The best test currently available for EPM requires the collection of a cerebrospinal fluid (CSF). This fluid is tested for the presence of antibodies against Sarcocystis neurona. The test should be pursued only in horses with neurologic signs, not as a screening test in horses without signs of EPM. The test is called the western immunoblot, which detects antibodies produced against the organism in the central nervous system. Blood contamination of the CSF fluid sample will cause a false positive test in horses with a positive blood titer, and therefore should be interpreted with caution.
for more information, please read the article Equine Protozoal Myeloencephalitis