@ddljohn-- My sister had this done. It took her six weeks to get the results. The equipment needed to test spinal fluid isn't available at every lab, so don't be surprised if it takes a long time.
What they look for in the cerebrospinal fluid for diagnosis of autoimmune disorders, is antibodies. The same is true when there is an infection. When the body is fighting off infections, or fighting its own tissues due to an immune system disorder, it releases antibodies in the cerebrospinal fluid. They might look for some other substances as well, but I'm not sure what all of them are.