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

OBJECTIVES

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.

METHODOLOGY: 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.

RESULTS

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).

CONCLUSIONS

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.