CTX and P1NP are the most popular bone turnover markers nowadays due to their sensitivity to change, or magnitude in change during a drug therapy and smaller variation (error bar for a data point) when compared to other bone markers such as NTx or bone ALP.

Among the two bone markers, CTX has a very wide reference range, reflecting large variation among different individuals as well within an individual. The influencing factors that are uncontrollable include age, gender, menopausal status, ethnicity, disease and drug, and fracture, etc. The following is a list of factors which can be controlled:
•circadian rhythms
•food intake
•menstrual
•seasonal
•exercise
•life style
Circadian rhythms and food intake plays a big part in daily ebb and flow of CTX. For example, CTX peaks at 01:30-04:30am, and bottoms at 11:00am-03:00pm. Food in the morning could decrease CTX reading as much as ~18%.

To summarize, in order to get a more accurate reading of CTX, it’s best to:
•fast in the morning;
•do an early morning 8-9am testing (within one hour of waking up if feasible) and be consistent in timing of blood drawing (set an appointment online!);
•stop collagen and biotin supplements 48-72hours before blood drawing;
•refrain from physical activity with high intensity for 24-48 hours. Daily walking should be fine
•stick with a same lab as different assays may be used at different labs

P1NP has very small fluctuations so get it done at the same time of CTX testing should give you a pretty reliable reading.

Bear in mind that there are so called “non-responders” whose bone marker testings do not show much changes (change greater than LSC -least significant change) during an antiresorptive or anabolic therapy. For instance, on average there are about 98% of responders to Alendronate/Fosamax at 12 weeks of treatment, 2% (2 out of 100 ppl on average) won’t have bone marker changes. This non-responder phenomenon applies to most of osteodrugs.

Hope other members also chime in with this topic to make the list complete so everyone could be better prepared for the tests and get most out of the labs.

Anyone has any take on VitD? Personally I kept taking my dose daily without modification in regard to bone marker testing.