When should testosterone levels be retested after an initial low measurement?

When to Retest Testosterone After Initial Low Measurement

If testosterone levels are initially low, they must be repeated with a second early morning measurement on a separate occasion before confirming the diagnosis of testosterone deficiency. 1

Initial Confirmation Testing

• Obtain a second morning total testosterone measurement on a separate day to confirm the initial low result, as testosterone levels can fluctuate significantly 1, 2
• Both measurements should be drawn between 8 AM and 10 AM in a fasting state to ensure accuracy and consistency 1, 2
• Use the same laboratory and assay method for both measurements when possible to minimize variability 1
• A diagnosis of testosterone deficiency requires both measurements to be below 300 ng/dL along with consistent symptoms and signs 1

Additional Testing After Confirmation

Once two low testosterone measurements are confirmed, the following should be obtained:

• Measure serum luteinizing hormone (LH) to distinguish primary from secondary hypogonadism 1
• Measure serum prolactin if LH is low or low-normal, as this screens for hyperprolactinemia and potential pituitary pathology 1
• Consider free testosterone by equilibrium dialysis in men with borderline total testosterone or conditions affecting sex hormone-binding globulin (SHBG), such as obesity 1, 2

Important Diagnostic Considerations

• Men with total testosterone <150 ng/dL combined with low or low-normal LH should undergo pituitary MRI regardless of prolactin levels to exclude non-secreting adenomas 1
• If prolactin is elevated, repeat the measurement to ensure it wasn't spurious; persistently elevated prolactin warrants endocrinology referral 1
• Testosterone levels should be stable during testing—avoid measuring during testosterone rebound after androgen deprivation therapy or when on medications affecting testosterone (5-alpha reductase inhibitors, saw palmetto) 1

Monitoring After Treatment Initiation

Once testosterone replacement therapy is started, retest testosterone levels at 2-3 months after treatment initiation or after any dose change to ensure therapeutic levels are achieved 1

• Target mid-normal testosterone range (450-600 ng/dL) during treatment 1, 3
• For injectable testosterone, measure levels midway between injections targeting 500-600 ng/dL 1
• For transdermal preparations (gels, patches), levels can be measured at any time, though peak values occur 6-8 hours after patch application 1
• Once stable therapeutic levels are confirmed, monitor testosterone every 6-12 months 1, 3

Common Pitfalls to Avoid

• Do not diagnose testosterone deficiency based on a single low measurement—physiologic variation is substantial and requires confirmation 1, 2
• Avoid afternoon or random-time testosterone measurements for diagnosis, as levels decline throughout the day 1, 2
• Do not rely on screening questionnaires alone—they have poor specificity and sensitivity and cannot substitute for laboratory confirmation 1
• Ensure testosterone levels are not measured when serum testosterone is rebounding post-androgen deprivation therapy, as this can take a median of 16.6 weeks after stopping GnRH agonists 1