There are people on this board that know much more than me about this; however, this is my two cents.
First you need to see which testosterone value you are looking at. There is Free, Bound and Total testosterone. Total for a person under 20 is between 241 and 827. However, the value that is probably more important is the Free. Free testosterone is the testosterone that is not bound up and can potentially find a receptor. A person can have a high Total Testosterone and a low Free Testosterone level. For a person over 18 the normal values for Free Testosterone range between 34 and 194.
Now, getting to how you could have a high Total and low Free Testosterone. The two major troublemakers are Estrogen and SHBG. They work against your Free Testosterone levels. When getting a blood test for testosterone, always check your Estrodial and SHBG as well. Estrodial is you estrogen level. Estrogen levels will increase as you increase your testosterone levels. This is a problem since estrogen fights with Free Testosterone for receptors. Unfortunately the estrogen can win the fight for the receptor. It can even knock testosterone off of a receptor in its fight. Also, the higher your estrodial the higher your SHBG will go. SHBG is Sex Hormone Binding Globulin. This stuff is your bodies’ way to lower your testosterone if it thinks it is too high. Your body checks its estrogen level to determine how much SHBG to release. SHBG sticks to testosterone in the blood rendering it unable to attach to a receptor and thus creating Bound Testosterone.