No.

1. You may be positive for MuSK antibodies.
2. You may be positive for LEMS antibodies.
3. You may be positive for antibodies that are known, but for which a standard test doesn't yet exist (LRP4 and others).
4. You may be positive for antibodies that haven't been discovered yet.
5. You may have AChR antibodies that didn't show up on the test (this is quite common, especially early in the disease). Your doctor should test you again in a few months.

If someone tests negative for AChR, MuSK and LEMS antibodies, MG can still be diagnosed. The diagnosis might be:
1. Clinical (based on symptoms)
2. Based on a tensilon test (a shot of a fast-acting drug)
3. (Most common, I think) Based on a SFEMG (single-fiber EMG)
4. Based on the patient's response to Mestinon, which (like Tensilon) inhibits the enzymes that break down acetylcholine, the chemical that the nerves use to communicate with the muscles.

Abby