T Nation

Reference Ranges


Hello all
I’d like to understand why reference ranges vary so widely. For example … My Free test serum. number is 26.6 on a scale of 4.26 - 16.4 (sorry no unit measure listed probably ng/dl) and my bio avail. test is 431 ng/dl on a scale of 61-213ng/dl. Total test is 783 ng/dl on a range of 240-950. These ranges are from Mayo clinic. My Doc is concerned about these “high” free test numbers. However, looking at Quest diagnostics bio avail. test range is 110 - 575 ng/dl and free test is 46-224 pg/ml = 4.6-22.4 ng/dl. I am wondering why my numbers are so high given my reasonable total test number but regardless why such a difference in ranges??


FT ranges simply vary from one lab to another, reflecting the fact that something really is wrong.

You can expect some variations as labs establish ranges with different sample groups.

As for your FT: The goal of TRT is high normal or higher youthful T levels. You may be getting range info that is age adjusted for older sample groups. You do not want to have high range for old men.