Comparison of methods to measure low serum estradiol levels in postmenopausal women.
BACKGROUND
Accurate measurement of low serum estradiol (E(2) < 30 pg/ml or < 110 pmol/liter) is needed to study relationships between endogenous E(2) and risks of diseases in older women.


OBJECTIVE
The objective of this study was to determine whether an extraction-based (indirect) assay or a non-extraction-based (direct) assay correlates better with mass spectrometry and body mass index (BMI).


METHODS
In a pilot study of 40 postmenopausal women, endogenous E(2) measurements from three indirect and four direct assay methods and gas chromatography-tandem mass spectrometry (GC-MS/MS) were compared. A confirmatory study compared an indirect and a direct assay, selected among those in the pilot study, to GC-MS/MS; this study was conducted in 374 postmenopausal women not taking hormone therapy from the Ultra Low-dose TRansdermal estrogen Assessment (ULTRA) trial.


RESULTS
Pearson correlation coefficients among E(2) measurements by assay methods and BMI, and their confidence intervals, by bias-corrected bootstrap method, were used.


RESULTS
In the pilot study, E(2) by three indirect assays correlated better (P < 0.03) with GC-MS/MS and with BMI than measurements by four direct assays. In the confirmatory study, the indirect assay correlated better (P < 0.01) with GC-MS/MS and BMI than the direct assay. Measurements by the indirect and direct assays were overestimated, but deviations in direct assay measurements were less precise. Mean E(2) by the indirect and direct assays were higher (by 14 and 68%, respectively) and less reproducible than by GC-MS/MS.


CONCLUSIONS
Until mass spectrometry is practical for wide use, extraction-based indirect assays may be preferable for measuring low postmenopausal serum E(2).
Lee
Jennifer S
JS
San Francisco Coordinating Center, California Pacific Medical Center Research Institute, San Francisco, CA 94107, USA. catechols@gmail.com
Ettinger
Bruce
B
Stanczyk
Frank Z
FZ
Vittinghoff
Eric
E
Hanes
Vladimir
V
Cauley
Jane A
JA
Chandler
Walt
W
Settlage
Jim
J
Beattie
Mary S
MS
Folkerd
Elizabeth
E
Dowsett
Mitch
M
Grady
Deborah
D
Cummings
Steven R
SR
D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D004958:Estradiol / Q000097:blood*; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008875:Middle Aged; D010865:Pilot Projects; D017698:Postmenopause / Q000097:blood*
D004958:Estradiol