When taking CTX the timing of the blood draw must be as early as possible - as soon as the lab opens. CTX has a natural spike and decline throughtout the day. It is highest somewhere in the 3-5 am timeframe and then declines throughout the day and then builds again.. Ive heard different estimations. Therefore take it at 6am if thats when youe lab opens and the next time you take it, arrange it to be the same time. CTX can drop substantially throughout the day and you will not get an accurate comparison.
I have a current range of 535 at about 6am. Within 2 weeks of a CTX, I had a set of labs done by another doc that could not be done until 9;15am due to a restriction. I did not know a CTX was included in those new labs. MY result was 430 - but that was 3 hours after my 'baseline; CTX ( 6am ) so it was not menaingful. This may be one reason some doc do not use BTM - becasue they are specific. I think however, if the patient is given clear instructions,we will follow them.
On another point, I have had 5 - 24 hour urine c calcium tests done. ONly my last doc told me to stop supplemental calcium 24r prior, as additional calcium will sque results.. It makes sense there will be spillage of excess calcium if taking supplements - but I wasnt given the insturction. I know so much more than when I began, I hope anything I learned may help others.