From the Guidelines
To evaluate erectile dysfunction, I recommend ordering both total testosterone and free testosterone levels, as well as luteinizing hormone (LH) and follicle-stimulating hormone (FSH) to determine the underlying cause of hypogonadism, if present. These tests should be drawn in the morning (between 8-10 AM) when levels are highest, and preferably after fasting. If the initial total testosterone level is low (typically below 300 ng/dL), the test should be repeated to confirm the finding, as recommended by the American Urological Association (AUA) guideline 1. Additional helpful labs include sex hormone-binding globulin (SHBG) to assess free testosterone availability and prolactin to rule out hyperprolactinemia, which can suppress testosterone production. These comprehensive measurements are important because testosterone deficiency contributes to erectile dysfunction in a significant proportion of cases, but other factors like vascular disease, neurological conditions, and psychological issues often play significant roles as well 1. It is essential to note that the diagnosis of testosterone deficiency requires both a low testosterone measurement and the presence of select symptoms and/or signs, as stated in the AUA guideline 1. Therefore, a thorough clinical evaluation, including a targeted physical exam and patient-reported symptoms, is necessary to determine the need for testosterone therapy.
From the Research
Testosterone Labs for Erectile Dysfunction
To evaluate erectile dysfunction, several testosterone labs can be ordered, including:
- Morning serum total testosterone level 2
- Free or bioavailable testosterone measurement, especially in conditions that alter sex-hormone-binding globulin (SHBG) levels, such as in the elderly and in obesity 3
- Sex hormone-binding globulin (SHBG) measurement to calculate free testosterone (FT) 4
- Luteinizing hormone (LH) measurement to screen for hypogonadism 4
Rationale for Testosterone Labs
The rationale for ordering these labs is to:
- Screen for hypogonadism, which is a common comorbidity in patients with erectile dysfunction 5
- Evaluate the role of testosterone in erectile function, as testosterone may facilitate erection by acting as a vasodilator of the penile arterioles and cavernous sinusoids 3
- Identify patients who may benefit from testosterone replacement therapy, particularly those with severe hypogonadism 3, 2
- Monitor the effectiveness of testosterone replacement therapy in improving erectile function and libido 2, 5
Limitations of Testosterone Labs
It is essential to note that:
- Total testosterone measurement alone may not be sufficient to exclude hypogonadism in patients with erectile dysfunction, especially in older men with elevated SHBG levels 4
- The prevalence of normal total testosterone with low free testosterone is frequent in patients with erectile dysfunction, and current screening recommendations may miss biochemical hypogonadism in these patients 4