What laboratory tests should be ordered when evaluating for erectile dysfunction?

Laboratory Testing for Erectile Dysfunction

Morning serum total testosterone is the only mandatory laboratory test for all men presenting with erectile dysfunction, while glucose/HbA1c and lipid profile should also be ordered to identify cardiovascular risk factors and diabetes that directly impact treatment outcomes. 1

Essential Laboratory Tests

Testosterone (Required for All Patients)

• Morning serum total testosterone must be measured in all men with ED to identify testosterone deficiency, defined as total testosterone <300 ng/dL with accompanying symptoms 1, 2
• Morning timing is critical due to diurnal variation in testosterone levels 3
• Low testosterone may explain poor response to PDE5 inhibitors and requires separate management 2
• Approximately 18.7% of men presenting with ED have low testosterone 4

Metabolic Screening (Strongly Recommended)

• Fasting glucose or HbA1c should be ordered because diabetes significantly reduces PDE5 inhibitor efficacy and may present first as erectile dysfunction 2, 3, 5

  • Diabetic men respond less robustly to sildenafil, tadalafil, and vardenafil compared to non-diabetic populations 2
  • Over 52% of ED patients have elevated HbA1c 4

• Lipid profile (total cholesterol, LDL, HDL, triglycerides) is critical because ED serves as a risk marker for cardiovascular disease, with ED being as strong a predictor of future cardiac events as cigarette smoking or family history of myocardial infarction 1, 2, 3

  • Approximately 48% of ED patients have elevated cholesterol 4

Clinical Reasoning Behind Selective Testing

The AUA guideline explicitly states that "with the possible exception of glucose/hemoglobin A1c and serum lipids, no routine serum study is likely to alter ED management" 1. This reflects the evidence-based approach that most laboratory tests do not change treatment decisions, but these three tests (testosterone, glucose, lipids) identify modifiable conditions that directly affect both ED treatment success and overall mortality/morbidity.

Additional Testing Based on Clinical Context

When Specific Conditions Are Suspected

• Renal function (creatinine, eGFR) if kidney disease is suspected, as PDE5 inhibitors require dose adjustment in moderate-to-severe renal impairment 2

  • Approximately 11.9% of ED patients have renal insufficiency 4

• Liver function tests (AST, ALT) if hepatic disease is suspected, as severe liver disease contraindicates PDE5 inhibitor use 2

• Thyroid function (TSH) only if clinical signs of thyroid dysfunction are present—not routinely recommended 2, 3

  • Only 4% of ED patients have abnormal TSH 4

• Prolactin is not routinely recommended unless hypogonadism is suspected based on history or examination 3, 4

For Patients Considering Testosterone Replacement

• Prostate-specific antigen (PSA) should be obtained as a baseline measurement in patients who may receive testosterone replacement therapy 3
  • Approximately 8.3% of ED patients have elevated PSA 4

Common Pitfalls to Avoid

• Do not order extensive laboratory panels routinely—the AUA guideline emphasizes that most tests beyond testosterone, glucose, and lipids will not alter management 1

• Do not skip testosterone testing—it is the only test with a specific moderate-strength recommendation from the AUA for all ED patients 1

• Do not forget that ED is a cardiovascular risk marker—the laboratory evaluation serves dual purposes: identifying treatable causes of ED and screening for life-threatening cardiovascular disease that may warrant separate evaluation and treatment 1

• Do not order testosterone at random times of day—morning levels are required for accurate assessment 3

• Do not rely solely on laboratory testing—interpretation must occur in conjunction with thorough medical, sexual, and psychosocial history, as psychological factors may be primary or secondary contributors 1, 3