Calculation of bioavailable and free testosterone in men: a comparison of 5 published algorithms.
BACKGROUND
Estimation of serum concentrations of free testosterone (FT) and bioavailable testosterone (bioT) by calculation is an inexpensive and uncomplicated method. We compared results obtained with 5 different algorithms.


METHODS
We used 5 different published algorithms [described by Sodergard et al. (bioTS and FTS), Vermeulen et al. (bioTV and FTV), Emadi-Konjin et al. (bioTE), Morris et al. (bioTM), and Ly et al. (FTL)] to estimate bioT and FT concentrations in samples obtained from 399 independently living men (ages 40-80 years) participating in a cross-sectional, single-center study.


RESULTS
Mean bioT was highest for bioTS (10.4 nmol/L) and lowest for bioT(E) (3.87 nmol/L). Mean FT was highest for FTS (0.41 nmol/L), followed by FTV (0.35 nmol/L), and FTL (0.29 nmol/L). For bioT concentrations, the Pearson correlation coefficient was highest for the association between bioTS and bioTV (r = 0.98) and lowest between bioTM and bioTE (r = 0.66). FTL was significantly associated with both FTS (r = 0.96) and FTV (r = 0.88). The Pearson correlation coefficient for the association between FTL and bioTM almost reached 1.0. Bland-Altman analysis showed large differences between the results of different algorithms. BioTM, bioTE, bioTV, and FTL were all significantly associated with sex hormone binding globulin (SHBG) concentrations.


CONCLUSIONS
Algorithms to calculate FT and bioT must be revalidated in the local setting, otherwise over- or underestimation of FT and bioT concentrations can occur. Additionally, confounding of the results by SHBG concentrations may be introduced.
de Ronde
Willem
W
Department of Endocrinology, Vrije Universiteit Medical Center, Amsterdam, The Netherlands. p.deronde@vumc.nl
van der Schouw
Yvonne T
YT
Pols
Huibert A P
HA
Gooren
Louis J G
LJ
Muller
Majon
M
Grobbee
Diederick E
DE
de Jong
Frank H
FH
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002352:Carrier Proteins / Q000378:metabolism*; D003430:Cross-Sectional Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D012709:Serum Albumin / Q000378:metabolism*; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood* / Q000378:metabolism
D002352:Carrier Proteins; D012709:Serum Albumin; D012738:Sex Hormone-Binding Globulin; C027091:cortisol binding globulin; D013739:Testosterone