This can be done by any lab. I know that it has to be mailed fairly fast afterwards. Mayo's test results come back showing ranges for minrmal, low, and deficient enzyme levels. Each deficient level is tied to an hereditary porphyria type. The key to toxic induced porphyria is the variation in enzyme level and multiple enzyme variation.
Diagnosis requires the deficient levels plus symptoms.
Hope that helps. Defining Multiple Chemical Sensitivity is a carefully documented story written to factually and scientifically correct some of the misinformation about MCSS and her own case. The first chapters cover some of the latest work in biomarkers for demonstrating chemical poisoning. These papers go a long way towards providing an understanding of why the chemically poisoned experience such brain fog and react to so many things. And these are the same amino acids which are implicated in brain cell injury - stroke, pain, depression and degenerative brain disease.