Here's an example, where a person has good testosterone levels but still no libido, while on Depo-Testosterone as the only treatment:
To help in understanding the labs, I did some conversions to U.S. units.
Total Cholesterol: 3.19nmol/L (3.57-5.20) = LOW
Trig: 0.8nmol/L (0.0-2.3) = LOW NORMAL
TSH: 1.33uIU/ml (0.27-4.2) = LOW NORMAL
T3: 1.7 nmol/l(1.3-3.1) = LOW NORMAL
T4: 69nmol/l (63-151) = LOW NORMAL
E2: 62pmol/L (26-165) = 16.9 pg/ml = LOW NORMAL
Progesterone: 2.21nmol/l (<0.95) = 0.69 ng/ml = LOW NORMAL
Cortisol: 331nmol/l (221-690) = 12.0 mcg/dl = LOW NORMAL
Total
Test: 21.8 (5.2-22) = HIGH NORMAL
Free
Test: 175pmol/l (45-149) = HIGH
SHBG: 7.23nmol/l (13-71) = LOW
DHT: 2.58nmol/l (1.13-4.13) = NORMAL
The current lab panel is missing a lot of information, but some thoughts that come to mind include:
SEX HORMONE BINDING GLOBULIN (SHBG) has many functions. A very important function is to bind to its own receptors on cells to transmit signals to the cell depending on whether or not estrogen or testosterone is bound to it. A speculated result of such signals is to increase the production of estrogen or testosterone receptors on the cell - making the cell more sensitive to estrogen or testosterone. Whether or not it is important for libido is speculative, but I would not doubt that it plays a role. A second function is to prolong the life of circulating testosterone,
DHT, and estrogens. Testosterone, otherwise, would last only 10-100 minutes. Testosterone bound to SHBG is our body's natural depo-testosterone.
SHBG is produced by the liver in response to estrogen and thyroid hormone. SHBG production is inhibited by testosterone, DHEA,
DHT, other androgens, insulin, and growth hormone. When thyroid is low or estrogen is low, SHBG may be low. When free testosterone (and other androgens), DHEA, insulin (such as during insulin resistance or diabetes type 2) or growth hormone is too high, then SHBG may be low. One way of looking at it is that it is a balancing act in the body to prevent excessive levels of anabolic hormones.
THYROID HORMONE when at optimal levels for the person play a role in maintaining libido. Thyroid hormone has mood elevating effects, allows energy production needed for sex, increase sperm production, and increases steroid hormone production (e.g. testosterone) in the testes. There are thyroid hormone receptors in the cells of the testes.
THYROID RELEASING HORMONE: Interestingly, in addition to the hypothalamus of the brain, the testes also release Thyroid Releasing Hormone (TRH). No one has yet explored this idea in the literature, but TRH can go to the pituitary gland and cause it to release Thyroid Stimulating Hormone (TSH), which then causes the thyroid gland to release thyroid hormone.
ADRENAL FATIGUE can stop libido. Lab
test findings may include low to low normal progesterone, low to low normal DHEA, low normal cortisol, low testosterone (in perimenopausal women), among other findings discussed in the adrenal thread. Mood swings, irritability, anxiety, lack of energy, feeling burnt out, lack of enthusiasm, lack of libido, etc., are some symptoms. Adrenal fatigue can hide the presence of insulin resistance since low cortisol levels lead to low production of blood glucose, which then lowers blood levels of insulin.
DHEA from the adrenal glands plays a prominent role in reducing SHBG so that more testosterone can be freed to work. When adrenal fatigue is present, SHBG can be high despite normal estrogen, thyroid hormone levels, and testosterone levels because DHEA is low. This can result in low free testosterone and impaired libido.
PROGESTERONE plays a role in libido. It has anxiolytic, mood stabilizing, and antidepressant effects. It allows thyroid hormone to function. It increases neurotransmitter levels in the brain including dopamine. It is the precursor for both cortisol and testosterone. It is generally reduced in level when adrenal fatigue is present. Excessive progesterone, however, can inhibit libido. Excessive progesterone can also overly increase the production of estrogen receptors - resulting in gynecomastia, among other things (such as bleeding in menopausal women). Generally, I prefer at least mid-range values for progesterone in patients.
ESTRADIOL (E2) is the most potent natural estrogen. The value obtained by measuring Estradiol alone (i.e. not obtaining fractionated estrogens) is actually a measure of total estrogens since it varies depending not only on the presence of estradiol but the other estrogens. As such, getting an E2 alone gives some measure of total estrogens.
Estrogen helps determine sexual aggression. To me, this means libido. Thus when estrogen (e.g. estradiol) is too low, there is no libido.
When estrogen is too high, there is also reduced or no libido. One rationale is that estrogen competes with thyroid hormone for thyroid hormone receptors. Progesterone helps prevent this. But if estrogen is too high, estrogen will end up blocking thyroid hormone function - including thyroid hormone's role in promoting libido. Another rationale is that estrogen is a monoamine oxidase inhibitor. It increases primarily serotonin and norepinephrine. At too high a level, these can inhibit libido.
Some clinicians expressed preference for an estradiol of around 32 pg/ml for optimal libido in men. However, this will depend on all the factors that determine libido. Some need more. Some need less.
When estradiol is low, the use of an aromatase enzyme such as Arimidex is not the first thing that I would do to solve the problem of lack of libido.
HOT FLASHES are a symptom of ESTROGEN WITHDRAWAL. When estrogen level is reduced, one gets hot flashes.
AROMATASE ENZYME: Estradiol is produced by the aromatase enzyme from Testosterone.
LUTEINIZING HORMONE (LH): What controls the production of aromatase? Among other things, LUTEINIZING HORMONE increases the production of aromatase enzyme. When Free testosterone and
DHT are high enough, the release of Luteinizing Hormone from the brain is reduced. This may lead to reduced production of aromatase and thus estrogen production. LH also helps increase the production of the side cleavage enzyme that starts the first step in converting cholesterol to the steroid hormones.
LOW CHOLESTEROL: indicates that a person may have difficulty in producing steroid hormones.
HUMAN CHORIONIC GONADOTROPIN (HCG) is an analog to LH, FSH, and THYROID HORMONE.
TRT: A Recipe for Success 
Roy