The classical inherited metabolic disorders, or inborn errors of metabolism, are enzyme defects in the metabolism or breakdown of amino acids (protein building blocks), carbohydrates or complex sugars, fatty acids, or mitochondrial energy production. Many of them are readily diagnosed with basic blood and urine metabolic testing looking for the accumulation or depletion of various compounds surrounding the enzyme block. These studies include lactate and pyruvate levels, ammonia, plasma and urine amino acids, urine organic acids, carnitine and acylcarnitine profiles. Other inborn errors require more complex and sometimes more invasive testing such as specific DNA gene testing or muscle biopsy for myopathies including mitochondrial disorders. In general, they all require the expertise of a metabolic specialist to put all the pieces of the puzzle together into a recognizable picture.