Is there such a thing as a bulimia test?

My step-daughter lost a lot of weight fast and started looking sickly thin. I asked her about bulimia and she diverted the question with the reply that "my mom took me to the doctor and had me tested for it and it was negative." I have never heard of a bulimia test. She said it was either blood or urine I forget which, not a Q and A test in other words. Actual lab work was done. What was the doctor looking for and is there really such a thing? I felt like she never answered my question and so I had considered if there was a test for it and she was negative, it was possible that she was engaging in some bulimic behaviors but not enough to trigger a chemical response in her body. However, enough for her to look sick and be rail thin. anyone know about this? I've googled the subject with no luck.