Pilot study on the adjustment of the cut-off value for congenital hypothyroidism screening according to the age at sampling / 中国新生儿科杂志

ABSTRACT

Objective To study the influence of postnatal age and season of sample collection on congenital hypothyroidism (CH) screening and to determine the appropriate cut-off value. Method From January 2015 to December 2017, neonatal thyroid stimulating hormone (TSH) screening data in Guangzhou were retrospectively analysed. The infants were assigned into four groups according to sampling postnatal age24～＜48 h, 48～＜72 h, 3～＜7＜d and≥7 d, and assigned into another four groups according to their birth seasons. Based on the data of 2015 and 2016, the cut-off value of TSH for hypothyroidism were adjusted. The data of 2017 were used to verify the accuracy of the adjusted cut-off value. The cut-off value was determined based on the receiver operating characteristic (ROC) curve and percentile method. Specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) of the cut-off value were also calculated. Result A total of 459854 newborns were screened from 2015 to 2016. 7329 were positive in preliminary screening, 371 were still positive after recall for re-examination, and 318 were confirmed with CH eventually. The optimal TSH cut-off value calculated using ROC curve was 9 mIU/L, with a percentage of 98.7. The cut-off value with sampling time≥48 h was set to 9 mIU/L in spring, summer and autumn, and 10 mIU/L in winter. The cut-off of sampling time 24～＜48 h was set to 10 mIU/L in all seasons. The data of 264993 newborns screened in 2017 were verified using the adjusted cut-off value. The overall positive rate was reduced from 1.27％to 1.02％, and the PPV was increased from 6.07％to 7.58％without adding false negative cases. Conclusion Adjusting cut-off values of TSH for CH screening according to postnatal age and season can effectively reduce false positive rates.