Background: Tandem mass spectrometry (TMS)-based newborn screening has been proven successful as one of the public healthcare programs, although the practicability has not yet been specifically addressed. Methods: Sixty residual dried blood spot (DBS) specimens from confirmation/diagnosis-insufficient cases discovered by TMS screening were analyzed by targeted next generation sequencing (TNGS) assay. Results: In total, 26, 11, 9, and 14 cases were diagnosed as positive, high risk, low risk, and negative, respectively. Conclusions: Applying the DBS-based TNGS assay for the accurate and rapid diagnosis of inborn errors of metabolism (IEMs) is feasible, competent, and advantageous, enabling a simplified TMS screening-based, TNGS assay-integrated newborn screening scheme highlighting an efficient, executable, and one-step screening-to-diagnosis workflow.