answered Dec 23, 2009 at 06:56PM
In general, decreases in sex drive can be divided into two groups: biological and psychological. The biological group includes things like decreased testosterone (from things such as testicular atrophy or pituitary gland problems). A normal testosterone level makes biologic cause for decreased libido unlikely.
The other cause, psychological, can be attributed to things such as depression or anxiety. There is no specific test for these conditions and these are best evaluated by a physician.
The important question to ask is whether one has decreased libido or decreased interest in human women. With decreased libido, one is not interested in sex or masturbation. If one still has interest in either, it is less likely decreased libido and could be paraphilia or other psychological cause. A psychiatrist can assist in making this determination and helping to restore normal sex function.