title: Validity of midday total testosterone levels in older men with erectile dysfunction.
abstract: OBJECTIVE
  Based on studies showing the circadian rhythmicity of testosterone the optimal time of day to draw total testosterone in men has classically been reported as between 8 and 11 a.m. However, further studies demonstrated that the testosterone circadian rhythmicity becomes blunted with age.
  
  
  METHODS
  We retrospectively reviewed the charts of 2,569 men who presented with erectile dysfunction for total testosterone and draw times. We compared the men by age group, including less than 40 years and 5-year groupings after age 40 years. Total testosterone was analyzed for variability during the most common draw time hours (7 a.m. to 2 p.m.).
  
  
  RESULTS
  Mean total testosterone at 7 to 9 a.m. and 9 a.m. to 2 p.m. clinically and statistically differed only in men younger than 40 vs 40 to 44 years old (mean difference 207 ng/dl, 95% CI 98-315, p = 0.0004 vs 149 ng/dl, 95% CI 36-262, p = 0.01). No other group showed a clinically and statistically significant difference between those periods.
  
  
  CONCLUSIONS
  Total testosterone in men with erectile dysfunction who are younger than 45 years should be drawn as close to 7 a.m. as possible because a statistically and clinically relevant decrease in testosterone will occur during the course of the day. Men older than 45 years with erectile dysfunction can have total testosterone drawn at any time before 2 p.m. without misleading results.
authors: Division of Urology, Southern Illinois University School of Medicine, Springfield, Illinois. Electronic address: rwelliver@siumed.edu.
authors: R Charles
authors: RC
authors: Welliver
authors: Springfield Clinic, Springfield, Illinois.
authors: Herbert J
authors: HJ
authors: Wiser
authors: Department of Urology, Northwestern University Feinberg School of Medicine, Chicago, Illinois.
authors: Robert E
authors: RE
authors: Brannigan
authors: Department of Urology, University of Minnesota School of Medicine and Minneapolis Veterans Affairs Healthcare System, Minneapolis, Minnesota.
authors: Kendall
authors: K
authors: Feia
authors: Glickman Urological and Kidney Institute, Cleveland Clinic Foundation, Cleveland, Ohio.
authors: Manoj
authors: M
authors: Monga
authors: Division of Urology, Southern Illinois University School of Medicine, Springfield, Illinois.
authors: Tobias S
authors: TS
authors: Köhler
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002940:Circadian Rhythm; D007172:Erectile Dysfunction / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013739:Testosterone / Q000097:blood*; D013997:Time Factors
chemical_list: D013739:Testosterone
keywords: age groups; circadian rhythm; erectile dysfunction; testis; testosterone