PURSUING OBJECTIVE PERFORMANCE METRICS OF NEWBORN SCREENING (NBS) TESTS FOR LYSOSOMAL STORAGE DISORDERS (LSD) Matern D 1 , Orsini J 2 , Bentz Pino G 1 , Tortorelli S 1 , Oglesbee D 1 , Gavrilov D 1 , Rinaldo P 1 , Raymond K 1 1 Mayo Clinic College of Medicine, Rochester, MN, United States 2 New York Department of Health, Albany, NY, United States NBS for one or more LSD has been implemented in New York, Illinois, and Taiwan by enzyme assay using either MS/MS or fluorometry. Other assays have also been proposed. To prevent a recurrence of the significant variability in NBS performance that characterized the application of MS/ MS in NBS, a web site has been created to provide reference and disease ranges for all assays considered for LSD screening (www.nbstrn.org). Similar to the worldwide MS/MS collaborative project (McHugh DMS et al. Genet Med 2011; 13:230-54) , the goal is to collect assay-specific data sets of at least 50 true positive cases per LSD to establish disease ranges that will allow provision of cutoffs resulting in optimal analytical performance (high sensitivity and positive predictive value, low false positive rate). To achieve this goal, participation by screening laboratories and LSD specialists is crucial. All participants will have access to pages unique to their regional NBS program for data submission and comparison tools and to common pages inclusive of project tools and reports. LSD specialists are encouraged to facilitate the retrieval of any residual NBS samples of their patients. Background: Early detection of inborn metabolic disorders (IMD) by tandem mass spectrometry (MS/MS) enables early diagnosis and treatment to minimize morbidity and mortality. Objectives: To evaluate expanded newborn screening (ENS) results retrospectively and to identify the incidence of IMD in Turkey with our laboratory's data. Material and Methods: 107463 neonates were screened for IMD by tandem MS/MS from 2002 to 2010. Blood spots were collected between 2nd-7th days after birth. Acylcarnitine and aminoacid concentrations were determined by using tandem MS/MS. Further diagnostic tests were performed on newborns with elevated screening results by metabolic diseases centers and our laboratory. Results: We detected a total of 170 patients with IMD; 87 patients with aminoacid metabolism defects, 26 patients with fatty acid oxidation defects and 57 patients with organic acidemia. The overall incidence of these diseases was 1:632. Defects in aminoacid metabolism were the most common disorders. Conclusion: Our study showed that the incidence of IMD detected by ENS is very high in Turkey. The distribution of patients according to years revealed an increased incidence at recent years. This finding may be explained with the more widespread use of the ENS by tandem MS/MS. Background: Many Steps, much more links and mass data make it difficult to be operated and to manage its data in neonatal screening.