What labs should be checked in a 20-year-old male presenting with low libido?

Laboratory Evaluation for Low Libido in a 20-Year-Old Male

Morning serum total testosterone level should be the primary screening test for a 20-year-old male presenting with low libido. 1

Initial Laboratory Workup

• Morning total testosterone level (8-10 AM when levels are highest) 2, 1
• Luteinizing hormone (LH) to distinguish between primary and secondary hypogonadism 1
• Follicle-stimulating hormone (FSH) to further characterize hypogonadal state 1
• Prolactin level - especially important in men with low libido even if testosterone is normal 1
• Free or bioavailable testosterone - particularly if total testosterone is borderline low 1
• Sex hormone-binding globulin (SHBG) - important for calculating free testosterone and interpreting results 1

Additional Relevant Testing

• Hemoglobin A1c or fasting glucose - to screen for diabetes, which can affect testosterone levels 2, 1
• Lipid panel - to assess cardiovascular risk factors 1
• Estradiol - particularly if breast symptoms or gynecomastia are present 2, 1

Interpretation Considerations

• Low testosterone is generally defined as <300 ng/dL, but symptoms may occur at higher levels 1
• Repeat abnormal testosterone measurements are necessary to confirm diagnosis 1
• Free testosterone measurement is crucial as normal total testosterone may mask low free testosterone due to elevated SHBG 1
• Obesity and diabetes can affect SHBG levels and testosterone measurements 1

Common Pitfalls to Avoid

1. Timing errors: Failing to measure testosterone in the morning when levels are highest can lead to falsely low results 2, 1

2. Single measurement reliance: A single abnormal testosterone level is insufficient for diagnosis; confirmation with repeat testing is essential 1

3. Missing secondary causes: Focusing only on testosterone without measuring LH, FSH, and prolactin can miss important causes of hypogonadism 2, 1

4. Overlooking free testosterone: In young men with borderline total testosterone levels, free testosterone may be more clinically relevant 1, 3

5. Ignoring metabolic factors: Failing to screen for diabetes and hyperlipidemia, which are common comorbidities that can affect sexual function 2, 1

Special Considerations for Young Adults

• Hypogonadism in young men requires thorough evaluation as it may indicate serious underlying conditions
• The Sexual Desire Inventory-2 can be useful to objectively assess libido 4
• Screening for recreational drug use and medication side effects is particularly important in this age group 2
• Consider psychological factors that may contribute to low libido in young adults 1

Remember that low libido can be primary (not associated with identifiable medical conditions) or secondary (associated with hypogonadism, hyperprolactinemia, or other medical conditions) 5, and laboratory testing is essential to distinguish between these possibilities and guide appropriate treatment.