TTFB Lab Test – Measures Testosterone, Total, Bioavailable, and Free in the Blood Serum
Free Testosterone Tests are used to help diagnose clinical testosterone deficiency and male endocrine disorders such as hypogonadism, ED Erectile Dysfunction, and Andropause (Low T)
3 Types of Testosterone are found in the body.
- Bound Testosterone
- Bio-Available Testosterone
- Free Testosterone
Bound Testosterone comprises about 67% of the androgen in a man’s body and is not biologically active. Bound testosterone is attached to a protein known as SHBG (Sex hormone-binding globulin) which increases as men get older.
Bio-Available Testosterone comprises about 30% of the androgen in a man’s body and is considered to be potentially bio-active or biologically available for use by a man’s body. It is not bound to SHBG, but rather loosely bound to blood serum albumin.
Free Testosterone or Unbound Testosterone comprises 2% to 4% of the androgen in a man’s body and is fully available for use by a man’s body.
Testosterone is the major androgenic hormone or male sex hormone. Known as the “hormone of desire”, it is responsible for the development of the male sex organs and secondary sexual characteristics such as deep voice, Adam’s apple, facial hair, bigger muscles and bones.
In women, its main role is as an estrogen precursor, and is produced in minute quantities in the ovaries and adrenal glands. In both genders, it also has anabolic effects, influences body composition, mood and behavior.
In men, testosterone is secreted by the testicular Leydig cells and, to a minor extent, by the adrenal cortex. When men have Low T Symptoms, a cause could be Primary Hypogonadism or secondary Hypogonadism which impacts the proper functioning of the specialized Leydig cells. During Andropause, the male menopause, Luteinizing Hormone and LSH may not be functioning as well as they have in the past so the pituitary gland doesn’t respond as it should to signal the testes to produce testosterone.
Free Testosterone declines with age. In addition to less efficient hormone signaling, aging men’s hormone receptors are also not as efficient. As men age, levels of SHBG binding proteins also increase, removing ever more Free Testosterone from the blood stream.
Testosterone production in the testes is regulated via pituitary-gonadal feedback involving luteinizing hormone (LH) and, to a lesser degree, inhibins and activins.
Most circulating testosterone is bound to sex hormone-binding globulin (SHBG), which in men also is called “testosterone-binding globulin”. A lesser fraction is albumin bound and a small proportion exists as free hormone.
In the past, many urologists and endocrinologists believed that only Free Testosterone was thought to be the biologically active component. However, Bio-Available Testosterone is weakly bound to serum albumin and dissociates freely in the capillary bed, thereby eventually becoming available for use by tissues in the body. All non-SHBG-bound testosterone is potentially bio-active, so both Bio-Available Albumin Bound and Free Testosterone are therefore considered to be “Bioavailable”.
Excess Testosterone vs Too Little Testosterone. During childhood, excessive production of testosterone induces premature puberty in boys and masculinization in girls. In adult women, excess testosterone production results in varying degrees of virilization, including excess hair – hirsutism, oily skin and acne, oligo-amenorrhea, missed periods or infertility.
Elevated Testosterone levels are usually asymptomatic in males unless excess levels are aromatized or converted to estrogen, causing side effects of estrogen dominance. High testosterone levels can cause unwanted masculine symptoms in females. The causes for elevations in testosterone can be caused by genetic conditions; adrenal conditions, testicular tumors; but the most common is abuse of testosterone drugs, anabolic steroids or gonadotrophins by athletes or body-builders.
Decreased testosterone in females causes subtle symptoms. These may include some decline in libido, changes in body composition and mood changes. In men, androgen deficiency results in partial or complete degrees of hypogonadism, primary or secondary. This is characterized by changes in male secondary sexual characteristics, reduced sex drive, sexual dysfunction, fertiltiy and reproductive function.
Hypogonadism – Primary & Secondary
Hypogonadism symptoms. The cause is either primary, secondary or tertiary pituitary/hypothalamic testicular failure. In adult men, there also is a gradual decline in natural testosterone production starting in the mid 30’s and certainly after the age of 40.
Since testosterone hormone decline is associated with a simultaneous increase of SHBG binding protein levels, bioavailable testosterone or Free Testosterone can actually decline at a greater rate than total testosterone. Despite a near normal Total testosterone lab reference value, hypogonadism symptoms may be observed which may require androgen supplementation using TRT Testosterone Replacement Therapy.
Free Testosterone vs Total Testosterone Levels
Total Testosterone Levels for Diagnosing Low T. Measurement of total testosterone using the lab test TTST / Testosterone, Total, Serum can be enough for diagnosis of Low T when the androgen level is clearly below normal lab reference values. Low Total T Levels can confirm hypogonadism when combined with non-optimal measurements of LH and follicle-stimulation hormone (FSH) (LH / Luteinizing Hormone [LH], Serum and FSH / Follicle-Stimulating Hormone [FSH], Serum.
Free Testosterone is the most important measurement. Total Testosterone tests alone may be insufficient for diagnosis of mild testosterone deficiency, especially when Free Testosterone values are borderline and SHBG blood serum levels are high.
The measurements of Free Testosterone or Bioavailable Testosterone are highly recommended in borderline situations. Bioavailable Testosterone TTBS / Testosterone, Total and Bioavailable, Serum, is the preferred lab test assay.
Testosterone Reference Values
Testosterone Lab reference values or ranges describe reference intervals for interpretation of testosterone hormone test results. Testosterone lab test values include intervals based on age and sex, and are instrumental in diagnosing Low Testosterone or Androgen deficiency in men as well as women..
Male Total Testosterone Levels
0-5 months: 75-400 ng/dL
6 months-9 years: <7-20 ng/dL
10-11 years: <7-130 ng/dL
12-13 years: <7-800 ng/dL
14 years: <7-1,200 ng/dL
15-16 years: 100-1,200 ng/dL
17-18 years: 300-1,200 ng/dL
> or =19 years: 240-950 ng/dL
I (prepubertal): <7-20
V (young adult): 300-950
Females Total Testosterone Levels
0-5 months: 20-80 ng/dL
6 months-9 years: <7-20 ng/dL
10-11 years: <7-44 ng/dL
12-16 years: <7-75 ng/dL
17-18 years: 20-75 ng/dL
> or =19 years: 8-60 ng/dL
I (prepubertal): <7-20
V (young adult): 12-60
Males Free Testosterone Levels:
20 – <25 years: 5.25-20.7 ng/dL
25 – <30 years: 5.05-19.8 ng/dL
30 – <35 years: 4.85-19.0 ng/dL
35 – <40 years: 4.65-18.1 ng/dL
40 – <45 years: 4.46-17.1 ng/dL
45 – <50 years: 4.26-16.4 ng/dL
50 – <55 years: 4.06-15.6 ng/dL
55 – <60 years: 3.87-14.7 ng/dL
60 – <65 years: 3.67-13.9 ng/dL
65 – <70 years: 3.47-13.0 ng/dL
70 – <75 years: 3.28-12.2 ng/dL
75 – <80 years: 3.08-11.3 ng/dL
80 – <85 years: 2.88-10.5 ng/dL
85 – <90 years: 2.69-9.61 ng/dL
90 – <95 years: 2.49-8.76 ng/dL
95-100+ years: 2.29-7.91 ng/dL
<1 year: Term infants
1-8 years: <0.04-0.11 ng/dL
9 years: <0.04-0.45 ng/dL
10 years: <0.04-1.26 ng/dL
11 years: <0.04-5.52 ng/dL
12 years: <0.04-9.28 ng/dL
13 years: <0.04-12.6 ng/dL
14 years: 0.48-15.3 ng/dL
15 years: 1.62-17.7 ng/dL
16 years: 2.93-19.5 ng/dL
17 years: 4.28-20.9 ng/dL
18 years: 5.40-21.8 ng/dL
19 years: 5.36-21.2 ng/dL
Females Free Testosterone Levels:
20 – <25 years: 0.06-1.08 ng/dL
25 – <30 years: 0.06-1.06 ng/dL
30 – <35 years: 0.06-1.03 ng/dL
35 – <40 years: 0.06-1.00 ng/dL
40 – <45 years: 0.06-0.98 ng/dL
45 – <50 years: 0.06-0.95 ng/dL
50 – <55 years: 0.06-0.92 ng/dL
55 – <60 years: 0.06-0.90 ng/dL
60 – <65 years: 0.06-0.87 ng/dL
65 – <70 years: 0.06-0.84 ng/dL
70 – <75 years: 0.06-0.82 ng/dL
75 – <80 years: 0.06-0.79 ng/dL
80 – <85 years: 0.06-0.76 ng/dL
85 – <90 years: 0.06-0.73 ng/dL
90 – <95 years: 0.06-0.71 ng/dL
95-100+ years: 0.06-0.68 ng/dL
<1 year: Term infants
1 to 15 days: 0.06-0.25 ng/dL*
1-4 years: <0.04 ng/dL
5 years: <0.04-0.07 ng/dL
6 years: <0.04-0.14 ng/dL
7 years: <0.04-0.23 ng/dL
8 years: <0.04-0.34 ng/dL
9 years: <0.04-0.46 ng/dL
10 years: <0.04-0.59 ng/dL
11 years: <0.04-0.72 ng/dL
12 years: <0.04-0.84 ng/dL
13 years: <0.04-0.96 ng/dL
14 years: <0.04-1.06 ng/dL
15-18 years: <0.04-1.09 ng/dL
19 years: 0.06-1.08 ng/dL
Males Bioavailable Testosterone Levels
< or =19 years: not established
20-29 years: 83-257 ng/dL
30-39 years: 72-235 ng/dL
40-49 years: 61-213 ng/dL
50-59 years: 50-190 ng/dL
60-69 years: 40-168 ng/dL
> or =70 years: not established
< or =19 years: not established
20-50 years (on oral estrogen): 0.8-4.0 ng/dL
20-50 years (not on oral estrogen): 0.8-10 ng/dL
50 years: not established
Interpretation of Testosterone Test Results
Total Testosterone Results Interpretation:
Decreased testosterone levels indicate partial or complete hypogonadism. Serum testosterone levels are usually below the reference range. The cause is either primary or secondary/tertiary (pituitary/hypothalamic) testicular failure.
Primary testicular failure is associated with increased luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels, and decreased total, bioavailable, and free testosterone levels.
Genetic causes (eg, Klinefelter syndrome, XX males)
Developmental causes (eg, testicular maldescent)
Testicular trauma or ischemia (eg, testicular torsion, surgical mishap during hernia operations)
Infections (eg, mumps)
Autoimmune diseases (eg, autoimmune polyglandular endocrine failure)
Metabolic disorders (eg, hemochromatosis, liver failure)
Secondary/tertiary hypogonadism, also known as hypogonadotrophic hypogonadism, shows low testosterone and low, or inappropriately “normal,” LH/FSH levels; causes include:
Inherited or developmental disorders of hypothalamus and pituitary (eg, Kallmann syndrome, congenital hypopituitarism)
Pituitary or hypothalamic tumors
Hyperprolactinemia of any cause
Malnutrition or excessive exercise
Medical or recreational drugs (eg, estrogens, GNRH analogs, cannabis)
Increased testosterone levels:
In prepubertal boys, increased levels of testosterone are seen in precocious puberty. Further workup is necessary to determine the causes of precocious puberty
In adult men, testicular or adrenal tumors or androgen abuse might be suspected if testosterone levels exceed the upper limit of the normal range by more than 50%.
Monitoring of Testosterone Replacement Therapy:
The aim of treatment is normalization of serum testosterone and LH. During treatment with depot-testosterone preparations such as Pfizer Cypionate Injections, trough levels of serum testosterone should still be within the normal range, while peak levels should not be significantly above the normal young adult range.
Bioavailable and Free Testosterone:
Usually, bioavailable and free testosterone levels parallel total testosterone levels. However, a number of conditions and medications are known to increase or decrease the SHBG (SHBG / Sex Hormone Binding Globulin [SHBG], Serum) concentration, which may cause total testosterone concentration to change without necessarily influencing the bioavailable or free testosterone concentration, or vice versa.
The following can effect Total and Free Testosterone levels:
Treatment with corticosteroids and sex steroids, particularly oral estrogen, can result in changes in SHBG levels and availability of sex-steroid binding sites on SHBG. This may make diagnosis of subtle testosterone abnormalities difficult.
Inherited abnormalities in SHBG binding.
Liver disease and severe systemic illness.
In pubertal boys and adult men, mild decreases of total testosterone without LH abnormalities can be associated with delayed puberty or mild hypogonadism. In this case, either bioavailable or free testosterone measurements are better indicators of mild hypogonadism than determination of total testosterone levels.
In polycystic ovarian syndrome and related conditions, there is often significant insulin resistance, which is associated with low SHBG levels. Consequently, bioavailable or free testosterone levels may be more significantly elevated.
Using Bioavailable and Free Testosterone to monitor TRT.
Free Testosterone vs Bioavailable vs Total Testosterone Testing for monitoring male hormone therapy. Either bioavailable (TTBS / Testosterone, Total and Bioavailable, Serum) or Free Testosterone Lab Test (TGRP / Testosterone Total and Free, Serum) should be used as supplemental tests to total testosterone in the above situations.
The correlation coefficient between bioavailable and free testosterone by equilibrium dialysis is 0.9606. However, bioavailable testosterone is usually the preferred test, as it more closely reflects total bioactive testosterone, particularly in older men. Older men not only have elevated SHBG levels, but albumin levels also may vary due to coexisting illnesses.
Use of Anti-Estrogens in Testosterone Therapy
Female Low Testosterone Levels:
Decreased testosterone levels may be observed in primary or secondary ovarian failure, analogous to the situation in men, alongside the more prominent changes in female hormone levels. Most women with oophorectomy have a significant decrease in testosterone levels.
Increased Female testosterone levels may be seen in:
Congenital adrenal hyperplasia: nonclassical (mild) variants may not present in childhood but during or after puberty. In addition to testosterone, multiple other androgens or androgen precursors are elevated, such as 17OH-progesterone (OHPG / 17-Hydroxyprogesterone, Serum), often to a greater degree than testosterone.
Prepubertal girls: analogous to males, but at lower levels, increased levels of testosterone are seen in precocious puberty.
Ovarian or adrenal neoplasms: high estrogen values also may be observed, and LH and FSH are low or “normal.” Testosterone-producing ovarian or adrenal neoplasms often produce total testosterone values >200 ng/dL.
Polycystic ovarian syndrome: hirsutism, acne, menstrual disturbances, insulin resistance and, frequently, obesity, form part of this syndrome. Total testosterone levels may be normal or mildly elevated and, uncommonly, >200 ng/dL.
Monitoring of Women’s Testosterone Replacement Therapy:
The efficacy of testosterone replacement in females is under study but much clinical evidence shows that testosterone supplementation can help improve libido and treat vaginal discomfort. If it is used, total testosterone levels should be kept within the normal female range at all times. Bioavailable or free testosterone levels also should be monitored to avoid overtreatment.
Monitoring of Antiandrogen Therapy:
The goal of anti-androgens in therapy is usually to suppress testosterone levels to castrate levels or below but no more than 25% of the lower reference range value.
Antiandrogen therapy is most commonly employed in the management of mild-to-moderate “idiopathic” female hyperandrogenism, as seen in polycystic ovarian syndrome. Total testosterone levels are a relatively crude guideline for therapy and can be misleading. Therefore, bioavailable or free testosterone also should be monitored to ensure treatment adequacy. However, there are no universally agreed biochemical endpoints and the primary treatment end point is the clinical response.
Testosterone Levels Fluctuate
Early morning testosterone levels in young male individuals are, on average, 50% higher than p.m. levels. Lab reference ranges are usually derived from a.m. specimens.
Testosterone levels can also fluctuate substantially between different days, and sometimes even more rapidly. Assessment of androgen status should be based on more than a single measurement.
The low end of the normal reference range for total testosterone and free testosterone can vary from lab to lab.
While free testosterone can be used for the same indications as bioavailable testosterone, determination of bioavailable testosterone levels may be superior to free testosterone measurement in most situations.