FP12-6 Obesity Has a Greater Influence Than Aging On Serum SHBG and Total Testosterone (TT) in Men, and a Normal TT Is Sufficient to Exclude Biochemical Hypogonadism in Older, Obese Men

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: FP12-Reproductive Hormones: Vital Effects Evidenced In Human Cohorts & Experimental Models
Saturday, June 15, 2013: 11:00 AM-11:30 AM
Presentation Start Time: 11:25 AM
Room 102 (Moscone Center)

Poster Board SAT-554
Lori Ann Cooper*1, Stephanie T Page1, Thomas James Walsh1, John Kenneth Amory2, Bradley David Anawalt1 and Alvin M Matsumoto3
1University of Washington, Seattle, WA, 2Univ of WA Med Ctr, Seattle, WA, 3VA Puget Sound Hlth Care Sys, Seattle, WA
Background: Sex hormone binding globulin (SHBG) is affected by many conditions, most notably obesity and aging.  Circulating testosterone (T) is mostly bound to SHBG and albumin; only 1-2% is unbound or “free”.  Alterations in SHBG affect total T (TT), but not free T levels.  Increasing age is associated with higher SHBG levels, whereas obesity is associated with lower SHBG levels.  It is not clear whether older, obese men have higher, lower, or similar SHBG levels compared to non-obese, younger men. 

Hypothesis: We hypothesized that increasing age is associated with a relatively greater effect on SHBG and TT levels than obesity.  We also tested whether TT is an insensitive test of biochemical hypogonadism in obese and non-obese older men.

Methods: Using a cohort of 3671 men evaluated for hypogonadism at the VA Puget Sound from 1997-2007, we compared TT, calculated free T, and SHBG among subgroups of younger and older (age <65 or ≥65 years old) and non-obese and obese (body mass index, BMI <30 or ≥30 kg/m2).  We also calculated the sensitivity of various TT thresholds for these groups to exclude biochemical hypogonadism (calculated free T <34 pg/mL).

Results: SHBG levels were higher in older men than in younger men (49 ±24 [mean±SD] vs 42 ±27 nmol/L, p<0.001).  SHBG levels were lower in obese men than in non-obese men (36 ±22 vs 50 ±27 nmol/L, p<0.001).  Differences in TT were similar to those for SHBG.  The differences in SHBG and TT associated with obesity were proportionately greater than those associated with older age.  In addition, in obese men ≥65, a TT value ≥280 ng/dL had a sensitivity of 100% to exclude biochemical hypogonadism (i.e. all had normal calculated free T levels).  A sensitivity ≥98% was not seen in the younger (non-obese and obese) and older non-obese subgroups until TT ≥400 ng/dL.  In all groups, the ability to rule in biochemical hypogonadism was poor, and a specificity of 98% was not reached until TT<150 ng/dL.

Summary: 1) Obesity has a significantly greater effect on SHBG and TT levels than aging.  2) A TT ≥280 ng/dL is highly sensitive to exclude biochemical hypogonadism in older obese men, but is insensitive in younger (non-obese and obese) and older non-obese men.

Conclusions: In older obese patients, a normal TT level (≥280 ng/dL) reliably excludes biochemical hypogonadism, but TT is a poor screening test for biochemical hypogonadism in younger (non-obese and obese) men and for non-obese older men.

Disclosure: AMM: Investigator, Abbott Laboratories, Investigator, GlaxoSmithKline, Consultant, Lilly USA, LLC, Consultant, GTx, Editor, Up To Date, Grant Review Panel, Partnership for Clean Competition. Nothing to Disclose: LAC, STP, TJW, JKA, BDA

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: Department of Veterans Affairs; NIH T32 (5T32HL007028-35); NIA RO1- AG037603 awarded to STP.
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