Mh. Gail et al., REPRODUCIBILITY STUDIES AND INTERLABORATORY CONCORDANCE FOR ASSAYS OFSERUM HORMONE LEVELS - ESTRONE, ESTRADIOL, ESTRONE SULFATE, AND PROGESTERONE, Cancer epidemiology, biomarkers & prevention, 5(10), 1996, pp. 835-844
We conducted studies to measure sources of assay variability for estro
ne, estradiol, estrone sulfate, and progesterone for postmenopausal wo
men (It = 5) and for women in the mid-follicular (n = 5) and mid-lutea
l (n = 5) phases of the menstrual cycle, A single blood sample from ea
ch woman was divided into 2.5-ml aliquots and stored at -70 degrees C,
and sets of two aliquots were sent at monthly intervals to each of th
ree laboratories (four for progesterone). Each aliquot was analyzed in
duplicate, Thus, within each menstrual category, we were able to esti
mate the components of variance due to variation among women, variatio
n among aliquots, variation among duplicate measurements, and variatio
n among the 4 analysis days, Using the logarithm of assay measurements
, we estimated the percentage of variance attributable to variation am
ong women in each menstrual category, 100 <(rho)over tilde>, where <(r
ho)over tilde> is the estimated intraclass correlation, For each assay
, 100 <(rho)over tilde> exceeded 90% for midfollicular and mid-luteal
women, For postmenopausal women, values of 100 <(rho)over tilde> excee
d 84% for estrone in two laboratories, Values of 100 <(rho)over tilde>
were lower for progesterone in postmenopausal women, although a value
of 84% was estimated from one laboratory, These studies indicate that
estrogen assays over a period of 3 months permit reliable comparisons
among women in a given menstrual category, Progesterone measurements
are likewise reliable for women in the mid-follicular and mid-luteal p
hases but somewhat less satisfactory for postmenopausal women, These a
ssessments of variability pertain only to laboratory techniques and do
not allow for secular variation in intra-woman hormone levels, Moreov
er, although these measurements tend to be reliable enough for making
comparisons among women, estimates of coefficients of variation for es
trogens are about 10% for mid-follicular and mid-luteal phase women an
d about 11-20% for postmenopausal women, Coefficients of variation for
progesterone are about 10% for mid-luteal, 20% for mid-follicular, an
d 30% for postmenopausal women.