Patient Instructions for Testosterone Lab Testing
You must have your testosterone blood test drawn in the early morning (ideally between 7 AM and 12 PM) while fasting, and you will need to repeat this test on a separate day to confirm any abnormal results. 1
Timing Requirements
Schedule your blood draw between 7 AM and 12 PM, with early morning (before 10 AM) being optimal, as testosterone levels naturally peak during these hours and decline throughout the day. 1
Plan for two separate blood draws on different days, both in the morning, as a single low result is insufficient for diagnosis and guidelines require confirmation with a second measurement. 1
Use the same laboratory for both tests when possible, as different labs may use different measurement methods that can affect result comparability. 1
Fasting Instructions
Fast overnight before your blood draw (no food after midnight), as recent evidence shows that both glucose loads and mixed meals can transiently lower testosterone levels by 100-123 ng/dL within 20-60 minutes of eating. 2
Avoid eating breakfast before your test, as approximately 11-56% of men with normal testosterone can temporarily drop below the diagnostic threshold of 300 ng/dL after consuming food. 2
Water is permitted during the fasting period. 3
Important Context on Fasting
While one 2021 study suggested fasting may not be necessary 4, the weight of guideline evidence and more robust research supports fasting requirements 1, 2. The AUA guidelines provide strong (Grade A) recommendations for morning testing, and the 2019 study demonstrating significant post-meal testosterone suppression in healthy men provides compelling physiological rationale for fasting. 2
Common Pitfalls to Avoid
Do not schedule afternoon or evening appointments, as compliance with proper morning timing is notoriously poor—only 9% of men in one study had testing done during the recommended morning window. 5
Do not assume one test is sufficient—even if your first result is low, diagnosis requires confirmation with a second morning measurement. 1
Do not eat breakfast before the test, even if you feel the need to, as this can artificially lower your results and potentially lead to misdiagnosis. 2
What to Expect
The blood test measures total testosterone, with levels below 300 ng/dL on both tests supporting a diagnosis of testosterone deficiency (though symptoms must also be present for actual diagnosis). 1
If results are borderline or if you have conditions affecting sex hormone-binding globulin (SHBG), your doctor may order additional testing for free or bioavailable testosterone using specialized methods. 6
Laboratory certification matters—ideally, testing should be performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in a laboratory certified by the CDC's Hormone Standardization Program for most accurate results. 3