For most men with erectile dysfunction, an early-morning total testosterone plus a fasting glucose or HbA1c and a lipid profile are the core blood tests that guide diagnosis. Abnormal results point toward endocrine or cardiometabolic causes, and a low testosterone reading should always be confirmed with a repeat morning test before anyone acts on it. Timing and assay accuracy can shift the numbers enough to change a treatment plan entirely.
TL;DR:
- A confirmed low testosterone level requires repeat testing on different mornings and may necessitate additional hormone evaluations to identify the cause.
- Blood tests for ED should be timed between 7:00 and 11:00 AM, with fasting done when necessary, to ensure accurate and comparable results.
- Abnormal lipid or glucose levels point to vascular or metabolic causes of ED that should be prioritized over hormone treatment.
- Treatment with testosterone is only justified for men with symptoms and confirmed low levels on two separate early-morning tests, with baseline and ongoing safety monitoring.
- Variability in assay methods, especially for free testosterone, means results should be interpreted cautiously and repeat testing through certified labs is advisable.
A handful of blood tests do most of the diagnostic work when a man reports erectile dysfunction, and each one answers a distinct clinical question.
Total testosterone comes first because low levels are a treatable, well-documented contributor to ED. Guidelines commonly use a total testosterone below roughly 300 ng/dL as a reasonable threshold for considering deficiency, though the diagnosis also requires matching symptoms, not just a number on a printout, according to AUA guidance on evaluating and managing ED. If the level comes back low, the next step is not a prescription. It is a repeat test on a separate morning, plus consideration of LH, FSH, prolactin and estradiol depending on the pattern.
Fasting glucose or HbA1c screens for diabetes and prediabetes, conditions that damage small blood vessels and nerves involved in erections long before a man notices classic diabetic symptoms. A clinical review of ED and cardiometabolic risk lists HbA1c or fasting glucose alongside a lipid profile as standard components of the initial workup, precisely because cardiometabolic disease so often sits underneath erectile complaints.
A lipid profile, covering total cholesterol, HDL and LDL, checks for dyslipidemia, which narrows and stiffens the arteries supplying the penis in much the same way it affects coronary arteries. Vascular ED and heart disease frequently share the same root cause, so an abnormal lipid panel is not a side note. It can be the main finding.
Beyond those three, a basic metabolic panel evaluates kidney function, and a TSH is added when thyroid disease is suspected clinically, since both under- and overactive thyroid can present with sexual dysfunction. LH, FSH, prolactin and estradiol are not routine for every patient. They are reserved for men whose total testosterone comes back low, where the pattern of these follow-up hormones distinguishes a pituitary or hypothalamic problem from a testicular one.
Tests like a full autoimmune panel, genetic testing or advanced imaging are usually unnecessary in a routine ED workup unless the history or exam points to something specific, and ordering them without a reason just adds cost and confusion.
Hormone levels move throughout the day, so when you get drawn matters almost as much as what gets drawn.
Pro Tip: Book your blood draw for the same time of day and, when possible, the same lab both times, so a repeat testosterone test is actually comparable to the first one.
Numbers only mean something in combination. A single hormone level rarely tells the whole story, but a pattern usually does.
The EAU guideline on managing erectile dysfunction frames this laboratory testing as a chance to catch modifiable conditions early, since a man’s ED symptoms are often the first visible sign of a metabolic or vascular problem that would otherwise go unnoticed for years.
Lab results only justify testosterone therapy under specific conditions, and the bar is higher than many men expect.
Testosterone therapy is appropriate for symptomatic men with testosterone confirmed low on two separate early-morning measurements, not for men whose levels sit in the normal range. Prescribing testosterone to a man with normal testosterone does not reliably improve his erectile function, and current guidance does not support that use.
Before starting therapy, AUA guidance recommends baseline hemoglobin and hematocrit along with PSA testing, plus a check of liver and kidney function. These baselines matter because testosterone therapy can raise red blood cell counts and needs a starting point for PSA to track prostate health over time.
Two separate early-morning testosterone measurements, taken on different days, is the standard clinicians use before diagnosing deficiency and considering treatment, according to AUA guidance. That two-test rule exists precisely because a single low value is common and often does not hold up on retesting.
Testosterone assays are not all built the same, and that variability can change how a result gets interpreted.
Many standard testosterone assays vary meaningfully between labs, which is why the CDC’s Hormone Standardization program certifies labs whose methods meet a consistency standard. Asking whether your lab uses a CDC HoST-certified assay is a reasonable question, especially if a borderline result is driving a treatment decision.
Free testosterone measured by standard immunoassay is particularly unreliable. When free testosterone assessment genuinely matters, a calculated free testosterone using albumin and SHBG, or equilibrium dialysis, gives a more trustworthy number.
Pro Tip: Write down the exact time of your blood draw and the lab’s name each time, since that detail makes it far easier for a clinician to judge whether a change in your numbers is real or just noise.
A virtual visit can order the same testosterone, glucose, HbA1c and lipid panels a clinic would, arrange a morning fasting draw at a partner lab, and review results in a follow-up appointment. AM Rx offers this pathway through remote video consultations, telehealth lab orders, same-day appointments and prescription delivery, with insurance handled on the platform. Findings suggesting a pituitary mass or a markedly elevated PSA still need in-person evaluation and specialist referral.
Push for targeted tests, insist on a repeat before accepting a low result, and ask your clinician about assay type and timing. Numbers guide the conversation. They should never replace it.
— Bryan
A telehealth visit for ED works best when the labs and the conversation happen together, not as two separate errands. AM Rx handles both: a video consult with a provider, lab orders for the panels covered above, and a follow-up visit to walk through what the results actually mean for your treatment.
Before your visit, have your symptom history, current medications and a window of morning availability ready for the blood draw.
Erectile dysfunction care through AM Rx starts from $20 per month. Start with a consult on the ED page and get your evaluation moving.
This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.
Sudden onset of ED, especially alongside chest pain, unexplained fatigue or vision changes, warrants prompt medical evaluation since it can signal cardiovascular or neurologic disease. ED that appears alongside new urinary symptoms, unexplained weight loss or breast changes can also point toward a hormonal or structural cause that blood tests and a clinical exam help sort out.
Yes. Vascular disease, nerve damage, medication side effects and psychological factors like performance anxiety can all cause ED without moving testosterone, glucose or lipid values outside the normal range, which is why a normal panel does not end the evaluation.
A clinician typically takes a detailed history, checks blood pressure and relevant physical findings, and orders blood work including morning total testosterone, fasting glucose or HbA1c, and a lipid profile. Depending on results, they may add LH, prolactin or a referral for vascular or psychological evaluation before recommending treatment.
There is no single treatment that fits every man, since the right approach depends on the underlying cause found through history and blood work. Oral medications are the most commonly used first-line option for men without a specific hormonal or vascular finding that needs its own treatment first.
