What laboratory tests are recommended for evaluating low libido?

Laboratory Tests for Evaluating Low Libido

For patients presenting with low libido, comprehensive laboratory testing should include total and free testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, thyroid function tests, and morning cortisol levels to identify underlying hormonal causes.

Primary Hormone Panel

• Testosterone Assessment:

  • Total testosterone 1, 2
  • Free testosterone or androgen index (preferred over total testosterone alone) 1, 2
  • Timing: Morning collection (when levels are highest)

• Other Essential Hormones:

  • Luteinizing hormone (LH) 3, 1
  • Follicle-stimulating hormone (FSH) 3, 1
  • Prolactin (particularly in patients with hypogonadism) 2
  • Thyroid function: TSH and free T4 3
  • Morning cortisol and ACTH 3

Rationale and Evidence

Free testosterone measurement is particularly valuable as it:

• Can prevent unnecessary endocrine investigation in up to 50% of men with low total testosterone 1
• Provides more accurate assessment of bioavailable testosterone 2
• Better correlates with symptoms of low libido 4

Prolactin should be measured in patients with:

• Confirmed hypogonadism (low testosterone) 2
• History of decreased libido 2

Additional Testing Based on Clinical Presentation

• For patients with multiple endocrine abnormalities or severe headaches:

  • Consider MRI brain with pituitary/sellar cuts 3

• For patients with cardiovascular risk factors:

  • Complete metabolic panel 1
  • Lipid profile 3
  • Hemoglobin/hematocrit (baseline and monitoring) 1

• For patients with suspected adrenal insufficiency:

  • Standard-dose ACTH stimulation testing (for indeterminate results) 3
  • DHEA levels (particularly in women with low libido) 3

Clinical Pearls and Pitfalls

• Hypogonadism is found in approximately 15.6% of men presenting with sexual dysfunction 2
• Clinical symptoms and physical examination alone (including history of decreased libido or testicular atrophy) cannot reliably predict hypogonadism, making laboratory testing essential 2
• The relationship between testosterone and libido is statistically significant but modest; other factors often contribute to low libido 4
• Target total testosterone levels should be 450-600 ng/dL (mid-normal range) when considering treatment 1
• Low libido can have multiple causes beyond hormonal imbalances, including psychological factors, relationship issues, medications, and chronic health conditions 5, 6

Monitoring Parameters During Treatment

If testosterone therapy is initiated:

• Monitor total testosterone levels every 6-12 months 1
• Monitor hematocrit (discontinue therapy if exceeds 54%) 1
• Monitor PSA (consider biopsy if >4.0 ng/mL or increases >1.0 ng/mL/year) 1
• Reassess symptoms after 3-6 months of therapy 1

This comprehensive laboratory evaluation provides the foundation for appropriate diagnosis and management of patients with low libido, addressing the underlying hormonal factors that may contribute to this condition.