Since testosterone levels exhibit a circadian variation with peak levels in the morning, evidence-based guidelines recommend measuring morning total testosterone (TT) levels as the initial diagnostic test for androgen deficiency.
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However, it has been suggested that morning blood draw may not be necessary in older men due to a blunted circadian rhythm. We sought to determine whether it is possible to expand the morning sampling window for measurement of TT.
TT levels were measured in a subset of men (mean age of 61 years) participating in the 2013 Prostate Cancer Awareness Week.
TT levels measured in blood drawn from 8 to 11 AM (n = 229) differed significantly from those drawn outside this window (n = 442) (411. 7 vs 368. 3 ng/dl; p = 0. 0003). Differences in TT levels were evident across five blood draw time windows (p = < 0. 0001) and persisted after adjustment for age and BMI. TT levels in blood drawn from 2 to 5 PM (344. 3 ng/dl) and 5 to 8 PM (334. 4 ng/dl) differed significantly from that drawn from 8 to 11 AM (p < 0. 05), while TT levels from 11 AM to 2 PM (396. 5 ng/dl) and 8 PM to 8 AM (373. 4 ng/dl) did not (p = 0. 90 and 0. 73, respectively).
Based on these findings, it may be possible to expand the blood draw time window for measurement of serum TT. This community-based study was not prospectively design to determine the most appropriate blood draw window for TT measurement. Only a single TT measurement was made without consideration for day-to-day variability, and TT levels were not measured in the same men at different blood draw times.
Current medical research and opinion. 2015 Sep 11 [Epub]
E David Crawford, Wendy Poage, Allen Nyhuis, David A Price, Sherie A Dowsett, Steven Gelwicks, David Muram
a a Urologic Oncology, University of Colorado , CO , USA. , b b Prostate Conditions Education Council , Centennial , CO , USA. , c c Eli Lilly and Company , Indianapolis , IN , USA. , c c Eli Lilly and Company , Indianapolis , IN , USA. , c c Eli Lilly and Company , Indianapolis , IN , USA. , c c Eli Lilly and Company , Indianapolis , IN , USA. , c c Eli Lilly and Company , Indianapolis , IN , USA.