![](https://www.endotext.org/wp-content/uploads/2020/02/etx-male-ch4-fig6.png)
Figure 6. Estradiol levels (±SD) in a mid-range proficiency sample (Y-05) distributed by the College of American Pathologists assayed using 15 different instruments in 1499 participating laboratories in 2018. The most frequently used (#6) was used by 341 laboratories. Mass spectrometry assays (n=11) are represented in column 4.