What laboratory evaluations are recommended for patients presenting with erectile dysfunction?

Laboratory Evaluations for Erectile Dysfunction

Routine laboratory tests for patients with erectile dysfunction should include HbA1c, fasting blood glucose, lipid profile, and morning serum total testosterone levels. 1

Essential Laboratory Tests

• Morning Total Testosterone:

  • Must be measured in all men with ED 1
  • Should be collected in the morning when levels are highest
  • Normal range typically 300-800 ng/dL 2
  • If total testosterone is normal but ED persists, consider measuring:
    • Free or bioavailable testosterone (especially in obese patients) 2
    • Sex hormone-binding globulin (SHBG) - high SHBG is the most common cause of normal total testosterone with low free testosterone 2

• Metabolic Evaluation:

  • HbA1c 1
  • Fasting blood glucose 1
  • Lipid profile 1

Additional Testing Based on Clinical Presentation

• Hormonal Testing:

  • Luteinizing hormone (LH) - to distinguish primary from secondary hypogonadism if testosterone is low 2
  • Estradiol - if breast symptoms or gynecomastia are present 2

• Cardiovascular Risk Assessment:

  • ED is a significant risk marker for underlying cardiovascular disease 1
  • Consider cardiac risk stratification using established algorithms 1

Specialized Testing

For patients who don't respond to first-line treatments (e.g., PDE5 inhibitors), additional testing may include 1:

• Nocturnal penile tumescence
• Penile Doppler ultrasound
• Bulbo-cavernosus reflex
• Dorsal sensory nerve conduction of the penis
• Pudendal nerve SSEP
• Assessment of PGE1 effect on erection
• Psychological evaluation
• Urodynamic studies

Clinical Pearls and Pitfalls

• Timing matters: Testosterone should be measured in the morning when levels are highest to avoid false low readings 2
• Method matters: LC-MS/MS is preferred for total testosterone measurement over direct immunoassay methods due to higher sensitivity (0.88 vs 0.74) 2
• Don't miss hypogonadism: Testosterone deficiency is defined as total testosterone <300 ng/dL with presence of symptoms 1
• Medication review is crucial: Many medications can cause ED, including antihypertensives (especially thiazide diuretics and beta-blockers) and psychotherapeutic drugs (particularly SSRIs) 1
• Consider psychological factors: Even with organic causes, psychological factors often contribute to ED and may require specialized evaluation 1

Algorithmic Approach

1. Obtain comprehensive history (sexual, medical, medication, substance use)
2. Order essential labs: morning total testosterone, HbA1c, fasting glucose, lipid profile
3. If testosterone <300 ng/dL, obtain LH to determine primary vs. secondary hypogonadism
4. If normal testosterone but persistent symptoms, consider free testosterone and SHBG
5. Evaluate for cardiovascular risk factors
6. For non-responders to first-line therapy, consider specialized testing

By following this systematic approach to laboratory evaluation, clinicians can identify underlying causes of ED and develop appropriate treatment strategies that address both the symptom and any contributing medical conditions, ultimately improving patient outcomes and quality of life.