In our institution, testosterone and androstenedione are measured simultaneously using LC-MS/MS and I have come across patients with clinical signs of androgen excess who have normal testosterone levels/FAI but have high androstenedione levels. I found that the correlation coefficient between the regular FAI and an androstenedione FAI in a healthy female subject group (n=75) to be r = 0.9004. I have come across one paper that touches on this subject, I'm just wondering is there any other information people might have regarding this topic
Dear Shane,
I am just wondering how you calculated the FAI based on androstenedione (A), but I presume you calculated A/SHBG. However, A is not bound to SHBG, it is only loosely bound to albumin and other proteins in the circulation. As for testosterone (T), steroids bound to these proteins are usually considered as "free". It is not surprising that you find a good correlation between FAI based on T and FAI based on A, since levels of A and T in women are correlated with each other, If you divide both by the same SHBG concentration, you will get the same correlation you also find between the total T and A levels.
I hope this answers your question.
Frank de Jong
Hi Frank,
Firstly, thank you for your help, its much appreciated. Yeah the FAI based on (A) was just calculated by just A/SHBG. I understand now. I thought as much that SHBG didn't bind A but in the paper I have attched, it states.. "By virtue of its much decreased binding to SHBG, however, androstenedione has higher bioavailability in serum than does testosterone and thus has important androgenic potential"... and this statement led me to believe that SHBG-A binding actually does occur.
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