Free Testosterone Calculator
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Free Testosterone Calculator
Calculated Free Testosterone
—
pg/mL
Understanding Free Testosterone
Testosterone, the primary male sex hormone, circulates in the bloodstream in various forms. A significant portion is bound to proteins, primarily Sex Hormone-Binding Globulin (SHBG) and albumin. A smaller, yet biologically crucial, fraction is unbound or loosely bound, referred to as free testosterone. It is this free testosterone that is readily available for tissues to use, making it a more direct indicator of androgenic activity than total testosterone.
Measuring free testosterone can provide valuable insights into hormonal balance, especially when total testosterone levels appear within the lower end of the normal range but symptoms suggest hypogonadism. This calculator helps estimate the free testosterone level using common laboratory values.
The Calculation Formula
Several formulas exist to estimate free testosterone. A widely used method is the Vargas formula, which accounts for the binding affinity of testosterone to SHBG and albumin. The calculation typically involves these steps:
- Calculate Bound Testosterone: Determine the amount of testosterone bound to SHBG and albumin. This requires the total testosterone level, SHBG level, and albumin level. The binding affinity constants for SHBG and albumin are used here.
- Subtract Bound Testosterone from Total: The difference represents the estimated free testosterone.
The specific formula implemented in this calculator is an approximation based on established physiological models and can be represented as:
Estimated Free Testosterone (pg/mL) = [Total Testosterone (ng/dL) – (SHBG (nmol/L) * 0.357)] / (Albumin (g/dL) * 10)
Note: This formula is a simplification and may not perfectly reflect all laboratory calculation methods. The factor 0.357 converts SHBG (nmol/L) to ng/dL for testosterone binding, and the denominator (Albumin (g/dL) * 10) accounts for the concentration of albumin and its binding capacity. Units are converted to yield a result in picograms per milliliter (pg/mL).
Why Measure Free Testosterone?
- Hypogonadism Diagnosis: Essential for diagnosing conditions where the body doesn't produce enough testosterone, especially when total testosterone levels are borderline.
- Monitoring TRT: Helps physicians monitor the effectiveness of Testosterone Replacement Therapy (TRT).
- Assessing Androgenicity: Provides a clearer picture of the testosterone available for cellular action.
- Investigating Fertility Issues: Can be part of the workup for male infertility.
Disclaimer: This calculator provides an estimation for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
function calculateFreeTestosterone() {
var totalTestosterone = parseFloat(document.getElementById("totalTestosterone").value);
var shbg = parseFloat(document.getElementById("shbg").value);
var albumin = parseFloat(document.getElementById("albumin").value);
var errorMessageElement = document.getElementById("error-message");
errorMessageElement.style.display = 'none'; // Hide previous errors
// Input validation
if (isNaN(totalTestosterone) || totalTestosterone <= 0) {
errorMessageElement.innerText = "Please enter a valid Total Testosterone value (greater than 0).";
errorMessageElement.style.display = 'block';
return;
}
if (isNaN(shbg) || shbg < 0) {
errorMessageElement.innerText = "Please enter a valid SHBG value (0 or greater).";
errorMessageElement.style.display = 'block';
return;
}
if (isNaN(albumin) || albumin <= 0) {
errorMessageElement.innerText = "Please enter a valid Albumin value (greater than 0).";
errorMessageElement.style.display = 'block';
return;
}
// Constants for the formula (approximate conversion factors)
// 1 nmol/L SHBG binds roughly 0.357 ng/dL of testosterone
// Albumin binding capacity is often considered per g/dL, and we need to adjust for the total volume and binding sites.
// The denominator (Albumin * 10) is a common simplification factor to account for albumin's role relative to SHBG.
var boundTestosteroneBySHBG = shbg * 0.357; // in ng/dL
var adjustedAlbuminFactor = albumin * 10; // Approximation factor for albumin's contribution
// Ensure we don't divide by zero or a non-meaningful value
if (adjustedAlbuminFactor <= 0) {
errorMessageElement.innerText = "Albumin value results in an invalid calculation.";
errorMessageElement.style.display = 'block';
return;
}
var estimatedFreeTestosterone = (totalTestosterone – boundTestosteroneBySHBG) / adjustedAlbuminFactor;
// Ensure the result is not negative (can happen with very high SHBG relative to total T)
if (estimatedFreeTestosterone < 0) {
estimatedFreeTestosterone = 0; // Free T cannot be negative
}
// Display the result
var resultValueElement = document.getElementById("result-value");
resultValueElement.innerText = estimatedFreeTestosterone.toFixed(2); // Format to 2 decimal places
document.getElementById("result-section").style.display = 'block';
}