Methylmalonic acidemia can be detected by checking the urine. Urinary methylmalonic acid is much higher than normal in patients with methylmalonic acidemia. Methylmalonic acidemia can be detected by general examination, blood acylcarnitine detection by tandem mass spectrometry, urine organic acid detection by gas chromatography-mass spectrometry and enzymatic analysis. 1. General examination: routine biochemical examination includes routine blood and urine, liver function, renal function, blood gas analysis, blood glucose, electrolytes, blood ammonia, blood lactic acid, serum homocysteine and so on. Urine methylmalonic acid and its metabolite 3-hydroxypropionic acid, methyl citrate and other organic acids are significantly increased. 2. Tandem mass spectrometry for blood acylcarnitine: Determination of free carnitine, acetylcarnitine and propionylcarnitine in blood. In children, the level of propionylcarnitine and the ratio of propionylcarnitine to acetylcarnitine in blood are elevated. 3. Detection of urinary organic acids by gas chromatography-mass spectrometry: urinary excretion of methylmalonic acid, methylcitric acid and 3-hydroxypropionic acid increased significantly. 4. Enzymatic analysis: Determine the type of enzyme deficiency in children with methylmalonic acidemia by testing the enzyme activity of skin fibroblasts and peripheral blood lymphocytes. Patients with methylmalonic acidemia should go to the hospital for timely examination and treatment under the guidance of a doctor.