How do you test and monitor propionic acid levels?

Although there are tests available that can measure propionic acid levels in the bloodstream and urine, there are no set standards that we can use to determine if a level is too high or low. Furthermore, there are various metabolic variants of propionic acid (3HHA, 3HPA, HPHPA) that may actually be able to be used as a marker for autism. From a practical standpoint, if a child under my care has any features resembling autism, any spectral disorder, ADD/ADHD, a mood disorder, or any form of developmental delay, I am going to initiate this simple and safe protocol because any of these diagnoses has a good chance of recovering regardless of the result of a propionic related test result.