Calculating Free Testosterone

Discuss Calculating Free Testosterone at the Men's Health Forum; My labs came back as follows: Total T=681 E2=33 SHBG=18. Is there any way to calculate or approximate the amount ...

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Old 01-29-2006, 12:30 AM
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Default Calculating Free Testosterone

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.
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Old 01-29-2006, 12:33 AM
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What is the range for your SHBG? The lower your SHBG, the higher your FT will be.
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Old 01-29-2006, 07:21 AM
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Here is a good calculator:

http://www.issam.ch/freetesto.htm

Rgds,
Axl
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Old 01-29-2006, 07:39 AM
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Quote:
Originally Posted by Axl
Here is a good calculator:

http://www.issam.ch/freetesto.htm
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?
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Old 01-29-2006, 07:47 AM
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Old 01-29-2006, 08:07 AM
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Quote:
Originally Posted by Axl
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.
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?
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Old 01-29-2006, 08:40 AM
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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).

http://jcem.endojournals.org/cgi/con...ull/84/10/3666

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!

Rgds,
Axl
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Old 01-29-2006, 11:29 AM
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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?
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Old 01-29-2006, 11:39 AM
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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.
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Old 01-29-2006, 12:34 PM
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Quote:
Originally Posted by DavidZ
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.
Exactly. I couldn't have said it any better.

Quote:
Originally Posted by DavidZ
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?
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.
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