Elderly men with low
testosterone (T) levels are increasingly diagnosed to have partial
androgen deficiency of the aging male (PADAM). Frequently, magnetic resonance imaging is performed to exclude
pituitary adenoma. The value of
GnRH testing to differentiate PADAM from secondary
hypogonadism is unknown. Serum levels of T as well as LH and FSH at baseline and after
GnRH were evaluated in the following groups: 1) 24 elderly men with low serum T (<11.7 nmol/liter), 2) 25 elderly men with normal serum T levels (>11.7 nmol/liter), 3) 10 men with primary
hypogonadism, 4) 24 men with secondary
hypogonadism, and 5) 13 healthy young volunteers. In elderly men, T levels were lower (P < 0.001) and
gonadotropin levels higher (P = 0.03) compared with younger controls. LH and FSH response to
GnRH was higher in elderly men with low T levels (PADAM) compared with elderly men with normal T levels (P = 0.02 and P < 0.001) in the presence of similar basal
gonadotropin levels. To differentiate secondary
hypogonadism from PADAM with a sensitivity of 100%, a T less than 10 nmol/liter had a specificity of 50%. This specificity was improved to 75% by using a cutoff of less than or equal to 15 mU/liter increase of LH upon
GnRH stimulation. Overall, decreased T levels and increased LH levels in elderly men suggest a primary Leydig cell dysfunction. In the subgroup of elderly men with low T levels, an increased LH response to
GnRH with normal basal LH levels suggests additional, possibly hypothalamic changes. To exclude secondary
hypogonadism in PADAM, diagnostic accuracy can be improved by using
GnRH testing.