Blood Test for Erectile Dysfunction: Why ED Is Often a Cardiovascular Warning Sign

Erectile dysfunction affects an estimated 4.3 million men in the UK, yet the majority treat it as a standalone sexual problem rather than the systemic health warning it frequently represents. Research published in the European Heart Journal found that ED precedes a cardiovascular event by an average of three to five years. In other words, difficulty achieving or maintaining an erection is often the earliest detectable sign that something is going wrong inside your blood vessels.

ED Is a Vascular Condition First

An erection depends on healthy blood flow. The penile arteries are roughly 1–2mm in diameter — significantly smaller than the coronary arteries (3–4mm) or carotid arteries (5–7mm). This means that the same atherosclerotic process that eventually causes heart attacks and strokes shows up in the penile arteries first, simply because they are narrower and become obstructed sooner. Studies suggest that approximately 50% of men presenting with ED have undiagnosed cardiovascular risk factors.

Key Biomarkers to Check

Testosterone

Testosterone is the primary male sex hormone and directly influences libido, arousal and erectile function. The normal reference range is 8.6–29.0 nmol/L, though many clinicians consider levels below 12 nmol/L as suboptimal in the context of symptoms. Low testosterone (hypogonadism) affects an estimated 2–6% of men aged 40–79 and becomes more common with age, obesity and chronic illness.

Lipid Panel (Total Cholesterol, LDL, HDL, Triglycerides)

Elevated LDL cholesterol and triglycerides promote plaque formation in arterial walls — the same process responsible for restricting blood flow to the penis. The NHS recommends total cholesterol below 5.0 mmol/L and LDL below 3.0 mmol/L. An unfavourable lipid profile in a man with ED is a strong indicator that cardiovascular screening should be prioritised.

HbA1c (Glycated Haemoglobin)

Diabetes is one of the strongest independent risk factors for ED, with diabetic men three times more likely to develop erectile problems. HbA1c reflects average blood sugar over the preceding 8–12 weeks. A result between 42–47 mmol/mol indicates pre-diabetes; 48 mmol/mol or above confirms diabetes. In the UK, approximately 4.9 million people have diabetes, and an estimated 1.1 million more are undiagnosed — many of whom present with ED before receiving a diabetes diagnosis.

Thyroid Function (TSH, Free T4)

Both hypothyroidism and hyperthyroidism can impair erectile function. Hypothyroidism reduces testosterone levels and slows metabolic processes, while hyperthyroidism can cause premature ejaculation and anxiety-related erectile difficulty. TSH outside the 0.27–4.2 mIU/L range warrants further investigation.

Prolactin

Elevated prolactin suppresses gonadotropin-releasing hormone, which reduces testosterone production. Hyperprolactinaemia (prolactin above 400 mIU/L in men) can cause ED, reduced libido and, in some cases, gynaecomastia. Causes include certain medications, pituitary tumours and chronic kidney disease.

SHBG and Free Androgen Index

SHBG binds testosterone and makes it unavailable. Even with a normal total testosterone, elevated SHBG (above 50 nmol/L) can result in low free testosterone and symptomatic hypogonadism. The Free Androgen Index (FAI) provides a more clinically useful picture of testosterone availability.

Beyond the Blood Test

If your blood work reveals cardiovascular risk factors — elevated cholesterol, raised HbA1c, or a combination — this should prompt a broader cardiovascular assessment. The connection between ED and future cardiac events is well-established enough that the European Association of Urology guidelines recommend cardiovascular screening for all men presenting with ED who do not have a clear alternative cause.

Lifestyle Factors That Show Up in Blood Work

Several modifiable risk factors that contribute to ED are directly measurable through blood testing:

• Obesity: Excess body fat increases SHBG and oestrogen while reducing testosterone. HbA1c and lipid panels reveal metabolic impact.
• Alcohol excess: Liver function markers (GGT, ALT) often indicate harmful drinking patterns that suppress testosterone.
• Sedentary lifestyle: Poor lipid profiles and elevated inflammatory markers (CRP) correlate with reduced physical activity.
• Smoking: While not directly measurable, its effects on cholesterol oxidation and vascular inflammation are visible in blood work.

Recommended Blood Tests

The Male Hormones Clarity 14 blood test (£110) covers testosterone, SHBG, FAI, prolactin, oestradiol, thyroid function and a full blood count — the essential hormonal panel for investigating ED. To assess the cardiovascular dimension, add the Cardiovascular Health blood test (£83), which includes a full lipid panel, HbA1c, CRP, and liver and kidney function markers.

The Bottom Line

Reaching for a PDE5 inhibitor without investigating the underlying cause of ED is like silencing a fire alarm without checking for smoke. A blood test can reveal whether your erectile dysfunction is being driven by low testosterone, undiagnosed diabetes, cardiovascular disease or hormonal imbalance — all of which are treatable conditions when caught early.