Until a true biomarker is identified, a 2 day CPET is the best way to “prove” ME by measuring anaerobic threshold and post-exertional malaise (PEM). This test is only offered in three US locations that I’m aware of, in NC, CA and NY (Ithaca). The test should be considered carefully, as it can cause significant crashes or setbacks. Health Rising article. It has been useful in applications for SSDI. Here’s a great article on the work that Besty Keller is doing with this at Ithaca College: Tireless Work on Chronic Fatigue Syndrome.