Evaluation of sensitivity and specificity of filter paper inscreening of congenital hypothyroidism

Congenital hypothyroidism (CH) is one of the most preventable causes of mental retardation throughout the world. The aim of this study was to evaluate the sensitivity and specificity of filter paper in screening for congenital hypothyroidism and to determine an appropriate cut-off point for filter TSH for recalling screened neonates.

In this cross-sectional study (descriptive analytic), the records of 2739 neonates who had been recalled during the CH screening program in the east of Tehran, Iran (health care centers of the Iran University of Medical Sciences), from March 2011 to March 2015, were studied. According to the CH screening program in Iran, the TSH on filter paper>5 is the current cut-off point for recalling the neonates. The data was analyzed with SPSS software, version 21. The ROC curve was used to determine the TSH cut-off point and the sensitivity and specificity of the filter test. The relationship between the filter and serum TSH was also determined. The study was approved by the Ethics Committee of the Iran University of Medical Sciences.

The recall rate was 5.4%. The prevalence of hypothyroidism was 3/1000 neonates (164). The prevalence in males and females was 51.1% and 48.9%, respectively, with no significant difference. The number of recalled neonates diagnosed as patients with congenital hypothyroidism based on the filter TSH level was 5<TSH≤10(71), 10<TSH≤20(39), 20<TSH(54). There was no significant difference in seasonal prevalence of hypothyroidism or mean TSH level on filter paper among the four seasons. There was a moderately significant relationship between serum and filter paper TSH levels (r=0.379, P<0.05). Based on the ROC curve, the cut-off point for recall of 6.5 mIU/L with a sensitivity 77.5(0.771-0.777) and specificity          58%(0.575-0.585) and an area under the ROC curve of 0.74 was obtained.

Based on the findings of the study, considering the kits available in the country and their sensitivity and specificity, the importance of diagnosing infants with congenital hypothyroidism, and the lower cost of filter paper than missing a hypothyroid infant, the current cut-off point is acceptable. However, more studies are needed in different regions of Iran to obtain more accurate results.