Evaluating the Two-Step TSH Screening Protocol for Congenital Hypothyroidism: Prevalence and Diagnostic Accuracy in...

This study aimed to determine the prevalence of congenital hypothyroidism (CH) among newborns in Ninh Binh Province, Vietnam, and to evaluate whether adding a second thyroid-stimulating hormone (TSH) screening reduces false positives and improves diagnostic accuracy compared with the traditional single-step screening commonly practiced in Vietnam.

A retrospective cohort study was conducted on 11,306 newborns screened between January 2019 and December 2020. TSH levels were measured from dried blood spot samples, with a threshold of >9 mU/L indicating high risk. High-risk cases underwent a second screening, followed by confirmation with serum TSH and free thyroxine. Screening performance (sensitivity, specificity, positive predictive value [PPV], negative predictive value [NPV]) and risk factors for CH were analyzed.

The prevalence of high-risk CH was 2.40% (271/11,306 newborns), with four confirmed cases (incidence: 1:2,826). The two-step screening program achieved a sensitivity of 75.00%, with one false-negative case later detected clinically. Specificity improved from 97.64% in the first screening to 99.81% in the second, while PPV increased more than tenfold (1.11% → 11.54%). Low birth weight infants (≤2,500 g) had a significantly higher CH risk (OR: 10.04, 95% CI: 1.053-95.820, p = 0.004).

This first provincial evaluation of two-step CH screening in Vietnam demonstrated that repeat testing significantly reduced false positives and improved diagnostic accuracy without compromising sensitivity. The findings highlight the value of implementing a two-step strategy to optimize newborn screening, reduce unnecessary referrals and save resources in developing countries.