How can we interpret metabolic tests

introduction: There are some laboratory methods that can help diagnose metabolic diseases, the following are some examples: 1) HPLC (High Performance Liquid Chromatography): This method is a quantitative analysis of amino acids. For the diagnosis of most amino acid disorders, morning fasting blood specimens are required. Some of the important aminoacidopathies that are diagnosed or suspected by this method include: MSUD , UCD , PKU , Hyperglycinemia, Tyrosinemia, Homocystinuria and … 2) Tandem mass spectrometry (MS/MS ): An analytical method on DBS that uses two mass analyses. This method performs the analysis of some amino acids and acylcarnitine profile. So, it can help in the diagnosis of some aminoacidopathies, such as MSUD, PKU, Tyrosinemia. On the other hand, this method is very important in diagnosis of FAOD . Some of these important compounds and related diseases include: a) ↑ C4 (Butyrylcarnitine): SCAD D b) ↑ C8 (Octanoylcarnitine): MCAD D c) ↑ C4OH (Hydroxybutyrylcarnitine): SCHAD D d) ↑ C14: 1 (Tetradecenoylcarnitine): VLCAD D e) ↑ C16 (Hexadecanoylcarnitine): CPTII D But MS/MS is only a suggestive method for organic acidemia (OA), such as: 1) ↑ C3 (Propionylcarnitine): PA - MMA and MCD . 2) ↑ C5 (Isovalerylcarnitine): Isovaleric acidemia. 3) ↑ C5OH (3-hydroxyisovalerylcarnitine): Suggestive for MCC - MCD - HMGL and BKT So, analysis of urine organic acids by GCMS is necessary for final diagnosis of OA. 3) Urine GCMS: This method is generally performed by capillary gas- liquid chromatography/mass spectrometry on an untimed random urine sample. It is important that a definitive diagnosis can only be reached after repeated quantitative urinary organic acid analyses, especially during metabolic decompensations. Elevation of some important metabolites in a urine organic acid analysis, are emphasized at below: 1) 3-hydroxypropionic acid: in PA- MMA- biotin disorders- 3hydroxyisobutyric aciduria. 2) 3-hydroxyisovaleric acid: in all leucine degradation defects- biotin disorders- ketosis 3) Methylmalonic acid: in MMA- malonic aciduria 4) Isovalerylglycine: IA - biotin disorders- GAII 5) N-acetyltyrosine: tyrosinemia (all forms) 6) Succinylacetone: tyrosinemia (hepatorenal form only) 7) Methylcitric acid: PA- MMA- biotin disorders 8) Orotic acid: UCD - orotic aciduria.