"Testosterone, Free & Total-Adults" Assay Now Available in Clinical Chemistry Laboratory

Effective Wednesday May 4, 2011, the University of Iowa Hospitals and Clinics (UIHC) core clinical chemistry laboratory will start performing the test “TESTOSTERONE-FREE & TOTAL-ADULTS” (Epic # LAB4140).  This will replace the mailout test “TESTOSTERONE-FREE & TOTAL-ADULT MALES”.  The sample requirements are 3 mL whole blood in light green top (plasma separator tube) or TWO microtainers. Testing will be performed 24 hours a day, seven days a week.

This test measures the concentrations of sex-hormone binding globulin and total testosterone in plasma by Roche Diagnostics assays.  The free testosterone concentration is then derived by a mathematical expression based on the binding of testosterone to sex-hormone binding globulin.

This test is not recommended for children (especially girls) less than 18 years old due to the lower levels of testosterone present that may be below the lower limit of the testosterone immunoassay.  For free testosterone measurement in children, the mailout test “TESTOSTERONE, FREE & TOTAL, FEMALE/CHILD” (LAB4141) is available.

The testing should also be used with caution in pregnant women due to changes in sex hormone binding globulin concentrations that occur throughout pregnancy, leading to challenges in interpreting the estimated free testosterone concentrations.

Reference ranges are:

Total testosterone:    
  Adult Males: 19-49 years old 249-836 ng/dL
  50 years and older 193-740 ng/dL
  Adult Females: 19-49 years old 8-48 ng/dL
  50 years and older 2-41 ng/dL
Sex hormone binding globulin:    
  Males:   10-80 nmol/L
  Females, non-pregnant:   20-130 nmol/L
Free testosterone   32-168 pg/mL
% free testosterone   1.1-2.5%

Questions should be directed to Matthew Krasowski, MD, PhD, Medical Director of the Clinical Chemistry Laboratory (384-9380, matthew-krasowski@uiowa.edu).