Inborn errors of metabolism (IEM) are rare genetic (inherited) disorders comprising hundreds of diseases. The signs and symptoms of IEMs can mimic almost any pediatric disease. The symptoms may be similar to infectious diseases such as lethargy, not suckling, vomiting, convulsions, panting, etc. Therefore, it is difficult for non-specialist physicians to detect the disorders resulting in delayed diagnosis and treatment which may further lead to mental retardation, permanent disabilities, or death during infancy or childhood. Currently, there is a technology called Tandem Mass Spectrometry (MS/MS) that can detect more than 40 IEMs in a single blood spot. MS/MS is therefore being used for screening and diagnosis of IEMs in newborns and sick infants in many countries. In 2013, an economic study to evaluate value for money of expanded newborn screening for 6 IEMs with MS/MS was performed. At that time, it was found that such screening was not worthwhile. But now the situation has changed, such as the willingness to pay threshold for Thailand, the number of IEMs that can be screened, cost of medical care and quality of life of patients, etc., thus leading to a recent study on economic evaluation and feasibility assessment of expanded newborn screening for IEMs using MS/MS technology. There are four specific objectives of this study: 1) to assess cost utility of the expanded newborn screening using MS/MS (cost-utility analysis) and treatment of patients with IEMs; 2) to study the cost of illness (cost-of-illness) of IEM patients 3) To analyze budget impact of expanded newborn screening and treatment of IEM patients and 4) To study feasibility of including expanded newborn screening using MS/MS for all Thai newborns in the benefit package of the Universal Coverage Scheme. The study used a combination between Decision tree analysis model for simulation of screening scenarios and the Markov model for simulating the health status of IEM patients. A total of 41 IEMs that can be screened by MS/MS were included. The study estimates costs and outcomes in terms of life year and Quality-Adjusted Life-Year (QALY), reported as incremental cost-effectiveness ratio: ICER in baht per QALY gained, comparing the situation between providing expanded newborn screening and current situation without expanded newborn screening. A comparison of the outcome and cost of treatment before and after clinical presentations were also analyzed to illustrate the potential benefit of early treatment for affected children. A lifetime time horizon and societal perspective were applied. For budget impact analysis, provider’s perspective was used. In addition, the study employed survey and in-depth interviews with key stakeholders to explore the feasibility and current capacity of proving expanded newborn screening. The study found that providing early treatment before clinical manifestation is cost effective compared to providing late treatment. The ICER was between dominant ICER to 120,995 THB per QALY gained, depending on the disease groups and its complications, except for Tyrosinemia Type I, with an ICER of 1,073,540 THB per QALY gained. The ICER of expanded newborn screening using MS/MS ranged between 259,824 – 576,711 THB per QALY gained depending on cost of screening and incidence of IEMs. The cost of illness for a patient is as high as 3.6 million up to 8.7 million THB because the patient needs a lifelong treatment by medical professionals. The additional budget for screening and treating patients in the first year is at 30 million THB. The total budget for 5 years is 283 million THB. Currently, there are 2 MS/MS providing services in Thailand that can serve up to about 60,000 patients per year. In order to cover all newborn nationwide, 14 MS/MS should be put in place. Therefore, 12 MS/MS is still needed and trainings for staff should be also provided. Policy recommendations 1. NHSO should consider including expanded newborn screening with MS/MS technology as a benefit package under the Universal Coverage Scheme. Although the expanded newborn screening was not cost-effective, it is the only accurate method of early detection and providing pre-clinical treatment that improves health outcomes and prevents complications leading to permanent disabilities. Providing early treatment was cost effective. In addition, IEMs cause huge economic burden to patients and their relatives and were regarded as a catastrophic illness. Furthermore, treatment for IEMs is already covered by the UCS, but identify potential patients for treatment remains a major obstacle that prevents these patients from accessing the services. 2. Recommend NHSO to 2.1 Negotiate the price of screening that the government can afford with the participation of responsible government agencies and service providers. If the expanded newborn screening is operated throughout the country, the cost of supplies from private firms may be negotiated. 2.2 Collect information about screening service utilization, incidence of IEM, following-up for diagnosis, as well as problems and obstacles for further development and expansion of the program 2.3 Assign the rare disease working group under UCS to develop an action plan for providing expanded newborn screening in order to achieve universal service access as quickly as possible. This will include establishing guidelines for registration of rare disease screening centers, guidelines for providing screening services and information systems (software) and adding representatives from the Ministry of Social Development and Human Security, Thailand (PMO) to join the rare disease working group. 2.4 Coordinate with the Food and Drug Administration to speed up the registration process of drugs and metabolic formula for the treatment of IEM patients. 3 . Relevant agencies should discuss and establish an effective system to deliver blood specimen to the MS/MS Screening Center within 24 hours. 4. A National Newborn Screening Advisory Committee should be established to provide advices and recommendations on the integration of Thailand's newborn screening system, newborn screening database, accreditation of newborn screening centers, and monitoring and evaluation of newborn screening in the country.