Testosterone deficiency, popularly known as “low Testosterone”, has entered the center stage in both the lay and medical communities. However, how is Testosterone deficiency (a.k.a. hypogonadism) diagnosed? What is the testosterone level threshold below which you can say you have low Testosterone? What are the references ranges for healthy men?
The Endocrine Society clinical practice guideline recommends making a diagnosis of Testosterone deficiency only in men with consistent symptoms and signs, who also have unequivocally low blood Testosterone levels. They recommend Testosterone therapy for men with symptomatic androgen deficiency, with the goal to improve their sexual function, sense of well-being, muscle mass and strength, and bone mineral density.
The Endocrine Society clinical practice guideline is against starting testosterone therapy in patients with:
- Prostate cancer or prostate-specific antigen (PSA) greater than 4 ng/ml or greater than 3 ng/ml in men at high risk for prostate cancer (such as African-Americans or men with first-degree relatives with prostate cancer without further urological evaluation).
- Hematocrit greater than 50%.
- Severe lower urinary tract symptoms with International Prostate Symptom Score (IPSS) above 19.
- Uncontrolled heart failure.
When Testosterone therapy is instituted, we suggest aiming at achieving Testosterone levels during treatment in the mid-normal range with any of the approved formulations, chosen on the basis of the patient’s preference, consideration of pharmacokinetics, treatment burden, and cost. Men receiving Testosterone therapy should be monitored.
The normative reference ranges for total and free Testosterone levels in healthy young men vary among assays and laboratories. While variation between laboratories for the same Testosterone assay (analytical method) is negligible, it should be noted that reference intervals for Testosterone (as well as LH and FSH) differ widely and significantly between assays.
In some laboratories, the lower limit of the normal range for total Testosterone level in healthy young men is 280–300 ng/dl (9.8–10.4 nmol/liter), and the lower limit of the normal range for free Testosterone level (measured by the equilibrium dialysis method) is 5–9 pg/ml (0.17–0.31 nmol/liter).
According to the medical guidelines, clinicians should use the lower limit of the normal range for healthy young men established in the specific assay that is used.
However, it should be noticed that many assays have established Testosterone reference ranges that were compiled from small convenience samples of subjects, and frequently used unreliable laboratory analytics based on the immunoassay technique, whose accuracy, particularly in the low range, has been questioned. Importantly, the immunoassay technique, which is the most widely used method for measuring total Testosterone levels, overestimates true levels and has very limited accuracy at levels below 300 ng/dl. Another study found that over 60% of the samples tested (with Testosterone levels within the adult male range) measured by most commercial assays had a spread of up to +/- 20% of those reported by LC-MS (liquid chromatography mass spectrometry), which is the gold standard Testosterone analytical method.
Table 1 shows reference ranges for total and free Testosterone levels, established in a large population of healthy young men aged 19-40 years and older men aged 70-89 years, using the gold standard LC-MS analytical method.
The first thing to note when comparing the reference ranges between young and older men is the dramatic decline Testosterone levels. Total Testosterone levels in older men are about 40-50% lower than that of younger men. Free Testosterone levels drop even more with age. This data confirms findings from previous studies which have shown that as men get older, levels of free (or bio-available) Testosterone decline at a faster rate than total Testosterone levels.
According to the approach used for defining reference limits for biological parameters, total and free Testosterone values below the 2.5th percentile (approximately 2 SD [standard deviations] below the mean) are deemed low. For total and free Testosterone in young men, this corresponds to 348 ng/dL and 70 pg/mL, respectively. The same applies to defining the high end of the reference limit (approximately 2 SD above the mean). For total and free Testosterone, this corresponds to 1197 ng/dL and 230 pg/mL, respectively.
As table 1 shows, the normal range for both total and free Testosterone is large, going all the way up to 1322 ng/dL in young men. This means that there is a lot of room for expression of different health outcomes when contrasting the low end with the high end of the normal range. In other words, it is very likely that being in the low end will have very different health consequences vs. being in the high end.
Symptoms
As stated by the US Endocrine Society, and also by European medical organizations, the diagnosis of Testosterone deficiency requires the presence of symptoms and signs suggestive of Testosterone. Table 2 lists symptoms and signs suggestive of androgen deficiency in men, according to the Endocrine Society.
TABLE 2. Symptoms and signs suggestive of androgen deficiency in men.
More specific symptoms and signs of low-Testosterone
- Reduced sexual desire (libido) and activity
- Decreased spontaneous erections
- Loss of body (axillary and pubic) hair, reduced shaving
- Very small or shrinking testes
- Inability to father children, low or zero sperm count
- Low bone mineral density
- Hot flushes, sweats
- Decreased energy, motivation, initiative, and self-confidence
- Feeling sad or blue, depressed mood, dysthymia
- Poor concentration and memory
- Sleep disturbance, increased sleepiness
- Mild anemia (normochromic, normocytic, in the female range)
- Reduced muscle bulk and strength
- Increased body fat, body mass index
- Diminished physical or work performance
Several questionnaires are available to help doctors make a diagnosis of Testosterone deficiency according to the current medical clinical guidelines. The Androgen Deficiency in Aging Men (ADAM) and the Aging Male Survey (AMS) questionnaires are two examples. Table 3 shows what you will get asked in the ADAM questionnaire.
Table 3: The Androgen Deficiency in Aging Males (ADAM) questionnaire.
- Do you have a decrease in libido (sex drive)?
- Do you have a lack of energy?
- Do you have a decrease in strength and ⁄ or endurance?
- Have you lost height?
- Have you noticed a decreased enjoyment of life?
- Are you sad and ⁄ or grumpy?
- Are your erections less strong?
- Have you noticed a recent deterioration in your ability to play sports?
- Are you falling asleep after dinner?
- Has there been a recent deterioration in your work performance?
While the ADAM and AMS questionnaires may be useful rough screening tools to screen for hypogonadism across the adult male lifespan, it should be noted that they (like all other questionnaires) are non-specific, i.e. lack diagnostic accuracy. In other words, a man who doesn’t fulfill the criteria can still have low Testosterone levels, and vice versa, a man who does fulfill the criteria can have Testosterone levels in the normal range. Therefore, the symptoms and signs related to lowTestosterone levels are only suggestive, not diagnostic of hypogonadism.
