Free Test v. Free Test, Serum

I've been monitoring my testosterone levels for a couple years and have gone to a clinic to start TRT. My total test has been on the low range of my blood work, but my free (serum) test has always been a notch or two below the normal levels. The clinic prescribed 200mg test cyp/week, 2000iu HCG/week, and anastrazole.

Before I started, I had my PCP do another blood test. Instead of free test, serum, he did free test this time. I with this new blood work he said my free test was normal despite the serum test showing low last year. Does anyone know the difference between Free Test and Free Test, serum? Why would one be normal but one low? Should I stick with the TRT since my Free Test serum has been consistently low?

Thanks for all the help.

A bit more detail, I'm 35 and have always been active. I workout regularly but have always had trouble gaining lean mass.

My estradiol was high, too. In the 20's on the typical scale I've scene on here.