RESUMO
INTRODUCTION: The metabolic screening test gives the first laboratory indication for neurometabolic alterations which can cause mental retardation. Some techniques such as thin layer chromatography, are still used in several countries to confirm the diagnosis of inborn errors of metabolism after a general screening test. PATIENTS AND METHODS: Two patients from a mentally retarded Colombian population were reported positive for the Nitrosonaphtol test, and remained positive to tyrosine metabolism alteration by thin layer chromatography, suggesting the correspondent management. In the present study we tried to confirm the last diagnosis, performing tandem mass spectrometry analysis of acylcarnitines and amino acids, on blood samples of all patients from the last study, which were found negative for any alteration. CONCLUSION: Is necessary to improve the diagnosis methods used in some countries in order to avoid mistakes that can change the life-style of the wrongly diagnosed patients.