In a nutshell, if you draw a line from your total testosterone on the left side of the plot over to your SHBG on the right side of the plot, that line will intersect the central curve at your calculated free testosterone value.
I’m interested if anyone can explain why the typical lab reference ranges for free testosterone are so low compared to the values on this chart. For example, I looked at my lab work and the ranges used are 25-80 pmol/L. If I look on the nomogram above, this range is so low on the central curve it can’t be reconciled with typical total testosterone and SHBG levels.
Any insight is appreciated.
PS: The color lines all over the nomogram have nothing to do with this question. This is just the best picture of a related nomogram I happened to find.
There are several methods for measuring free testosterone. The only one that is accurate is equilibrium dialysis which is not widely available and rarely used due to its cost. If you cannot use equilibrium dialysis then calculating free testosterone from SHBG, albumin and total T is generally considered more accurate than the other measurement methods. However I am unsure exactly how accurate these equations are as I am still trying to find a paper that does a comparison.
[quote]MacJabberwock wrote:
I’m interested if anyone can explain why the typical lab reference ranges for free testosterone are so low compared to the values on this chart. For example, I looked at my lab work and the ranges used are 25-80 pmol/L. If I look on the nomogram above, this range is so low on the central curve it can’t be reconciled with typical total testosterone and SHBG levels.
[/quote]
This is a pretty interesting chart. I inputted both SHGB values with corresponding FT and it’s almost spot-on.
To answer your question, FT measured frequently in the Unites States uses the measurement pg/ml. Use this site to help you out with the calculations.
It says your lab’s FT range in ng/ml is 72-230 if my calculations are correct. Input your FT values and divide by 10 to get your levels to use on the nomogram.
I did recently read a paper that compares the (in)accuracy of the various methods. I just took a look through my browser history and didn’t immediately find it, but when/if I do I will post a link here. One thing that stood out for me is how inaccurate the equations get as SHBG gets to large values. I see this in my own measurements (I have measured values for freeT, totalT, albumin, and SHBG)
However, my question isn’t about the accuracy of the various methods, it’s about the range that appears on the nomogram versus the range that the various labs are using. Why are the lab ranges (whether calculated or measured) so low compared to the nomogram free T values?
I could also ask why the lab ranges don’t represent 1-2% of the total testosterone. For example, with total testosterone lab ranges of 7.6-31.4 nmol/L, why aren’t the lab ranges 76-628 pmol/L (assuming free T should be 1-2% of total T)? Instead as I mentioned above free T ranges are 25-80 pmol/L. I’m thinking to contact the lab directly and see if I can get a response, but was hoping someone on here could offer some rationale.
Thanks for the link. You can also convert between pmol/L and pg/mL by just reading the corresponding value right from the central curve on the nomogram, since it’s marked both in pg/mL and pmol/L.
I hate to say it but I think you made a calculation error, e.g. 25 pmol/L converts to 7.2 pg/mL = 0.0072 ng/mL, not to 72 ng/mL. 7.2 pg/mL is what my calculations give me and also what reading from the curve on the nomogram gives me. Again, my point is that this value (7.2 pg/mL or 25 pmol/L) appears way down to the lower left side of the nomogram chart, and so if you try to draw a straight line through the SHBG, FT, and total T, you’ll see that it doesn’t work out. In other words, the freeT range my lab is using is strangely low, but why?
I am not the most math savvy man on the planet. Do you have any tests where TT, FT, and SHGB were drawn together? If you do, post them and we’ll try to get to the bottom of it.
[quote]MacJabberwock wrote:
However, my question isn’t about the accuracy of the various methods, it’s about the range that appears on the nomogram versus the range that the various labs are using. Why are the lab ranges (whether calculated or measured) so low compared to the nomogram free T values?
[/quote]
Labs can have different reference ranges due to high variability between test kit manufacturers and differences in methodology for determining the reference range. Your reference range for your lab is significantly lower than that of my lab which is 130-400 pmol/L.
In my experience getting information from a lab is challenging at best but I would be interested in any response you receive. I would suggest you find contact information for the head biochemist and phone them. You should also try to determine which test manufacturer they use.
All that said I think your time is better spent on examining and acting on the results of more reliable tests considering the inaccuracy of free test measurements when not done by equilibrium dialysis.
[quote]yesnomayed wrote:
Labs can have different reference ranges due to high variability between test kit manufacturers and differences in methodology for determining the reference range. Your reference range for your lab is significantly lower than that of my lab which is 130-400 pmol/L.
In my experience getting information from a lab is challenging at best but I would be interested in any response you receive. I would suggest you find contact information for the head biochemist and phone them. You should also try to determine which test manufacturer they use.
All that said I think your time is better spent on examining and acting on the results of more reliable tests considering the inaccuracy of free test measurements when not done by equilibrium dialysis.[/quote]
I agree with your sentiment. The primary reason I am fixated on free T is that this test is the one that consistently matches my symptoms. I had freeT, bioT, TT, and SHBG tested multiple times. FreeT has consistently been at the bottom of the range. BioT is also always in the bottom third of the range.
I’m going to email the gentleman who presented these slides and see if he can shed any light on this issue:
For posterity, here is the nomogram with my most recent values plotted. The freeT reported by the lab is no where close to the intersection point of the line and the central curve. (And nothing in the lab range would be close either).
[quote]MacJabberwock wrote:
I agree with your sentiment. The primary reason I am fixated on free T is that this test is the one that consistently matches my symptoms. I had freeT, bioT, TT, and SHBG tested multiple times. FreeT has consistently been at the bottom of the range. BioT is also always in the bottom third of the range.
[/quote]
It may be worthwhile in your case to pay for equilibrium dialysis out of pocket.
Well, I emailed Gamma-Dynacare and didn’t receive a response. Meanwhile I did some reading about the various methods of measuring and calculating freeT. I am amazed at the imprecision accepted and the continued use of equations that are obviously error prone. The literature contains plenty of critiques, for example:
De Ronde et. al, “Calculation of Bioavailable and Free Testosterone in Men: A Comparison of 5 Published Algorithms”, Clinical Chemistry,52:9, 1777-1784 (2006), which concludes:
“Although these conclusions seem obvious, calculated concentrations of bioT or FT are widely described in scientific journals and probably used in clinical practice, mostly without prior in-house validation of the calculated results. Without in-house validation, the use of these algorithms is highly questionable.”
Especially if the SHBG is high, the existing equations give large relative errors in the calculated free testosterone. One paper pegged the error at up to 96% for the cases examined.
So now I am going to pay out of pocket for a proper test. I’m in Ontario, and will have to go to a US lab. I’m thinking about sending a blood sample here, if anyone can comment:
I’m still waiting on the cost. I contacted Mayo and they wouldn’t give me the cost. Instead they will only give such information to doctors and healthcare professionals.
I’ll send my blood anywhere I can get accurate results…
