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J Clin Endocrinol Metab. 2015 Sep;100(9):3280-7. doi: 10.1210/JC.2015-1542. Epub 2015 Jun 29.

Serum Testosterone (T) Level Variability in T Gel-Treated Older Hypogonadal Men: Treatment Monitoring Implications.

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Division of Endocrinology (R.S.S., Y.P., C.W., P.Y.L., P.S.), Department of Medicine, and the Clinical and Translational Science Institute (Y.P., C.W.), Harbor-UCLA Medical Center and Los Angeles Biomedical Research Institute, Torrance, California 90509; The Research Program in Men's Health: Aging and Metabolism (S.B.), Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115; Yale University (T.M.G.), New Haven, Connecticut 06510; Division of Gerontology and Geriatric Medicine (A.M.M.), Department of Medicine, University of Washington, and Geriatric Research, Education, and Clinical Center, Veterans Affairs Puget Sound Health Care System (A.M.M.), Seattle, Washington 98108; Department of Aging and Geriatric Research (M.P.), University of Florida, Gainesville, Florida 32611; and Division of Endocrinology (P.J.S.), Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-5160.



The optimal frequency for on-treatment serum T measurement used for dose adjustment after transdermal T gel application is unknown, especially in older men with thinner skin and slower metabolic clearance.


The objectives of the study was to determine the variability of postgel application serum T concentrations and assess whether single levels are reflective of average serum T concentrations over 24 hours (Cavg0-24).


This was a double-blinded, placebo-controlled randomized trial.


The study was conducted at five academic centers.


Forty-seven symptomatic men 65 years old or older with an average of two morning T concentration less than 275 ng/dL participated in the study.


Transdermal T or placebo gel was applied for 120 ± 14 days. Monthly dose adjustments were made if necessary to target serum T between 400 and 500 to 800 ng/dL.


Variability of serum T 2 hours after the gel application on two outpatient visits and at multiple time points over 24 hours during the inpatient day was measured.


On-treatment T levels varied substantially on the 2 ambulatory days and over 24 hours during the inpatient day. Ambulatory 2-hour postapplication T levels did not correlate significantly with either 2-hour postapplication serum T or Cavg0-24 measured during the inpatient day. Only 22.2% of men receiving T had a Cavg0-24 within the target range of 500-800 ng/dL; 81.5% had a Cavg0-24 within the broader 300-1000 ng/dL range.


Large within-individual variations in serum T after T gel application render ambulatory 2-hour postapplication T level a poor indicator of average serum T on another day. Our data point out the limitations of dose adjustments based on a single postapplication serum T measurement.

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