I’ve dug up a few references to using Free T to diagnose hypogonadism, rather than TT.
The lower bound for Free T is currently a bit of a grey area. I’ve seen numbers between 6 and 8 ng/dL (about 210 to 280 pmol/L), although there seems to be more consensus at the bottom end of the range.
Free testosterone may be a better tool to diagnose hypogonadism
That’s the conclusion of research by Dr Leen Antonio based on a European study into aging males.
She found that men with low Free T (in this case below 6.3 ng/dL / 220 pmol/L), but normal T, exhibited more symptoms than those with low TT (under 300 ng/dL / 10.5 nmol/L) and higher Free T.
The conclusion is that clinicians should be using Free T to make a diagnosis. This might explain why some people with higher TT levels can be symptomatic, whereas those with low TT might feel fine.
There’s an overview of the research at Medscape, and Endocrine Abstracts has the abstract.
The following are guidelines for diagnosing hypogonadism from Free T. Note that calculated values don’t always agree with direct measurements.
- The ISA, ISSAM, EAU, EAA and ASA recommend 65 pg/mL (226 pmol/L) is used as the lower bound for calculated free testosterone. (Source)
- The ISMH suggest that a free testosterone level of 5.2 ng/dL / 180 pmol/L is the cut-off for hypogonadism, and replacement therapy isn’t needed if it’s above 7.2 ng/dL / 250 pmol/L. (Source)
- The Endocrine Society recommendations don’t give an explicit value, but recommend using the lab’s ranges. For a direct measurement this is typically 4.9 to 8.9 ng/dL / 170 to 310 pmol/L. (Source)
- The Nebido Testosterone Management Tool recommends a calculated Free T value of 8 ng/dL / 270 pmol/L as the cut-off. This is from an article in The American Journal of Medicine. (Source)
There seem to be a few postings from people with TT some way over 300 ng/dL who are symptomatic, and so the above might give hints of where to look.
With natural [non-TRT] guys, FT is release in pulses and has a short half life. So results can be greatly affected by lab timing. Nevertheless, very low is very low. And with some guys, higher SHBG levels lead to more T+SHBG and some cases, TT can be exaggerated and misleading.
The intent of that publication may have been an attempt to deal with doctors who are blind to everything except TT. TT is very meaningful most of the time.
One needs several tools in their diagnostic tool box and need to be able to be aware of different situations. One cannot grasp and hold on to a single rule. Symptoms should drive the process and lab work confirms ones instinctive diagnosis.
And one needs to see implications of elevated estrogens, impaired hepatic estrogen clearance, liver enzymes, screening for effects of Rx and OTC on liver health and estrogen clearing. FT can be low, but that is a symptom and other aspect of lab work, patient symptoms and other health aspects can be used to find health issues that can hopefully be corrected. Thyroid problems can lead to low T problems and that can be from iodine deficiency. That seems like an obvious connection; but I never see that any guys here have ever had their doctors ask about iodized salt consumption. Doctors simply seem to not be able to look as the larger perspective. Have not seen doctors concerned with low cholesterol levels, even though cholesterol is the beginning of the steroid hormone cascade.
The problem with those guidelines is that they are [another] shallow cookie cutter approach that treats low T as the disease and leads to not looking for the the cause where low-T is the symptom. So we have methods to declare diagnosis of hypogonadism that too often leads to blindly and ineptly treating the symptom instead of trying to identify correctable causes. [An sad example of this is doctors treating iodine deficiency with Rx thyroid hormones when the problem is whats in the patient’s salt shaker.]
I misquoted the original research, it should be that free T is used as a diagnostic tool alongside TT. It might not be perfect, but it’s slightly better than the existing approach.
On a personal level it’ll be useful next time I speak to my doctor. I’m having issues with gynecomastia, and being able to suggest another possible cause.
I don’t think that doctors can be specialists in all fields, rather it’s a case that they’re a generalist, and have to know when to refer you to someone who is.