Free and bioavaible testosterone charts

[Testocyp]

Free & Bioavailable Testosterone Calculator

Looking at the chart for 20-30 years old. The reference range for bioavaible T is 83-257ng/dL, for free T it’s 5.25-20.7ng/dL. Translated that means a man in his twenties with a total testosterone of only 187 ng/dL (6.5 nmol/L) and 30 nmol/L SHBG is still within reference for bioavaible T (87ng/dL) however for free T he’s below reference (3.7ng/dL).

Let’s take another example, total T 778 ng/dL (27 nmol/L) 30 nmol/L SHBG gives 18ng/dL free T, which is within reference at the higher end for free T, but gives 438 ng/dL bioavaible T which is way above reference. If we increase albumin from 4.3 to 4.6 g/dL, free T decrease to 17ng/dL and bioavaible increase to 448ng/dL.

”Abnormally increased testosterone values may be caused by testicular or adrenal tumors or androgen abuse when levels exceed the upper limit of normal by more than 50%.”

For bioavaible T 448 ng/dL exceed the upper limit of normal by more than 50%, for free T 17ng/dL is only in the higher end of the median.

1. Why doesn’t free and bioavaible T correlate?
2. Why is the reference range, especially for bioavaible T, so low?

 

[Type-IIx]

Free & Bioavailable Testosterone Calculator

Looking at the chart for 20-30 years old. The reference range for bioavaible T is 83-257ng/dL, for free T it’s 5.25-20.7ng/dL. Translated that means a man in his twenties with a total testosterone of only 187 ng/dL (6.5 nmol/L) and 30 nmol/L SHBG is still within reference for bioavaible T (87ng/dL) however for free T he’s below reference (3.7ng/dL).

Let’s take another example, total T 778 ng/dL (27 nmol/L) 30 nmol/L SHBG gives 18ng/dL free T, which is within reference at the higher end for free T, but gives 438 ng/dL bioavaible T which is way above reference. If we increase albumin from 4.3 to 4.6 g/dL, free T decrease to 17ng/dL and bioavaible increase to 448ng/dL.

”Abnormally increased testosterone values may be caused by testicular or adrenal tumors or androgen abuse when levels exceed the upper limit of normal by more than 50%.”

For bioavaible T 448 ng/dL exceed the upper limit of normal by more than 50%, for free T 17ng/dL is only in the higher end of the median.

1. Why doesn’t free and bioavaible T correlate?
2. Why is the reference range, especially for bioavaible T, so low?

Free and bioavailable T (in non androgen using, healthy adults) are related by the Vermeulen equation.

Vermeulen equation (1971):
...in the adult man free testosterone represents 2%, albumin bound testosterone 40%, and TeBG (SHBG) bound testosterone 58%;
in adult women these values are respectively 0.9, 18, and 81%

Cₐ: concentration of albumin
κₐ: coefficient of albumin binding to T
κₐ = 3.6 * 10⁴

AT: albumin-bound T
FT: free T
AT = κₐCₐ * FT
bioavailable T = AT + FT

Yes - some weaknesses exist in the formula, e.g., due to SHBG-bound T being in part bioactive.

How can the reference ranges be low? They're based on estimates (good ones) of population-wide values.

 

[Testocyp]

Free and bioavailable T (in non androgen using, healthy adults) are related by the Vermeulen equation.

Vermeulen equation (1971):
...in the adult man free testosterone represents 2%, albumin bound testosterone 40%, and TeBG (SHBG) bound testosterone 58%;
in adult women these values are respectively 0.9, 18, and 81%

Cₐ: concentration of albumin
κₐ: coefficient of albumin binding to T
κₐ = 3.6 * 10⁴

AT: albumin-bound T
FT: free T
AT = κₐCₐ * FT
bioavailable T = AT + FT

Yes - some weaknesses exist in the formula, e.g., due to SHBG-bound T being in part bioactive.

How can the reference ranges be low? They're based on estimates (good ones) of population-wide values.

The Vermeulen formula seem to favor high total T, compared with free androgen index/FAI calculation. For example two persons, one with high T + high SHBG and another with low T + low SHBG, can have the same FAI index, but different free/bioavaible T.

However the range for bioavaible T in my example above is still way to low compared with free T?

I think the reference range should be changed to this:
Free T: 10-35ng/dL (0.35-1.2 nmol/L)
Bioavaible T: 250-870ng/dL (8.7-30nmol/L)

Now free and bioavaible T correlate with eachother and make sense to me.