Total Testosterone or Free Testosterone?

Summary and Comment |
April 12, 2012

Total Testosterone or Free Testosterone?

  1. Allan S. Brett, MD

A study illustrates the tradeoffs between these two measurements.

  1. Allan S. Brett, MD

In evaluating men with suspected hypogonadism, some clinicians start by ordering total testosterone (T) levels; others order free or bioavailable T levels, which presumably identify biochemical hypogonadism more accurately. Many factors (including obesity, drugs, comorbidities, assay variability, and time of day) affect total T levels.

In this study, Veterans Administration researchers analyzed data from 3700 men (mean age, 60; nearly half obese) in whom evaluation for hypogonadism included measurement of both total T and calculated free T levels. About 15% had low free T levels (<34 pg/mL) and thus were considered to have biochemical hypogonadism. Findings about sensitivity and specificity of total T as an indicator of biochemical hypogonadism were as follows:

  • At a cutoff of 280 ng/dL (this laboratory's lower limit of normal) total T was 91% sensitive and 74% specific; in other words, 91% of men with biochemical hypogonadism had total T levels <280 ng/dL, but 26% of men (100% minus the 74% specificity) without biochemical hypogonadism also had total T levels <280 ng/dL, and thus had false-positive results.

  • A cutoff of 150 ng/dL for total T would lower sensitivity to 59% (and many cases of hypogonadism would be missed) but would improve specificity to 99% (and false-positives would be uncommon).

  • A total T cutoff of 350 ng/dL would improve sensitivity to 97% but lower specificity to 53%.

Comment

This study provides a rough indication of the limitations of total T measurement for diagnosing hypogonadism. Levels below 150 ng/dL or above 350 ng/dL identify or exclude biochemical hypogonadism reasonably accurately. When levels fall between these thresholds, clinicians should consider measuring free T — particularly when clinical hypogonadism is strongly suspected.

Citation(s):

Reader Comments (6)

Buena Physician, Family Medicine/General Practice
Competing Interests: field_please_disclose[und][0][value]

Hey would you mind sharing which blog platform you're using? I'm planning to start my own blog soon but I'm having a difficult time choosing between BlogEngine/Wordpress/B2evolution and Drupal. The reason I ask is because your design and style seems different then most blogs and I'm looking for something unique. P.S My apologies for getting off-topic but I had to ask! http://e-pharmacist.org/cheap-pharmacy/

David George Other, Other, Electrical contractor

Is this really free with no shipping? Seems to be unreal.

r compton

Most Dr. are not aware of Free T3, Free T4, Free Testosterone.

Johann Robinson Other

my thoughts exactly. I am a patient that was diagnosed in 1997. Also, physicians also fail to disclose the Jekyll and Hyde aggression that results from the condition and the treatments.

George B Howell

I always check both ,total and free, testerone levels whick, I believe, saves time and is more confirming. I then repeat the tests, always on an early AM specimen.

Competing interests: None declared

Jeoffry B. Gordon

In hypothyroid ism , physicians are used to depending on TSH rather than T3 or T4 to define and monitor hypothyroidism. I am frustrated by all these studies focusing on testosterone levels without specifying LH, FSH, and prolactin levels. True clinical hypogonadism should change pituitary hormone levels.

Competing interests: None declared

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