Testosterone, Free, Bioavailable and Total, MS

Bioavailable Testosterone includes free testosterone plus testosterone that is weakly bound to albumin. This fraction, like free testosterone, is considered readily available to tissues. It is calculated or measured (e.g., by precipitation method). It provides another way to assess biologically active androgen levels, often correlating well with free T and symptoms.

Free Testosterone (Calculated) is an estimate of the testosterone that is not tightly bound to proteins and is more available to tissues. It is calculated from Total Testosterone, SHBG, and Albumin rather than measured directly. This can be helpful when Total Testosterone alone does not tell the full story, especially if SHBG is unusually high or low.

Important Notes:

1. This is a calculated value, not a directly measured one.
2. It is most useful when interpreted together with Total Testosterone, SHBG, and Albumin.
3. If SHBG is very unusual or results do not match symptoms, some clinicians may prefer a non-calculated free testosterone method.

Serum Albumin is the most abundant protein in the blood, synthesized by the liver. It maintains oncotic pressure (keeping fluid in blood vessels), transports hormones, fatty acids, and drugs, and acts as an antioxidant and anti-inflammatory mediator. Low levels can indicate liver disease, kidney disease (loss in urine), malnutrition, chronic inflammation, or infection (negative acute phase reactant). High levels usually suggest dehydration.

Sex Hormone Binding Globulin (SHBG) is a protein produced mainly by the liver that binds tightly to sex hormones, primarily testosterone and estradiol, regulating their availability to tissues. High SHBG reduces free hormone levels, while low SHBG increases them. SHBG levels are influenced by factors like age, obesity, insulin resistance (lowers SHBG), thyroid function (hyper raises, hypo lowers), liver function, and estrogen levels (raises SHBG). It is essential for accurately interpreting Total Testosterone levels and calculating Free/Bioavailable Testosterone.

For males: Total Testosterone measures the overall amount of testosterone (bound and unbound) in the blood. It's the primary male sex hormone, crucial for muscle mass, bone density, libido, energy, and mood. Levels decline with age. Low levels (hypogonadism) can cause various symptoms. Optimal ranges for symptom relief and well-being are often targeted in the mid-to-upper end of the standard reference range, considering Free Testosterone as well. Important Notes:

1. Testosterone levels naturally vary by age.
2. Testosterone levels are typically highest in the morning (e.g., 8-10 AM), and reference ranges are usually based on morning samples. Levels measured later in the day may be lower.
3. Consider measuring Free Testosterone, SHBG, and Albumin for a more complete picture, especially if Total T is borderline or symptoms are present despite normal Total T.

For females: Total Testosterone measures the overall amount of testosterone (bound and unbound) in the blood. It plays a role in sexual desire/arousal, energy, mood, and helps support muscle and bone. Levels vary across the menstrual cycle and tend to decline with age. Elevated levels (hyperandrogenism) are more commonly the clinical issue in women and should be evaluated promptly.