Calculated Bioavailable Testosterone

Calculated Bioavailable Testosterone Calculator

function calculateBioavailableTestosterone() { var totalTestosterone = parseFloat(document.getElementById("totalTestosterone").value); var shbg = parseFloat(document.getElementById("shbg").value); var albumin = parseFloat(document.getElementById("albumin").value); if (isNaN(totalTestosterone) || isNaN(shbg) || isNaN(albumin) || totalTestosterone < 0 || shbg < 0 || albumin < 0) { document.getElementById("result").innerHTML = "Please enter valid positive numbers for all fields."; return; } // Constants for binding affinities (Vermeulen's model or similar) // K_SHBG (affinity constant for SHBG) in L/mol var K_SHBG = 1.0e9; // K_Albumin (affinity constant for Albumin) in L/mol var K_Albumin = 6.0e3; // Molar mass of Albumin (approx. 66.5 kDa) in g/mol var M_Albumin = 66500; // Convert SHBG from nmol/L to mol/L var shbg_mol = shbg * 1e-9; // Convert Albumin from g/dL to mol/L // (g/dL * 10 dL/L) / (g/mol) = mol/L var albumin_mol = albumin * 10 / M_Albumin; // Calculate the denominator and numerator factor based on binding affinities var denominator = 1 + (shbg_mol * K_SHBG) + (albumin_mol * K_Albumin); var numerator_factor = 1 + (albumin_mol * K_Albumin); // Calculate Bioavailable Testosterone // BT = Total Testosterone * ( (1 + (Albumin_mol * K_Albumin)) / (1 + (SHBG_mol * K_SHBG) + (Albumin_mol * K_Albumin)) ) var calculatedBioavailableTestosterone = totalTestosterone * (numerator_factor / denominator); document.getElementById("result").innerHTML = "Calculated Bioavailable Testosterone: " + calculatedBioavailableTestosterone.toFixed(2) + " ng/dL"; }

Understanding Bioavailable Testosterone

Testosterone is a crucial hormone in men, playing a vital role in muscle mass, bone density, red blood cell production, libido, and overall well-being. When measuring testosterone levels, it's important to understand that not all testosterone in the bloodstream is equally active or "available" for use by the body's cells.

What is Bioavailable Testosterone?

Testosterone circulates in the blood in three main forms:

1. Free Testosterone: This is unbound testosterone, not attached to any proteins. It is the most biologically active form, readily available to tissues.
2. Albumin-Bound Testosterone: This testosterone is weakly bound to albumin, a common blood protein. It can easily dissociate from albumin and become available to cells, making it also considered "bioavailable."
3. SHBG-Bound Testosterone: This testosterone is tightly bound to Sex Hormone Binding Globulin (SHBG). This form is generally considered biologically inactive because it cannot easily detach from SHBG to enter cells.

Bioavailable Testosterone (BT) is the sum of free testosterone and albumin-bound testosterone. It represents the portion of total testosterone that is readily available for use by the body's tissues. Measuring bioavailable testosterone can provide a more accurate picture of a person's functional testosterone status than total testosterone alone, especially when SHBG levels are abnormal.

Why is it Important?

While total testosterone levels are a common initial screening, bioavailable testosterone offers a more precise assessment of androgen deficiency (low T). Symptoms of low testosterone, such as fatigue, decreased libido, erectile dysfunction, mood changes, and loss of muscle mass, are often more closely correlated with bioavailable or free testosterone levels than with total testosterone, particularly in individuals with altered SHBG levels (e.g., due to aging, obesity, thyroid disorders, or certain medications).

How is it Calculated?

Direct measurement of bioavailable testosterone is complex and not widely available in all labs. Therefore, it is often calculated using a formula that takes into account Total Testosterone, SHBG, and Albumin levels. The calculator above uses a widely accepted formula based on the law of mass action and binding affinities (often referred to as the Vermeulen method or similar). This formula estimates the bioavailable fraction of testosterone by considering how much testosterone is bound to SHBG and albumin, and how much remains free.

• Total Testosterone (TT): The total amount of testosterone in your blood.
• SHBG (Sex Hormone Binding Globulin): A protein that binds to testosterone, making it unavailable to tissues. Higher SHBG means less bioavailable testosterone.
• Albumin: Another protein that binds to testosterone, but less tightly than SHBG. Albumin-bound testosterone is considered bioavailable.

Example Calculation:

Let's use the example values provided in the calculator:

• Total Testosterone: 450 ng/dL
• SHBG: 40 nmol/L
• Albumin: 4.5 g/dL

Using the formula, the calculated bioavailable testosterone would be approximately 50.53 ng/dL. This value helps clinicians assess whether a patient's symptoms are consistent with a functional testosterone deficiency, even if their total testosterone appears to be within a "normal" range.

Disclaimer:

This calculator provides an estimate of bioavailable testosterone based on a commonly used formula. It is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider for interpretation of your lab results and for any health concerns.