Testosterone is the most important male sex hormone and is responsible for the correct functioning of multiple body processes.

This anabolic steroid is directly involved in the development of reproductive organs in men as well as the development of secondary male sexual characteristics.

Testosterone plays an important role in the lives of women too.

Inadequate amounts of testosterone can lead to numerous health issues such as low bone density (and susceptibility to fractures), poor sex drive, and lack of concentration.

Normal testosterone levels in men are between 300 ng/dL and 1,000 ng/dL.

Normal testosterone levels in women are usually between 15 ng/dL and 70 ng/dL. This number varies depending on various factors such as the moment of the day, mood, diet, exercise level, and more.

However, certain men might have low levels of testosterone (under 350 ng/dL) and experience various symptoms such as fatigue, lack of sexual desire, and the development of male breasts (gynecomastia).

Testosterone replacement therapy might be useful for men who have low testosterone blood levels. This treatment will help to raise testosterone levels to normal values.

Inadequate amounts of testosterone can also impair muscle development and slow down one’s progress in the gym. Men usually have 40 times more testosterone than women, and it’s important to keep T levels in the normal range to ensure proper muscle growth.

Declining testosterone levels in men over 45 are common and are often the cause of erectile dysfunction (ED). Androgen deficiency, or hypogonadism, affects roughly 40% of men aged 45 or older. Two-thirds of these men present with symptoms. While some symptoms, like ED, indicate a deficiency, additional symptoms can be similar to those of other diseases, such as cardiovascular disease.

What is hypogonadism?

Male hypogonadism is a clinical syndrome that results from the failure of the testes to produce physiological levels of testosterone (androgen deficiency) and a normal number of spermatozoa due to disruption of one or more levels of the hypothalamic-pituitary-testicular (HPT) axis.

There are 3 types of hypogonadism:

Primary — testicular dysfunction leads to low levels of testosterone and high levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Secondary — dysfunction of the HPT axis results in low levels of testosterone, LH, and FSH.

Mixed — manifests a mixture of primary and secondary hypogonadism and can be observed in older men. Who should be tested for low testosterone? Very small or shrinking testes. Inability to father children, low or zero sperm count.

The more symptoms a patient has, the more likely he is to have low testosterone.

Women can be affected by testosterone levels as well. Hyperandrogenism (high testosterone in women) is characterized by excess production of androgens by the ovaries and/or the adrenal glands.

The most common clinical manifestation of hyperandrogenism is hirsutism or excessive hair growth in androgen-dependent areas of the body. Other clinical manifestations of hyperandrogenism include acne vulgaris, weight gain, menstrual irregularities, and, in some women with polycystic ovary syndrome (PCOS), acanthosis nigricans.

Measuring the testosterone level isn’t an easy task. Tests for free, bioavailable, and total testosterone are essential to help diagnose hypogonadism and rule out other conditions. For those who may be candidates for testosterone therapy, as well as for those already on therapy, testing can also help assess and monitor testosterone levels.

That’s because this hormone can be bound to certain proteins in the body and measuring it becomes very difficult when it’s outside the normal ranges.

For example, it’s relatively easy to determine the exact testosterone level of a healthy man, but not that easy if he’s hypogonadal (has low T) and his testosterone levels are dangerously low.

To measure low T concentrations in men, women, and prepuberty children, more sensitive tests are required.

Scientists and medical professionals have managed to create a couple of reliable measuring methods for testosterone.

These are called testosterone assays.

Serum testosterone assays

According to the dictionary, the word “essay” refers to the testing of a particular material, ore, or substance to find out its compounding ingredients.

Serum testosterone assay refers to accurately measuring the testosterone levels in the body of a male or female.

Accuracy is important because it directly impacts the diagnosis of a particular disease or health complication.

Endocrinology is the discipline responsible for measuring hormone levels in the body.

It encompasses a wide variety of assays that help the clinician confirm a diagnosis for a patient.

For example, testosterone assays are used to determine if a male patient has hypogonadism or not.

Hypogonadism consists of reduced gonad activity. Men diagnosed with hypogonadism usually have low testosterone levels and experience different symptoms such as low sex drive and gynecomastia (man boobs).

Testosterone assays are also used to determine if certain boys have delayed puberty onset and to diagnose androgen deficiency.

When circulating testosterone levels are very low, the sensitivity of some assays is diminished. That’s why it is necessary to pick the right testosterone assay to accurately determine circulating T levels.

Types of testosterone fractions in the blood

The majority of circulating testosterone in the bloodstream is bound to SHBG which is the sex hormone-binding globulin. Testosterone can also be weakly bound to albumin which is a water-soluble protein.

The albumin-bound testosterone combined with free testosterone makes up for approximately 35% of total testosterone levels.

This is also known to be bioavailable testosterone.

Hyperthyroidism and other factors that influence SHBG can lead to changes in the amount of biologically active free testosterone.

Types of testosterone tests

Measuring the testosterone levels in one’s body is not that easy.

One way to do that is by using Isotope dilution mass spectrometry. This assay measures total testosterone levels.

Laboratories also use direct chemiluminescent immunoassays. However, these assays are less accurate when testosterone concentrations are too low.

Liquid chromatography-tandem MS (mass spectrometry) is also used as well as gas chromatography-MS for more accurate results, particularly when testosterone levels are at the low and high extremes.

Measuring free testosterone is done after it has been separated from the protein-bound forms.

This can be done using equilibrium dialysis or ultracentrifugation.

Equilibrium dialysis is the most common method, and it involves introducing testosterone isotopes into a patient sample.

The free testosterone concentration is estimated based on the distribution of isotopes in the dialysis membrane.

Measuring the bioavailable testosterone can be done using ammonium sulfate which influences the testosterone bound to SHBG.

Assessing testosterone levels began approximately 30 years ago.

Tests were done on small samples of blood, but their accuracy was somehow limited.

Modern testosterone assays are more sensitive, require a smaller sample of serum, and are more affordable. They can be done using nonradioactive methods in reference labs.

How is testosterone level measured?

Up to 98% of the testosterone which can be found in the bloodstream is bound to proteins such as albumin and SHBG. Just about 2% is free.

Albumin-bound testosterone and free testosterone are known as bioavailable, and they can easily be used by tissues for androgen action.

On the other hand, total testosterone can be measured using nonradioactive immunoassay and chemiluminescent detection.

These methods offer accurate results if the male patient has testosterone levels in the normal range such as 300-1000 ng/dL.

However, these assays recorded low limits of testosterone of approximately 132 ng/dL which is not normal in healthy men.

Clinicians have wondered why this happens and how they can improve the accuracy of testosterone assays when T concentrations are very low.

When it comes to total testosterone assays, the gold standard is a steroid-free serum interacting with gravimetrically-determined amounts of testosterone.

Independent measuring methods are also used such as liquid or gas chromatography with mass spectrometry.

For women, highly sensitive tests are necessary to determine total and free testosterone levels because women have much lower amounts of testosterone in the bloodstream in comparison with men.

4 Types of Testosterone Tests You Can Buy Today

There are four different testosterone assays you can choose from to accurately determine the amount of testosterone in your bloodstream.

#1 – Testosterone Total and Free (Regular)

This test is ideal for people who have testosterone levels in the normal range.

It measures total and free testosterone using direct analog/radioimmunoassay (for free T) and electrochemiluminescence immunoassay (for total T).

On the other hand, if you know you have very low testosterone levels (you have hypogonadism and testosterone levels below 150 ng/dL) or you have very high testosterone levels (you are a bodybuilder with T levels over 1500 ng/dL) then you might want to use the LC/MS test because it’s more accurate.

If your testosterone levels are very high, the test will show above 1500 ng/dL, not the exact number (such as 1,700 or 1,800).

#2 – Testosterone Free and Weakly Bound (Bioavailable Testosterone)

Bioavailable testosterone can be used for steroid-receptor interaction.

This test measures the amount of free testosterone and weakly bound testosterone in the bloodstream.

The test doesn’t look at the testosterone bound to SHBG because this type is biologically inactive as it has a high binding affinity.

On the other hand, weakly bound testosterone is usually derived from albumin, and it has a low affinity which means that it can quickly dissociate and become available for interaction.

#3 – Testosterone, Free, Bioavailable, and Total, LC/MS (No Upper Limit)

This test doesn’t have any upper limit for either type of testosterone such as free, total, and bioavailable.

It uses more complex measuring assays such as liquid chromatography-tandem mass spectrometry to accurately determine testosterone levels.

However, this test is more suitable for bodybuilders who are known to have very high testosterone levels.

If you are not into bodybuilding or you think you have below-normal testosterone levels then this test is not ideal for you.

There are other tests that are more economical and can be used to determine your testosterone levels more accurately.

If you are on testosterone replacement therapy, you might want to choose a test that has no upper limit on total testosterone and up to 50 ng/dL limit on free testosterone.

An even more affordable test for people on testosterone replacement therapy has an upper limit of 1,500 ng/dL on total testosterone and a 50 ng/dL limit on free testosterone.

#4 – Testosterone, Total, LC/MS (No Upper Limit)

If your testosterone levels are very low (both men and women) then this test is ideal for you. It is also good for those with high testosterone due to TRT or bodybuilding. This test measures only total testosterone by liquid chromatography/ mass spectrometry.

The test is the most accurate for testosterone concentrations under 150 ng/dL or above 1500 ng/dL for total testosterone.

Why should you test your testosterone levels?

Measuring testosterone levels becomes increasingly popular nowadays, thanks to direct-to-consumer labs that are affordable and easy to use.

Males and females alike can buy one of the tests described above and determine the actual amounts of testosterone in their bloodstream.

But why is this a good idea?

First of all, if you have common testosterone deficiency symptoms such as fatigue or low sex drive then measuring your testosterone levels is highly recommended.

This will help you decide if indeed a lack of testosterone is the problem and whether you should try testosterone replacement therapy or not.

Testosterone tests give you a broader insight when it comes to your hormonal health.

Secondly, if you’re on testosterone replacement therapy already, the results of the test might provide good feedback on your progress.

The clinicians who conduct these tests can give you useful pieces of advice such as how often to take testosterone gels or injections, whether you should reduce or increase the dosage, etc.

If you’re a bodybuilder, keeping your testosterone levels in check also helps you monitor your progress.

After all, testosterone is vital for muscle development, and if you have sufficient amounts of it, you’ll ensure muscle growth in the long run.

Testosterone is important for women too. This hormone is linked to mental alertness, good mood, and increased sex drive.

Testosterone deficiency in women can also lead to low productivity at work and poor physical performance while in the gym.

Numerous advancements in the medical field coupled with improved testing devices make measuring testosterone levels a more affordable and accurate process.

For any additional questions, get in touch with our team of qualified doctors.