specificity. Designed as a cross-sectional analytic study in the neonatal unit of teaching hospital, 1200 term neonates with birth weight ≥2500 g, with no perinatal complications were included. Newborn cTSH assay was done by chemi-luminescence. All screen positive were followed up on day five, 14 and 28 of life, to rule in or out CH (true or false positive). Positive predictive value and specificity were calculated. Receiver operating characteristic (ROC) was done to assess diagnostic accuracy of cTSH > 20 μIU/L and to ascertain new cut-off to reduce false positivity. Of 1200 newborns screened, 69 (5.8%) were screen positive and followed up. In five, CH was confirmed (true positive); one in 240 newborns required thyroxine therapy. False positivity was noted in 59. Recall and dropouts were 6.25 and 7.2% respectively. Median cTSH of screen, true and false positives were 28.8, 43.5 and 27.2 μIU/L respectively. Comparison of median values of cord blood (U = 59; p = 0.017) and day five serum TSH (U = 0.0; p < 0.001) among true and false positive subjects were statistically significant. Specificity calculated was 94.6% and positive predictive value 7.25%. ROC generated new permissible cTSH cut-off value of 30 μIU/L. In conclusion, an extended cTSH cut-off value of 30 μIU/L improves specificity.