Erectile Dysfunction: Which Blood Tests Should You Get?

Erectile dysfunction (ED) — defined as the consistent inability to achieve or maintain an erection sufficient for satisfactory sexual activity — affects an estimated 30 million American men, with prevalence rising sharply with age (about 40% of men by age 40, 70% by age 70 experience some degree of ED). What most men (and many doctors) don't appreciate: ED is rarely a stand-alone "sexual health" issue. It's frequently the first visible symptom of an underlying medical condition that warrants attention beyond just the symptom.

The reason: erection depends on healthy blood vessels, healthy nerves, balanced hormones, and adequate blood flow. The penile arteries are smaller than the coronary arteries that supply the heart, meaning vascular damage shows up there FIRST. Research consistently shows that ED precedes cardiovascular events by 3-5 years on average — making it a meaningful early warning sign that's worth investigating, not just medicating away.

The major medical contributors to ED:

• Cardiovascular disease — the strongest medical association. Endothelial dysfunction, atherosclerosis, and reduced blood flow affect the penile arteries before larger vessels. ED + age 40+ should always prompt cardiovascular evaluation.
• Low testosterone — affects libido, erection quality, and morning erections. Testosterone declines gradually from the 30s onward and can drop below symptomatic thresholds at any age.
• Diabetes / insulin resistance — both directly cause ED through nerve damage (neuropathy) and vascular damage (microangiopathy). ED occurs in 50-75% of diabetic men, often earlier in life than in non-diabetics.
• Thyroid dysfunction — both hyperthyroidism and hypothyroidism cause ED through different mechanisms (testosterone suppression, libido changes, fatigue).
• Elevated prolactin — can suppress testosterone production. Often from medications (especially antipsychotics, some antidepressants) but occasionally from pituitary tumors (prolactinomas).
• Medications — extensive list including SSRIs, beta-blockers, diuretics, opioids, and many others. Don't stop medications independently; review with prescriber.
• Lifestyle factors — smoking, alcohol use, sedentary lifestyle, sleep deprivation, sleep apnea, chronic stress.
• Psychological factors — anxiety, depression, relationship issues. Often coexist with physical contributors.

The point of bloodwork isn't to "diagnose ED" — that's a clinical diagnosis. It's to identify the underlying medical contributors so they can be treated, which often improves the ED at the source rather than just symptomatically.

Total + Free Testosterone with SHBG. The foundational hormone evaluation. Total testosterone gives the headline number; Free Testosterone reveals the bioavailable fraction your tissues can actually use; SHBG (Sex Hormone-Binding Globulin) is the binding protein that determines that ratio. About 98% of testosterone in blood is bound to SHBG and albumin and unavailable for use — so Total can look normal while Free Testosterone is low if SHBG is elevated. Reference ranges vary by lab; typical "low" is Total testosterone below 300 ng/dL on at least two morning draws. Optimal range for symptom-free function in most men is 500-800 ng/dL Total and the upper portion of Free Testosterone range.

Critical: morning draws. Testosterone peaks 7-10 AM and drops 30-50% by afternoon. Always test in the morning, ideally fasted. Two readings 2-4 weeks apart are needed before any treatment decisions.

Hemoglobin A1c + Fasting Glucose + Fasting Insulin. The Diabetes Screening Panel ($59.99) covers all three. Diabetes is a major ED cause — uncontrolled diabetes causes ED through both nerve damage and vascular damage. Pre-diabetes also matters; insulin resistance is associated with ED even when A1c is still in the "normal" range. Fasting insulin (normal 2-20 µIU/mL, optimal below 7) catches insulin resistance years before A1c becomes abnormal.

Lipid Panel + ApoB + Lp(a) + hs-CRP. The Heart Health Panel ($74.99) bundles these. Cardiovascular risk evaluation is essential for any man with ED — the penile arteries are the canary in the coal mine for atherosclerosis. Optimal: ApoB below 90 mg/dL (below 80 if higher CV risk), Lp(a) below 30 mg/dL (lifetime once test), hs-CRP below 1.0 mg/L. Abnormal cardiac markers + ED warrants cardiology evaluation and aggressive cardiovascular risk reduction.

TSH + Free T4 (Thyroid). Both hyperthyroidism (TSH below 0.5) and hypothyroidism (TSH above 4.5) cause ED. Hyperthyroidism causes through SHBG elevation (reducing bioavailable testosterone) and anxiety/sleep effects; hypothyroidism causes through testosterone suppression and fatigue. The Thyroid Complete Panel ($109.99) adds Free T3, Reverse T3, and TPO antibodies if a more complete evaluation is needed.

Prolactin. Elevated prolactin (above 20 ng/mL in men) suppresses testosterone and causes ED. Common causes: medications (antipsychotics, some antidepressants, opioids), pituitary tumors (prolactinomas — uncommon but important not to miss), severe stress, or kidney disease. Markedly elevated prolactin (above 100 ng/mL) warrants pituitary MRI through endocrinology.

Vitamin D, 25-Hydroxy. Low vitamin D is associated with low testosterone and ED in multiple studies. The mechanism is incompletely understood but vitamin D receptors are present in Leydig cells (testosterone-producing cells in the testes). Optimal range: 40-60 ng/mL.

The core workup above catches the majority of medical contributors to ED. The following additional markers are worth ordering in specific situations:

Estradiol. Yes, men need to test estradiol too. Testosterone converts to estradiol via the aromatase enzyme, and the conversion rate varies widely between men. Elevated estradiol relative to testosterone can cause water retention, mood changes, gynecomastia (breast tissue development), and contribute to ED. Standard reference range for men is typically 10-40 pg/mL. Particularly worth checking in men with elevated body fat (adipose tissue is the primary site of aromatase activity), heavy alcohol use, or who develop ED while on TRT (testosterone replacement can elevate estradiol, requiring an aromatase inhibitor in some cases).

DHEA-S. An adrenal androgen that converts to testosterone and estrogen in peripheral tissues. Low DHEA-S (especially in younger men) can contribute to overall androgen deficiency. Tends to decline steadily from the 30s onward.

Cortisol, AM. Chronic stress and HPA-axis dysfunction can suppress testosterone production through multiple mechanisms. Drawn 7-9 AM for accurate interpretation. The Men's Hormone Panel ($159.99) includes cortisol along with the rest of the hormonal markers.

Comprehensive Metabolic Panel (CMP). Liver and kidney function — both organs are critical for hormone metabolism. Liver dysfunction can elevate SHBG (reducing free testosterone); kidney dysfunction can elevate prolactin and affect drug metabolism.

Complete Blood Count (CBC). Anemia from any cause contributes to fatigue and reduced libido. Polycythemia (elevated hematocrit) can cause hyperviscosity and vascular issues; also a possible side effect to monitor if you start TRT.

Sleep evaluation (not bloodwork, worth mentioning). Obstructive sleep apnea is strongly associated with low testosterone and ED. Treatment of sleep apnea (typically with CPAP) often improves testosterone levels and ED simultaneously. If you snore, have witnessed apneas, or wake up tired despite adequate sleep duration, a sleep study is worth doing in parallel with the bloodwork.

If testosterone is low: Confirm with a second morning draw 2-4 weeks later before any treatment decisions. If consistently low (Total below 300 ng/dL with symptoms) AND no contraindications, testosterone replacement therapy (TRT) is an option. TRT improves ED in ~60% of men with low T, often within 2-3 months. Requires ongoing monitoring (hematocrit, PSA, lipid panel, sometimes estradiol). Work with a urologist or men's-health specialist — not a "low-T clinic" that prescribes without thorough workup. Consider also addressing underlying contributors to low testosterone (obesity, sleep apnea, stress, alcohol use) which can sometimes restore testosterone without TRT.

If diabetes / insulin resistance: Diabetes management dramatically improves ED in many cases over 3-12 months. Tight glycemic control, weight management, and (in some cases) metformin or GLP-1 medications. Discuss with primary care or endocrinology. Lifestyle changes that improve insulin sensitivity — resistance training, lower-carb diet, weight loss — frequently improve ED meaningfully.

If cardiovascular markers abnormal: Cardiology referral. ED + age 40+ should always trigger CV risk evaluation. Aggressive risk reduction (statin therapy if indicated, lifestyle modifications, blood pressure management) often improves ED while also reducing future cardiac event risk.

If thyroid abnormal: Endocrinology referral. Treatment of hypothyroidism (levothyroxine) or hyperthyroidism (antithyroid medications, beta-blockers) typically improves ED within 3-6 months as hormone levels normalize.

If prolactin elevated: Identify cause. Medications are the most common (review prescriptions with doctor). Moderate elevation (20-100 ng/mL) often responds to addressing underlying cause. Markedly elevated (above 100 ng/mL) warrants pituitary MRI through endocrinology to rule out prolactinoma.

If everything's normal: Consider non-bloodwork contributors. Sleep apnea (sleep study), psychological factors (sex therapist or couples counseling), medication side effects (review with prescriber), lifestyle (smoking cessation, alcohol moderation, regular exercise). PDE5 inhibitors (sildenafil/Viagra, tadalafil/Cialis) are highly effective symptomatic treatment when underlying causes have been addressed. Discuss with urology or primary care.

When to escalate: ED that doesn't respond to PDE5 inhibitors + addressed underlying contributors warrants urology evaluation. Specialist treatments include vacuum devices, penile injections (intracavernosal injection therapy), urethral suppositories (alprostadil), and (in selected cases) penile prosthetic surgery.