When to Check LH in Men
Check serum LH when testosterone is low to distinguish between primary testicular failure and secondary (hypothalamic-pituitary) hypogonadism, as this classification fundamentally determines whether fertility preservation is possible and guides treatment selection.
Primary Indications for LH Testing
Based on the most recent EAU guidelines 1, LH measurement is indicated in the following clinical scenarios:
1. Low Testosterone Levels (Essential)
- When morning total testosterone is confirmed low on repeat testing
- LH distinguishes primary hypogonadism (elevated LH with low testosterone) from secondary hypogonadism (low/normal LH with low testosterone)
- This distinction is critical: secondary hypogonadism patients can potentially achieve both fertility and normal testosterone with gonadotropin therapy, while primary hypogonadism patients require testosterone replacement which suppresses fertility 1
2. Male Infertility Evaluation
- Measure LH if sperm concentration is abnormally low 2
- Particularly important when considering fertility preservation options
- Helps identify treatable endocrine causes of infertility 2
3. Clinical Findings Suggesting Endocrinopathy
Check LH alongside testosterone when evaluating:
- Impaired sexual function 2
- Signs of hypogonadism (decreased libido, erectile dysfunction, reduced muscle mass, fatigue) 1
- Suspected pituitary disorders 1
4. Additional Testing When Low Testosterone Confirmed
If initial testosterone is low, the complete hormonal panel should include 2:
- Total and free/bioavailable testosterone
- LH
- Prolactin
Important Clinical Caveats
Timing Considerations
- Avoid testing during acute illness - this can artificially suppress the hypothalamic-pituitary-gonadal axis 1
- Morning samples are preferred for testosterone; LH can be measured simultaneously
- Consider that LH has pulsatile secretion patterns, though single measurements are generally adequate for clinical decision-making
Interpretation Pitfalls
- Elevated LH with normal testosterone in older men represents "compensated dysregulation" and is associated with deteriorating health, increased cardiovascular disease, and progression to primary hypogonadism 3
- This pattern is predicted by age >70 years, diabetes, chronic pain, and low physical activity 3
- Do not assume normal testosterone with elevated LH means no intervention needed - these men warrant closer monitoring
When LH Testing is NOT Needed
- Normal testosterone levels with no clinical symptoms of hypogonadism
- During testosterone therapy monitoring (LH will be suppressed by negative feedback) 4
- Isolated screening without clinical indication
Clinical Algorithm
- Suspect hypogonadism based on symptoms/signs or infertility
- Measure morning total testosterone (repeat if abnormal)
- If testosterone is low → Measure LH, prolactin, and free/bioavailable testosterone
- Interpret results:
- High LH + Low T = Primary hypogonadism → Testosterone therapy only
- Low/Normal LH + Low T = Secondary hypogonadism → Gonadotropin therapy if fertility desired, or testosterone therapy
- Consider fertility goals before initiating any treatment, as testosterone therapy is contraindicated in men seeking fertility 1
The key principle: LH measurement is not a screening test but a diagnostic tool to classify the type of hypogonadism once testosterone deficiency is confirmed, enabling appropriate treatment selection that considers both symptom relief and fertility preservation.