The Testosterone Free Direct test measures the amount of testosterone that is not bound to proteins in the blood and is freely available for the body to use. Most testosterone in the blood is attached to proteins such as sex hormone-binding globulin (SHBG) and albumin, while only a small portion circulates freely. This test uses a direct measurement method to estimate that free fraction. The test is used to help evaluate testosterone activity in the body, especially when total testosterone results may be affected by changes in binding proteins. It is often ordered to help assess symptoms that may be related to low or high testosterone levels in both men and women. Free testosterone can provide additional information beyond total testosterone.