Magic 8am and Testosterone tests

[Dermotm55]

Why is it necessary to have a Testosterone test as close to 8am as possible? Is this because it is assumed that one goes to bed at midnight and sleeps for a solid 8 hours? Is it connected to daylight or circadian rhythm? Does it have to be done at 8am or as close as possible?

Because of my disturbed routine, I go to bed late and get up late. So I think that my '8am' is actually 11am.

Does it matter?

I tried going to bed at midnight last night, but couldn't sleep. Eventually I did sleep. I woke up at 8.20am. There was no morning erection and because I hadn't slept properly, I didn't get up for the test. At 11am I woke up again, but this time I had morning erection and so that is why I am thinkinng 11am might be a better time to have my blood test. Thoughts?

[PeakT]

For a normal sleep schedule, you get those LH pulses throughout the early morning which initiate the corresponding secretions of testosterone.  The reason you try to get your testosterone as close to 8 am as possible is that that is when testosterone peaks - actually a little before usually - and so you are getting the max read for the day.

Basically shift work modifies all of that in rather unpredictable ways.  For example, check out this study:

http://www.springerlink.com/content/w4633732864463r3/

And then look at this study where they examined a group of well-adjust men (to shift work) and found a pattern.  However, some guys deviated substantially from this pattern:

http://ajpregu.physiology.org/content/265/1/R261.short

So it sounds like assuming you are peaking at 8 am is not necessarily a given and perhaps you want to ask your doc if you can get a couple of reads similar to what they often do with cortisol?  Because you're not on HRT, right?  If you're on testosterone therapy, that's a different story of course.

On the other hand, peak to valley diminishes as we age and you're middle-aged, right?  If so, then it may not be worth the cost.  You'll have to discuss that with your doc, who hopefully knows something about the subject.  There's a little info here as well as far as the peak to trough ratio for different ages:

http://www.peaktestosterone.com/Testosterone_Daily