I stopped Tymlos in January, and started Fosamax. My doctor said I could get a blood test for P1NP/CTX any time within six months, so I'll be doing so next week at the four-month mark, mostly to satisfy myself. At one year, I will repeat the tests and get a DEXA. I have three years' worth of bone markers now, both pre-Tymlos and during treatment, so I have a good history to evaluate any new results.