I have a Medicare Advantage Plan which has so far covered the CTX and P1NP tests ordered. The first time the P1NP came back quickly but the second time it took weeks. possibly due to some shortage of supplies.

McCormick and some doctors want a baseline for both. They should be done fasting (or at least CTX should be) and at the same time relatively early in the morning.

My understanding is that CTX measures bone turnover and is helpful in assessing anti-resorptives and P1NP measures bone formation and is helpful with anabolics along with the CTX. But I refer folks to McCormick's book "Great Bones" for more explanation. I am still on Tymlos at the recommendation of docs and McCormick, despite my blood tests looking like it is no longer working. It is maintaining me until Evenity on 12/21.

For CTX: https://healthresearchfunding.org/ctx-blood-test-results-meaning/ (randomly chosen source)
"For people who are not taking any medication for their osteoporosis, then a higher than normal level of CTx can indicate that there is a higher risk of bone fractures occurring.

For those who are just starting medication for osteoporosis, then if a 35% minimum drop in CTx numbers is achieved within the first 90 days of therapy, it is an indicator that the drug is working and will likely improve long term expectations. In some individuals, a 55% drop in CTx numbers have been documented. Improvements below 35% may also indicate progress, but require adjustment to the treatment plan.

For people who are already taking osteoporosis medications and have been doing so for some time, the CTx blood test may not be helpful. The exception here is if an oral surgery is being considered. The test can help to determine the risks of side effects that are related to the jaw bone from drugs that may be administered during the procedure."

PiNP https://www.labcorp.com/tests/140850/intact-n-terminal-propeptide-of-type-1-procollagen
"The International Osteoporosis Foundation (IOF) and International Federation of Clinical Chemistry (IFCC) has recommended serum P1NP as bone formation for use in fracture risk prediction and monitoring of osteoporosis treatment.7 The National Bone Health Alliance, working in association with the American Association for Clinical Chemistry, established that the preferred bone formation marker is P1NP in clinical studies of bone turnover.8 The application of P1NP as a biomarker of bone turnover in various clinical applications has been reviewed extensively.9-13 The P1NP assay provides a sensitive tool for assessing increased bone turnover in postmenopausal women.14-19 Unlike bone density measurements, P1NP levels can show appreciable, rapid response to changes in turnover rate, supporting its clinically use for monitoring treatment response and adherence in osteoporotic patients from the onset of treatment initiation.13 P1NP has been applied for monitoring the effect of antiresorptive and anabolic therapy on bone metabolism20-43 and in hormone replacement therapy.31,32,34,44,45 The determination of PINP concentrations has also been used to detect increases in type I collagen turnover in disease states such as renal osteodystrophy,46 primary hyperparathyroidism47 and Paget’s disease of bone.48-51 P1NP determination may be useful in assessing bone metastatic activity in malignancy and in predicting survival.52-54"