Laboratory Workup for Loss of Morning Erections
Order morning serum total testosterone (drawn between 8–10 AM) as the single mandatory endocrine test for any man presenting with loss of morning erections. 1, 2, 3
Essential Initial Laboratory Tests
The following tests should be obtained at the initial visit:
Morning total testosterone (8–10 AM draw) is required for every man with erectile dysfunction and loss of morning erections, as this presentation strongly suggests testosterone deficiency. 1, 2, 3
Fasting glucose or HbA1c should be measured to screen for diabetes mellitus, which is present in 15–27% of men with erectile dysfunction and frequently undiagnosed. 2, 3, 4
Fasting lipid panel (total cholesterol, LDL, HDL, triglycerides) is recommended because dyslipidemia is a major cardiovascular risk factor and erectile dysfunction serves as a sentinel marker for cardiovascular disease. 1, 2, 3
Interpretation and Follow-Up Testing
If testosterone is <300 ng/dL, repeat the measurement on a separate morning to confirm hypogonadism before initiating therapy. 1, 3
If confirmed testosterone deficiency exists (<300 ng/dL on two occasions), measure prolactin to exclude hyperprolactinemia (>35 ng/mL), which suppresses testosterone production and directly diminishes libido. 1, 5
If testosterone is low and prolactin is elevated, measure LH and FSH to differentiate primary from secondary hypogonadism and guide further endocrine evaluation. 6, 7
Additional Metabolic Studies
The 2022 AUA/SMSNA guideline on ejaculatory disorders recommends basic serum studies that may inform conditions predisposing to sexual dysfunction:
- Electrolytes, lipids, and glycosylated hemoglobin may identify medical conditions that predispose to neuropathy or vascular disease contributing to erectile dysfunction. 6
Clinical Context and Rationale
Loss of morning erections combined with decreased libido is one of the three most specific signs of late-onset hypogonadism and mandates immediate testosterone testing. 1
Erectile dysfunction predicts future cardiovascular events with a risk magnitude comparable to smoking or family history of myocardial infarction, making metabolic screening essential even when the primary complaint is sexual. 1, 2, 3
Testosterone deficiency is present in 18.7% of men presenting with erectile dysfunction, and low testosterone impairs response to PDE5 inhibitors. 4
Undiagnosed diabetes is found in 15% of erectile dysfunction patients, with another 12.1% having abnormal glucose tolerance, making glycemic screening critical. 2
What NOT to Order Routinely
Prolactin measurement is not indicated unless testosterone is confirmed to be low on repeat testing. 6, 7
LH, FSH, and thyroid-stimulating hormone are not first-line tests and should be reserved for cases with confirmed testosterone deficiency or specific clinical suspicion. 6, 7
Renal function testing is not mandatory for erectile dysfunction evaluation unless required by other clinical factors or comorbid conditions. 1
Critical Pitfalls to Avoid
Do not delay testosterone testing when loss of libido accompanies loss of morning erections; this combination makes testosterone deficiency highly probable and immediately treatable. 1
Do not order testosterone at random times of day; morning (8–10 AM) measurement is mandatory because testosterone levels exhibit diurnal variation. 1, 2
Do not skip cardiovascular risk assessment; erectile dysfunction is a marker for underlying vascular disease that may present 2–5 years before coronary symptoms. 1, 2, 3
Do not assume a single low testosterone confirms hypogonadism; repeat measurement is required before initiating testosterone replacement therapy. 1, 3