Determining the Reference Range of Amino Acids in Healthy Neonatal Blood Samples in Northeast Iran Using LC-MS/MS.

Background: Amino acid analysis is an important tool for the diagnosis of metabolic disorders in newborns. Today, Liquid Chromatography tandem mass spectrometry (LC-MS/MS) has emerged as a powerful technique for amino acid analysis. We aimed to determine the local normal range of amino acids in dried blood spot (DBS) samples of neonates using LC-MS/MS.

Methods: A total of 1005 samples from healthy neonates of northeast and east of Iran aged 2-7 days were utilized for normal range determination. The amino acids were extracted from dried blood spot samples using organic solvent and then analyzed using LC-MS/MS system. The 1%, 2.5%, 97.5%, and 99% percentiles were calculated, and the results were compared to the global cut-off values.

Results: The results showed that glutamic acid has the highest concentration range among amino acids evaluated in this study (178.94 - 421.31µmol/L). Moreover, the plasma concentrations of Glycine (142.65 - 397.06 µmol/L), Alanine (97.00-349.72 µmol/L), Proline (63.77 - 236.53 µmol/L), and Tyrosine (25.79 - 150.58 µmol/L) were in the next ranks. Comparing the obtained results with the global values obtained in the R4S study indicated a slight difference between the obtained local normal values and the global values.

Conclusions: The calculated values were slightly different from global values obtained in the R4S study and regional values calculated in other studies. This further emphasized the importance of the local establishment of reference values, which facilitates the correct interpretation and diagnosis in the Newborn Screening Programs.