Free testosterone calculator

Quickly get calculated free testosterone and bioavailable testosterone levels, by simply entering measured values for total testosterone, SHBG and albumin (obtained from blood testing) in the fields below.

Free and bioactive testosterone levels may more accurately reflect true androgen status than total testosterone levels, especially in men with conditions that impact SHBG levels, such as advanced age and chronic diseases.1 Free testosterone can also be used to strengthen a diagnosis of hypogonadism, especially in symptomatic men who have borderline low or low-normal total testosterone levels.

Because low calculated free testosterone, even in the presence of normal total testosterone levels, can be associated with hypogonadism symptoms,2 there is clinical value of calculated free testosterone when making the diagnosis of hypogonadism and during monitoring of men who are receiving testosterone therapy. For more information, see “What is the clinical value of assessing free testosterone levels?

Using a value of 3.6 x 104 L/mol for the association constant of albumin for T, the calculated albumin-bound T varied from 7.14 nmol/L (40 g/L albumin) to 7.80 nmol/L (50 g/L albumin). In view of the relatively unimportant changes in FT, when the albumin concentration varies by as much as 25%, it was concluded that for routine purposes FT could be calculated assuming an albumin concentration of 43 g/L (6.2 x 10-4 mol/L) if one is not dealing with sera from patients with marked abnormalities in plasma protein composition, such as in nephrotic syndrome or cirrhosis of the liver, or with sera obtained during pregnancy, in which cases the actual albumin concentration should be taken into account.

* Vermeulen et al., A critical evaluation of simple methods for the estimation of free testosterone in serum, J Clin Endocrinol Metab (1999) 84(10): 3666-72

A symptomatic response to T therapy is generally seen within 3 months. Monitoring should occur at least 2-3 times during the first year, and 1-2 times per year thereafter. Monitoring should include serum T, PSA levels, and hematocrit/ hemoglobin. There is no need to measure liver or renal function tests for any of the routine T-therapy formulations.

** Traish et al., Testosterone Deficiency, The American Journal of Medicine (2011) 124, 578-587

This free testosterone calculator is based on the Vermeulen formula.3 Variation of albumin levels within the physiological range of 40-50 g/L (5.8 -7.2 x 10-4 mol/L) have a negligible impact on calculated free testosterone.

Therefore, in routine clinical practice, free testosterone can be calculated assuming an albumin concentration of 43 g/L (6.2 x 10-4 mol/L), only requiring input of measured values for total testosterone and SHBG.

However, when dealing with patients with marked abnormalities in plasma protein composition, such as in nephrotic syndrome or cirrhosis of the liver, the actual measured albumin level should be entered into the calculator.

d) A symptomatic response to T therapy is generally seen within 3 months. Monitoring should occur at least 2-3 times during the first year, and 1-2 times per year thereafter. Monitoring should include serum T, PSA levels, and hematocrit/ hemoglobin. There is no need to measure liver or renal function tests for any of the routine T-therapy formulations.

* References: Traish et al. Testosterone Deficiency, The American Journal of Medicine (2011) 124, 578-587

 

g) Using a value of 3.6 x 104 L/mol for the association constant of albumin for T, the calculated albumin-bound T varied from 7.14 nmol/L (40 g/L albumin) to 7.80 nmol/L (50 g/L albumin). In view of the relatively unimportant changes in FT, when the albumin concentration varies by as much as 25%, it was concluded that for routine purposes FT could be calculated assuming an albumin concentration of 43 g/L (6.2 x 10-4 mol/ L) if one is not dealing with sera from patients with marked abnormalities in plasma protein composition, such as in nephrotic syndrome or cirrhosis of the liver, or with sera obtained during pregnancy, in which cases the actual albumin concentration should be taken into account.

** References: Vermeulen et al., A critical evaluation of simple methods for the estimation of free testosterone in serum, J Clin Endocrinol Metab (1999) 84(10): 3666-72

Using a value of 3.6 x 104 L/mol for the association constant of albumin for T, the calculated albumin-bound T varied from 7.14 nmol/L (40 g/L albumin) to 7.80 nmol/L (50 g/L albumin). In view of the relatively unimportant changes in FT, when the albumin concentration varies by as much as 25%, it was concluded that for routine purposes FT could be calculated assuming an albumin concentration of 43 g/L (6.2 x 10-4 mol/L) if one is not dealing with sera from patients with marked abnormalities in plasma protein composition, such as in nephrotic syndrome or cirrhosis of the liver, or with sera obtained during pregnancy, in which cases the actual albumin concentration should be taken into account1.

A symptomatic response to T therapy is generally seen within 3 months. Monitoring should occur at least 2-3 times during the first year, and 1-2 times per year thereafter. Monitoring should include serum T, PSA levels, and hematocrit/ hemoglobin. There is no need to measure liver or renal function tests for any of the routine T-therapy formulations2.

References

  • Trost LW, Mulhall JP. Challenges in Testosterone Measurement, Data Interpretation, and Methodological Appraisal of Interventional Trials. The journal of sexual medicine. Jul 2016;13(7):1029−46. Return to content
  • Antonio L, Wu FC, O'Neill TW, et al. Low Free Testosterone Is Associated with Hypogonadal Signs and Symptoms in Men with Normal Total Testosterone. J Clin Endocrinol Metab. Jul 2016;101(7):2647- 57. Return to content
  • Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. Oct 1999;84(10):3666-72. Return to content