Why check Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) levels?

Why Check LH and FSH Levels

LH and FSH measurements are essential diagnostic tools for distinguishing between primary and secondary hypogonadism, evaluating reproductive disorders, and monitoring treatment effectiveness in patients with hormonal imbalances. 1

Primary Diagnostic Applications

Hypogonadism Classification

• Primary hypogonadism: Characterized by testicular/ovarian failure with elevated LH and FSH levels due to lack of negative feedback
  • Causes include: cryptorchidism, bilateral torsion, orchitis, vanishing testis syndrome, orchiectomy, Klinefelter's syndrome, chemotherapy, or toxic damage 2
• Secondary hypogonadism: Characterized by hypothalamic-pituitary dysfunction with low or inappropriately normal LH and FSH levels
  • Causes include: gonadotropin or LHRH deficiency, pituitary-hypothalamic injury from tumors, trauma, or radiation 2

Specific Clinical Scenarios

In Males:

• Cryptorchidism evaluation: In boys with bilateral nonpalpable testes, LH and FSH measurements help evaluate for anorchia 3
• Delayed puberty assessment: FSH combined with inhibin B or AMH is highly predictive in distinguishing between self-limited delayed puberty and congenital hypogonadotropic hypogonadism 4
• Testosterone deficiency workup:
  • Morning LH levels help determine if hypogonadism is primary or secondary 1
  • Measure serum prolactin if LH levels are low or low/normal 1
  • Consider pituitary MRI if total testosterone <150 ng/dL with low/normal LH 1

In Females:

• Amenorrhea evaluation:
  • Baseline LH, FSH, and estradiol levels should be assessed at age 13 years in at-risk patients 3
  • Helps differentiate between primary ovarian failure (high FSH/LH) and hypothalamic dysfunction (low/normal FSH/LH) 3
• Premature ovarian failure (POF) assessment:
  • Elevated FSH/LH levels indicate ovarian failure 3
  • Risk factors include alkylating chemotherapy, ovarian radiation, and certain genetic conditions 3
• Functional hypothalamic amenorrhea (FHA):
  • Low LH levels, especially with a LH:FSH ratio <1, suggest FHA 3
  • Often associated with energy deficit, excessive exercise, or psychological stress 3

Monitoring Applications

Treatment Response Monitoring

• Testosterone replacement therapy:
  • LH and FSH levels decrease with testosterone treatment, confirming adequate suppression of the hypothalamic-pituitary axis 2
• Gonadotropin therapy:
  • For secondary hypogonadism patients seeking fertility, monitoring response to recombinant hCG and FSH therapy 3

Disease Progression Monitoring

• Cancer survivors: Regular screening of LH/FSH in patients at risk of hypogonadism to identify gonadotropin deficiency, delayed puberty, or premature ovarian failure 3
• Chronic liver disease: LH/FSH measurements help diagnose hypogonadism, which is common in advanced liver disease 3

Clinical Pearls and Pitfalls

Important Considerations

• Timing matters:

  • Testosterone and associated hormone tests should be drawn in the morning due to diurnal variation 1
  • Multiple samples over time may be required to diagnose gonadotropin deficiency in adolescents 5

• Interpretation challenges:

  • Single measurements may be insufficient due to pulsatile secretion patterns 6
  • SHBG levels affect interpretation of total testosterone results - high SHBG is the most common cause of normal total testosterone with low free testosterone 1

Common Pitfalls

• Acute illness: Avoid testosterone testing during acute illness as it can temporarily suppress levels 3
• Obesity effects: Increases aromatization of testosterone to estradiol, which can suppress LH secretion 1
• Medication interference: Check for drugs that may interfere with the hypothalamic-pituitary axis 3

Treatment Implications

• Primary vs. Secondary Hypogonadism:

  • Primary: Testosterone therapy only (compromises fertility) 3
  • Secondary: Potential for both fertility and normal testosterone with appropriate treatment (gonadotropin therapy) 3

• Fertility considerations:

  • Testosterone therapy is contraindicated in men seeking fertility 1
  • For secondary hypogonadism, gonadotropin therapy is standard for fertility preservation 3

By properly interpreting LH and FSH levels in clinical context, providers can accurately diagnose reproductive disorders, guide appropriate treatment selection, and monitor therapeutic effectiveness.