Androgenic Allopecia is caused by excessive Dihydrotestosterone (DHT), or at least that is one of the mechanisms currently recognized. It is usually caused either by an excess of Testosterone, or a dysfunction of it's metabolism turning it more quickly into DHT.
Ketoconazole is not "good" for hair, in that it does not improve it's quality or have much effect on the growth process of the hair. Ketoconazole is good for Androgenic Allopecia, due to it's Androgenic Antagonism. As an androgenic antagonist, it inhibits the action of DHT. While taken systemically it can inhibit the synthesis of Androgens, taken topically it just stops the effects of excess DHT at the hair follicle, itself.
However, there are really no long-long term studies (measured in years) on how it might affect androgen synthesis when taken topically. An acute topical does does nothing in that respect, but having that on your scalp every day, maybe a bit seeping into your skin, a bit getting in your eyes, nose, mouth, or other mucous membranes, over a period of years, might actually have a systemic effect. For those who are using Ketoconazole for true androgenic allopecia, this would not be noticed and might help it's effects, but for this situation you are describing.
Reguardless of the source of your low T levels, they are not causing androgenic allopecia. If your DHT is low, too, then something else is at play, and Ketoconazole is not going to be your magic bullet.
Did you mention the Nizoral to the doctor? If so he may have assumed that you found it useful for hair loss, he drew some conclusions from that, and assumed you were self-medicating Androgenic Allopecia... hence the Rogaine suggestion.
Edited by Jeoshua, 21 February 2014 - 05:08 PM.