Clinical Explainer
Biomarker 101: Understanding Your TRT Labs
One TRT lab panel covers more than testosterone. What total and free T, SHBG, LH, FSH, and the rest of the panel are actually monitoring.
When you come to us for testosterone therapy (TRT), we draw one comprehensive lab panel — your TRT blood work — because testosterone does not work alone. Treating it properly means looking at the systems around it too: other hormones, your metabolism, the prostate, your blood count, pituitary gland and thyroid. Here is what we are monitoring and why.
Checking testosterone levels: Total, Free, SHBG, LH & FSH
- Total testosterone
- Free testosterone
- SHBG (Sex Hormone-Binding Globulin)
- LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone)
Most of the testosterone circulating in the blood is attached to a protein and cannot do much in that state. Only the unbound portion, called free testosterone, is available for tissues to use. That protein is SHBG, sex hormone-binding globulin, made mostly by the liver, and it is the reason total testosterone is never looked at by itself. Two men can post the same total testosterone number and have noticeably different amounts of it available to their bodies, because one of them has far more SHBG soaking up the supply. The total describes how much testosterone exists. The ratio between total and SHBG describes how much of it the body can use.
Testosterone production does not begin in the testes, but rather, in the brain, where the hypothalamus and pituitary gland send out LH and FSH, hormones that signal and instruct the testes to produce testosterone. We check both these values because high LH and FSH alongside low testosterone tells us that the signal from the brain is strong, but the testes are not responding. A low or unremarkable LH and FSH alongside low testosterone tells us the signal itself is weak, and that we need to look further into the pituitary or hypothalamus.
Related Hormones: Estradiol, Prolactin & DHEA-S
- Estradiol
- Prolactin
- DHEA-S
Some testosterone in the body is converted by an enzyme called aromatase into estradiol, the most potent form of estrogen, which is involved in bone density, joint tissue, and libido, in men just as in women. Because estradiol is made directly from testosterone, its levels will change in relation to testosterone levels, which is why we read the two together rather than separately.
Prolactin is not part of the testosterone production pathway, but because it is also made by the pituitary gland, it gives us a window into how that gland is working overall, sitting alongside LH and FSH as another data point on pituitary function.
