Luteinizing Hormone (LH) Measurement: Clinical Significance and Interpretation
Luteinizing hormone (LH) is a gonadotropin hormone that helps establish the etiology of testosterone deficiency in men and plays a crucial role in reproductive function in both sexes. 1
What LH Measures
Luteinizing hormone is a gonadotropin secreted by the anterior pituitary gland that serves several key functions:
- In men: Stimulates Leydig cells in the testes to produce testosterone
- In women: Triggers ovulation and stimulates the ovaries to produce estrogen and progesterone
LH measurement provides critical information about:
- The functional status of the hypothalamic-pituitary-gonadal (HPG) axis
- The source of hormonal abnormalities (primary vs. secondary)
- Reproductive health and fertility potential
Clinical Applications of LH Testing
In Male Patients
Testosterone deficiency evaluation: LH helps differentiate between:
- Primary hypogonadism (testicular failure): Elevated LH with low testosterone
- Secondary hypogonadism (pituitary/hypothalamic dysfunction): Low or inappropriately normal LH with low testosterone 1
Fertility assessment: LH measurement is essential in men with infertility concerns 1
Pituitary function: Low LH with low testosterone may indicate pituitary disorders requiring further evaluation, including MRI 1
In Female Patients
- Ovulation detection: Mid-cycle LH surge indicates impending ovulation
- PCOS diagnosis: LH:FSH ratio >2 may suggest polycystic ovary syndrome 2
- Menopause confirmation: Elevated LH levels occur in postmenopausal women
Interpretation Guidelines
Men
- Normal range: 0.6-3.2 mIU/mL (may vary by laboratory) 3
- Elevated LH + low testosterone: Indicates primary testicular failure
- Low/normal LH + low testosterone: Indicates secondary hypogonadism (pituitary/hypothalamic origin)
- Requires additional testing, including prolactin measurement 1
- May indicate pituitary tumors or other central disorders
Women
- Normal range: Varies throughout menstrual cycle
- Post-menopausal: Elevated levels (4.5-10.5 mIU/mL) 3
Clinical Recommendations for LH Testing
Always measure LH in patients with low testosterone to establish the etiology of testosterone deficiency (Strong Recommendation; Grade A) 1
Measure serum prolactin in patients with low testosterone combined with low/normal LH levels to screen for hyperprolactinemia (Strong Recommendation; Grade A) 1
Consider pituitary MRI for men with total testosterone <150 ng/dL and low/normal LH regardless of prolactin levels, as non-secreting adenomas may be present 1
Perform reproductive health evaluation in men with testosterone deficiency who are interested in fertility, including testicular examination and FSH measurement 1
Common Pitfalls in LH Interpretation
- False elevations: Can occur with marijuana use and hypogonadism 1
- Diurnal variation: Morning samples are preferred for accurate assessment
- Screening limitations: LH is not recommended as a screening test for germ cell tumors in asymptomatic adults 1
- Isolated measurement: LH should be interpreted in conjunction with other hormones (testosterone, FSH, prolactin) for comprehensive evaluation
Key Points to Remember
- LH measurement is essential in diagnosing the cause of hypogonadism in men
- LH levels help guide treatment decisions, particularly regarding fertility preservation
- The pattern of LH secretion (normal, elevated, or suppressed) provides crucial information about the site of hormonal dysfunction
- Abnormal LH levels may indicate the need for additional testing, including pituitary imaging
- LH measurement is part of a comprehensive hormonal assessment and should not be interpreted in isolation
LH testing is a valuable diagnostic tool that provides critical information about reproductive function and hormonal status, guiding appropriate treatment decisions and identifying patients who require further specialized evaluation.