I have been keeping track of 40 mcg Tymlos for over 2 years. You may find this interesting according to @cathyf31's ratio where 150 or better is gaining bone. CTX is divided by 1000. As you can see, all of my blood tests showed over 150, except for 6 months of 40 mcg Tymlos and when I discontinued Tymlos. A half dose of Tymlos worked well for me.

12/23 on 20 mcg Tymlos for one month 78/519=150

5/24 on 40 mcg Tymlos for 3 months 190/1401=136

8/24 on 40 mcg Tymlos for 6 months 310/1414=219

12/24 on 20 mcg Forteo for 3 weeks 190/1238=153

5/25 on 20 mcg Forteo for 6 months 179/912=196

10/25 on 40 mcg Tymlos 5 months since stopped Forteo
and 2 months on 14 mcg Estrogen patch 147/654=224

2/26 on .14 Estrogen patch for 6 months, no Tymlos 38/371=102

I just had my blood drawn again and am waiting for results. I went back on 40 mcg Tymlos for a month and increased my Estrogen patch to 25 mcg for 2 months. I had a very good DEXA a year ago and will be having another DEXA scan next week.