Low LH in a 50-Year-Old Man: Secondary Hypogonadism
Low LH in a 50-year-old man with low testosterone indicates secondary (hypogonadotropic) hypogonadism, meaning the problem originates in the hypothalamus or pituitary gland rather than the testicles. 1
Understanding the Diagnosis
What Low LH Means:
- When testosterone is low and LH is also low or inappropriately normal (not elevated), this indicates the pituitary is not responding appropriately to low testosterone levels 1
- In primary testicular failure, you would expect LH to be elevated as the pituitary tries to stimulate failing testicles 1
- Low or low-normal LH with low testosterone points to a problem at the hypothalamic-pituitary level 1
Common Causes to Investigate
Functional/Reversible Causes (Most Common in 50-Year-Olds):
- Obesity and metabolic syndrome—increased aromatization of testosterone to estradiol in adipose tissue causes estradiol-mediated negative feedback suppressing LH secretion 1
- Type 2 diabetes mellitus 1
- Chronic systemic diseases (HIV, chronic organ failure, chronic inflammatory conditions) 1
- Medications: opiates, glucocorticoids, anabolic steroids, GnRH agonists/antagonists 1
- Sleep disorders and obstructive sleep apnea 1
Structural/Organic Causes (Less Common but Critical to Rule Out):
- Pituitary tumors (prolactinomas, non-secreting adenomas) 1
- Hyperprolactinemia from any cause 1
- Traumatic brain injury 1
- Prior pituitary surgery or cranial irradiation 1
- Infiltrative diseases (sarcoidosis, hemochromatosis) 1
Required Workup
Immediate Laboratory Tests:
- Repeat morning testosterone (8-10 AM) on at least two separate occasions to confirm persistent hypogonadism 1, 2
- Serum prolactin level—if elevated, repeat to confirm and consider pituitary MRI 1
- Free testosterone by equilibrium dialysis, especially if total testosterone is borderline 1, 2
- Sex hormone-binding globulin (SHBG) to distinguish true hypogonadism from low SHBG-related decreases 1, 2
Additional Evaluation if Testosterone <150 ng/dL:
- Pituitary MRI regardless of prolactin levels, as non-secreting adenomas may be present 1
Screening for Reversible Causes:
- Fasting glucose and HbA1c (diabetes screening) 1
- Iron saturation (hemochromatosis) 1
- TSH (thyroid dysfunction) 1
- Medication review for testosterone-suppressing drugs 1
Treatment Implications
Critical Distinction from Primary Hypogonadism:
- Men with secondary hypogonadism who desire fertility must receive gonadotropin therapy (hCG plus FSH), not testosterone replacement 1, 2
- Testosterone therapy is absolutely contraindicated in men seeking fertility preservation, as it causes azoospermia 1, 2
- Secondary hypogonadism patients can potentially achieve both fertility restoration and normal testosterone with gonadotropin therapy 2
If Fertility is Not a Concern:
- Address underlying reversible causes first (weight loss, optimize diabetes control, discontinue offending medications) 1, 2
- Weight loss through low-calorie diets can improve testosterone levels in obesity-associated secondary hypogonadism 1, 2
- If testosterone remains low after addressing reversible causes, testosterone replacement therapy can be considered 1, 2
Expected Treatment Outcomes with Testosterone Therapy:
- Small but significant improvements in sexual function and libido (standardized mean difference 0.35) 2
- Little to no effect on physical functioning, energy, vitality, or cognition 2
- Modest improvements in metabolic parameters (insulin resistance, glycemic control, lipid profile) 1, 2
Critical Pitfalls to Avoid
- Never start testosterone without confirming the patient does not desire fertility 2
- Never diagnose hypogonadism based on symptoms alone—biochemical confirmation with low testosterone on two separate morning measurements is mandatory 1, 2
- Never skip investigation for secondary causes—reversible conditions (obesity, medications, pituitary tumors) must be addressed first 1, 2
- Never assume age-related decline in a 50-year-old man—this age group warrants full investigation for organic causes 2, 3