MKSAP Quiz: Evaluation for decreased libido, erectile dysfunction
A 58-year-old man is evaluated for decreased libido and erectile dysfunction that began insidiously over the past 6 months. He is not having nocturnal or early morning erections. His medical history is otherwise unremarkable. Following a physical exam and lab studies, what is the most appropriate management?
A 58-year-old man is evaluated for decreased libido and erectile dysfunction that began insidiously over the past 6 months. He is not having nocturnal or early morning erections. His medical history is otherwise unremarkable.
On physical examination, vital signs are normal. BMI is 24. There is no gynecomastia. Distribution of pubic hair is normal. Testes are normal sized.
Laboratory studies show an 8:00 AM serum total testosterone level of 200 ng/dL (6.94 nmol/L) and a thyroid-stimulating hormone level of 3.6 µU/mL (3.6 mU/L).
Which of the following is the most appropriate management?
A. Measure serum free testosterone level
B. Measure serum luteinizing hormone level
C. Repeat 8:00 AM serum total testosterone measurement
D. Start intramuscular testosterone therapy
E. Start sildenafil
MKSAP Answer and Critique
The correct answer is C. Repeat 8:00 AM serum total testosterone measurement. This content is available to MKSAP 19 subscribers as Question 113 in the General Internal Medicine 2 section. More information about MKSAP is available online.
The most appropriate management is repeat measurement of the 8:00 AM serum total testosterone level (Option C). The diagnosis of androgen deficiency should be made only when a patient has two separate early morning (8:00 AM) serum total testosterone levels less than 300 ng/dL (10.41 nmol/dL) combined with suggestive symptoms and/or signs. This patient has an 8:00 AM serum total testosterone level of 200 ng/dL (6.94 nmol/L) and symptoms of sexual dysfunction (decreased libido and erectile dysfunction), suggesting androgen deficiency. The most appropriate management at this time is to repeat the 8:00 AM serum total testosterone measurement to confirm this diagnosis.
Obtaining a serum free testosterone level (Option A) can be helpful when alterations in sex hormone–binding globulin (SHBG) levels may be causing serum total testosterone levels to be unreliable. Alterations in SHBG levels occur in older men with obesity; men with advanced liver disease, diabetes, or insulin resistance; and men who use glucocorticoids. There is no concern that this patient has an alteration in his SHBG level, and obtaining a serum free testosterone level is not indicated.
An elevated luteinizing hormone (LH) level (Option B) with simultaneous low testosterone indicates primary (testicular) hypogonadism. A low or normal LH level with simultaneous low testosterone indicates secondary hypogonadism. Confirming the presence of hypogonadism is necessary before assessment with LH measurement.
Starting intramuscular testosterone therapy (Option D) before obtaining a second, confirmatory 8:00 AM serum total testosterone level is not recommended. If the second serum total testosterone level is low, intramuscular testosterone therapy can be considered. Intramuscular testosterone is less costly than transdermal formulations and has similar efficacy and safety.
Oral phosphodiesterase-5 (PDE-5) inhibitors, such as sildenafil (Option E), are first-line medical therapy for erectile dysfunction and are safe and effective in most patients. Testosterone therapy may also be indicated in cases of confirmed androgen deficiency. When prescribed for hypogonadal men with erectile dysfunction, testosterone therapy will enhance the efficacy of PDE-5 inhibitors. However, neither PDE-5 inhibitors nor testosterone therapy is indicated until the patient is fully evaluated for hypogonadism.
Key Points
- The diagnosis of androgen deficiency should be made only when a patient has two separate early morning (8:00 AM) serum total testosterone levels less than 300 ng/dL (10.41 nmol/dL) combined with suggestive symptoms and/or signs.
- Free and bioavailable testosterone measurements should be reserved for patients with total testosterone levels in the low-normal range and for patients suspected of having alterations in sex hormone–binding globulin levels.