One of the reasons it’s so difficult to get good studies on hormones is because of a handful of factors, but the main factor is researchers do not take into account when in a woman's menstrual cycle to get blood drawn to measure hormones. There appears to be mindsets that hormones are produced in a static manner, meaning you produce the same amount of hormones everyday of the month like in the study entitled, Pediatric reference intervals for FSH, LH, estradiol, T3, free T3, cortisol, and growth hormone on the DPC IMMULITE 1000.  The article discusses the sample collection in section 2.1 Patient Selection and Sample Collection:
“The study was conducted at Children’s National Medical Center, Washington, D.C., on routine patient serum specimens from patients age 1 day to 18 years accrued from January 2003 to June 2003. Specimens were sent to the laboratory after the test had been ordered by the physician. BD tubes were used throughout the study with the majority containing serum separator. The results were blinded by removing all patient identifiers except age, sex, and date of specimen collection. Approximately 50% of the samples were from minimally ill outpatients. Only a very few of the patients would be abnormal for any one analyte. The Hoffmann approach allows for removal of the abnormal results.”
The researchers of this study chose to use a method from 1963 called Statistics in the Practice of Medicine by Robert G. Hoffmann, PhD . This method does not take into consideration where a patient is in their monthly cycle. Most hormones are produced in a cyclic and rhythmic fashion, as is with the hormone testing in this study. If hormones are produced in varying amounts over at 28-31 day predictable stretch, then how will one know if that day was a peak day or low day for the hormones? If the day of the month of specimen collection is taken out of the equation, then the entire study is null and nothing will make any sense beyond that. How is anyone to know where the hormone tide cycle is on the day they drew the blood specimen? Don’t these professionals know how the hormones are produced?
For those seeking to optimize hormones, hormone testing taking blood serum labs on the specific day of your cycle (if you're still regularly menstruating) your provider tells you will help reduce the variables for truly consistent and accurate blood readings. Most doctors do not use blood to test for hormones because they’ve been taught to keep hormones too low to show up in blood so saliva testing is recommended. As you can see in the graph below, estrogen and progesterone have their own “Hormone Tide Cycle” and when you draw blood to measure estrogen and progesterone, your provider should be have you take your labs on either Day 13-13 or Day 21-22 of your cycle. Doctors who practice sub-optimal HRT will not know what any of this means because they don’t discuss it in most training and education a physician might get outside of med school. They certainly don’t teach it in med school.
If you’re going to a doctor who does not ask you to get your blood drawn on a particular day of your cycle, or does not use blood serum to test for most of your hormone testing, then you might want to consider finding an advanced HRT provider who’s been formally professional trained how to optimize your hormones to your "Hormone Sweet Spot"™. In their education and training, Panacea Physicians understand the significance of using blood to test for most hormones, including and especially estrogen and FSH, and more importantly, when to get blood drawn. There is not attaining the "Hormone Sweet Spot"™ using anything other than blood serum for testing most hormones.
If you’re having a hard time getting to your personal "Hormone Sweet Spot"™, click on the "Programs" link in the menu above and choose a program that's right for you.
 Soldin OP, Hoffman EG, Waring MA, Soldin SJ. Pediatric reference intervals for FSH, LH, estradiol, T3, free T3, cortisol, and growth hormone on the DPC IMMULITE 1000. Clin Chim Acta. 2005;355(1-2):205-10.
 Hoffmann RG. Statistics in the Practice of Medicine. JAMA. 1963;185(11):864–873. doi:10.1001/jama.1963.03060110068020