Calculating Free Testosterone

Discussion in 'Men's Health Forum' started by js21233, Jan 28, 2006.

  1. #1

    js21233 Junior Member

    My labs came back as follows: Total T=681 E2=33 SHBG=18. Is there any way to calculate or approximate the amount of free testosterone, given these results? Is 681 a sufficient T level, since the SHBG=18? I am on an hcg + Selegiline protcol?
    I appreciate any feedback anyone has to offer.
  2. #2

    SPE Junior Member

    What is the range for your SHBG? The lower your SHBG, the higher your FT will be.
  3. #3

    Axl Junior Member

  4. #4

    DavidZ Junior Member

    Nice. :)

    Doesn't he need his Albumin level in order to calculate his Free T using this calculator? Do you know why the Albumin field has default value of 4.3 g/dL in it?
  5. #5

    Axl Junior Member

    Yep, I know why. :D Just take a look at the "explanation" link.

    J Clin Endocrinol Metab 84:3666-3672, 1999 A critical evaluation of simple methods for the estimation of free testosterone in serum

    I have read the study mentioned above. Bottom line is that working with a default value of 4,3 g/dL will not screw up the end result.

    The calculator was developed by the university of Ghent, Belgium. There are one of the best experts in the world on endocrine measurements.
  6. #6

    DavidZ Junior Member

    Thanks, Axl.

    Are you saying that the blood level of Albumin doesn't significantly affect the calcultated result of Free T? If so, I don't follow the logic here because:

    Total T = Free T + Albumin-bound T (aka, "loosely bound" T) + SHBG-bound T

    So, the calculator computes Free T from the other 3 variables. It would seem to follow that a variation in one of the other 3 variables (Albumin-bound T) would have a significant impact on the calculated Free T result. Am I missing something in the logic here?
  7. #7

    Axl Junior Member

    Hi David,

    The answer to your question is in the attached study. (now how they did the research is a bit too complex for me to post in a few sentences).

    Some interesting sentences:

    The apparent free testosterone (T) concentration obtained by equilibrium dialysis (AFTC) as well as the fraction of serum T not precipitated by 50% ammonium sulfate concentration (non-SHBG-T; SHBG, sex hormone-binding globulin), often referred to as bioavailable T, appear to represent reliable indexes of biologically readily available T, but are not well suited for clinical routine, being too time consuming.

    Several other parameters have been used without complete validation, however:
    direct immunoassay of free T with a labeled T analog (aFT),
    calculation of free T (FT) from total T
    and immunoassayed SHBG concentrations (iSHBG),
    and the free androgen index (FAI = the ratio 100T/iSHBG).

    In the view of substantial discrepancies in the literature concerning the free or bioavailable T levels, we compared AFTC, FT, aFT, FAI, and non-SHBG-T levels in a large number of sera with SHBG capacities varying from low, as in hirsute women, to extremely high as in hyperthyroidism. All these indexes of bioavailable T correlated significantly with the AFTC concentration; AFTC and FT values were almost identical under all conditions studied, except during pregnancy. Values for aFT, however, were only a fraction of either AFTC or FT, the fraction varying as a function of SHBG levels. Also, the FAI/AFTC ratio varied as a function of the SHBG levels, and hence, neither aFT nor FAI is a reliable index of bioavailable T.

    Their conclusion:
    The FT value, obtained by calculation from T and SHBG as determined by immunoassay, appears to be a rapid, simple, and reliable index of bioavailable T, comparable to AFTC and suitable for clinical routine, except in pregnancy.

    I hope this will help in answering your question? I realise I did not give a directg answer to your question, but I hope the link will help you out!

  8. #8

    DavidZ Junior Member

    OK, I took the time to study the article and I think I follow what they're doing. They're saying that Albumin varies relatively little from man to man and even wide variations do not significantly impact the calculated Free T value. In other words, the error introduced by using a constant for Albumin rather than the actual value is insignificant.

    One other question. There's a warning at the bottom of the calculator page that says:

    WARNING! The calculated free and bioavailable testosterone are reliable in most clinical situations, but should not be relied upon in situations with potential massive interference by steroids binding to SHBG; e.g. in women during pregnancy, in men during treatment inducing high levels of DHT (e.g. transdermal DHT, oral testosterone) or mesterolon

    I wonder if my very small dosage of DHT cream would render the calculated value unreliable?
  9. #9

    pmgamer18 Junior Member

    Why would anyone want to calculate Free T when it is better to have a lab test it. I know the UK does not test Free T and it needs to be calculated. But here we can get Free T done. Also I here a lot about SHBG being tested here and if your have your Free T done it is not necessary. As per my Dr. so I am not saying what needs to be done just want to know.
  10. #10

    Axl Junior Member

    Exactly. I couldn't have said it any better.

    David, I ran my old lab results through the calculator to check the "calculated" results with the lab values I've gotten. They were very similar. My advice. If you have labwork with measured free T, why don't you re-check it in this calculator. If there is a big difference, you can play with the albumin values to see how much adjustment you need to make.
  11. #11

    Axl Junior Member

    Because it's cheaper and because it is as accurate as a free T lab test.

    If you have gotten your free T lab test values, you don't need SHBG to calculate your free T, that's true. But in some cases it is nice to know where your SHBG is at. In my case, my SHBG is extremely low. It's nice to now this when interpreting my free T values.
  12. #12

    js21233 Junior Member

    Hi David,
    Thanks again for replying to my email and introducing me to this very informative site. I can gain a lot of very useful knowledge here. By the way, my Albumin this time was high, 5.3 giving me a Free T of 2.51% and Bioavailable T of 71.9%. I am feeling much better, since I started TRT to combat crushing fatigue, mild depression, etc. Are these levels, by statistical analysis, considered acceptable?
  13. #13

    js21233 Junior Member

  14. #14

    DavidZ Junior Member

    You're welcome, John.

    Your numbers look very good. Most importantly, your clinical response (i.e., how you feel) is excellent.

    That's what it all about. :)
  15. #15

    Ruper Junior Member

    I guess with that low SHBG, that free T would be reasonable.

    When I put in the results of my last test with my Albumin (4.7) I get 1.43% Free T, where as from the actual bloodwork it was quoted as 0.94%. My SHGB was 50 (7-50), total T 252 (250-1100).

    Is this just because of the normal ranges for a particular lab and thus you have to normalize the numbers, or can something else effect FreeT%?

    Also, what I found interesting was that if I increase SHGB to get FreeT% of 0.94%, then the bioavalable T come out to what was quoted a 'Free T' (23.8) on the lab report. I was always a bit confused about that number, I guess it was BioT. It still doesn't add up though.


    testosterone Total 252 250-1100
    Testosterone Free 23.8 LOW 35.0-155.0
    Testosterone %Free 0.94 LOW 1.0-3.1
    SHBG 50 7-50
    Albumin 4.7 3.2-5.1
  16. #16

    seand95 Junior Member

    get some Red Kat!
  17. #17

    chap Junior Member

    I'm wondering how your libido is and how it changed on the hcg/selegeline protocal, and also what are your dosages?
  18. #18

    js21233 Junior Member

    Libido is noticeably increased; some weeks in very high gear. I just completed three months on the HCG/Selegiline protocol. Dosages are as follows: 1/4 or 1/2 inch of Selegiline, administered daily (a two-sided, plastic spoon is provided with the Selegline cream) and (20) units of HCG on a 1/2 CC, 31 gauge insulin syringe, three times per week, MWF, administered SUBQ. (Dr. Shippen typically prescribes sub-clinical doses). When mixing the HCG, he has me using only 5 cc's of the diluent, instead of utilizing the entire 10 cc's.
    I guess I was fortunate in that I responded well to this treatment. (See DavidZ part 1 of 2 primers. Perhaps you already have. He goes into depth about the HCG protocol).
    Next time I see the good Doc, I am going to inquire if I might be better off doing the HCG daily. Sorry if I became a little long-winded; I hope I answered your question(s). Best Wishes, js
    Last edited: Feb 1, 2006
  19. #19

    test247 Junior Member

    I am 28, just had my test done while I am on HRT between cycles.

    Injecting 200mg test-c a week.

    I came in with total test 856 (scale of 250-1100) and free test is 3.38% at 289 on a scale of 35-155.
    SHBG is 7 on a scale of 7-49.
  20. #20
    Michael Scally MD

    Michael Scally MD Doctor of Medicine

    856 x 3.38% = 28.9 NOT 289

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