@gently I had some gain from Forteo, but only in my spine, going from -3.8 to -3.5, a 4.6% increase. My left total hip and left femoral neck were unchanged, at -2.2 and -2.6, respectively.
My TBS score is 1.223, which is degraded microarchitecture, same as before.
My former rheum did not use BTMs to guide clinical treatment, which as I'm sure you know is not uncommon. I ordered and paid for them myself before starting on Forteo. CTX was 100; P1NP was 13. This was after 3.5 years on Fosamax.
Three months after starting Forteo, I had BTMs done again. CTX now 431 and P1NP 64. Since my rheum offered no interpretation, I relied on Dr. AI, which said "increased CTX is normal in the early stages of treatment with teriparatide. A higher CTX number after 3 months on teriparatide is expected because this medication primarily stimulates bone formation, which initially leads to a temporary increase in bone resorption (as measured by CTX) as the body starts the remodeling process to build new bone, even though the net effect is a gain in bone density over time; essentially, teriparatide "primes" the bone to rebuild itself by increasing bone turnover, resulting in a higher CTX level early in treatment. When monitoring P1NP levels while on Forteo (teriparatide), a significant increase of more than 10 µg/L from your baseline level after 3 months is generally considered a positive response, indicating that the medication is effectively stimulating new bone formation; this is often used as a benchmark to assess treatment efficacy. " So it seemed to me the Forteo was working.
I had no other BTMs and my DEXA on 3-12-26 was my first one since 3-11-24. (My very first DEXA on 10/27/2020 had my femoral necks at -2.3 and lumbar spine at -3.8, at which point I went on Fosamax. I might have quit Fosamax sooner had I had a DEXA two years later in 2022 but my PCP--I wasn't seeing a rheum at that time--never suggested it and I didn't know any better.)
I too wondered about underlying causes such as hyperparathyroidism for which I was tested prior to starting Forteo. Normal.
I am hopeful my new rheum, who I can't see until late May, uses bone markers and will agree with me about another, different round of anabolic, i.e. Evenity.