Sex hormone-binding globulin (SHBG) is a glycoprotein responsible for blood transport of testosterone and estradiol. SHBG is synthesized in the liver and has a high binding affinity for 17-hydroxysteroid hormones.1,2 Less than 2% of biologically active steroids are free in the circulation with the remainder being bound mostly to SHBG and albumin. SHBG has a high binding affinity to the 17-hydroxysteroid hormones while albumin has a low binding affinity.3 Initially, the free portion or unbound hormone fraction was believed to be the only biologically active form. It is now recognized that the portion of hormone that is weakly bound to albumin is also available to the tissues. The free hormone plus the albumin bound portion of hormones represents the “bioavailable” hormone.

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Serum Separator Tube (SST®)

Do not remove the stopper at any time. Do not centrifuge immediately after drawing blood. Allow the blood to clot in an upright position for at least 30 minutes but not longer than 1 hour before centrifugation. Centrifuge for at least 15 minutes at 2200-2500 RPM within one hour of collection. Label the tube with the patient’s last name, patient’s first name, date of birth, date of collection, and time of collection.

Room temperature: 8 Hours
Refrigerated: 7 Days
Frozen: 2 Months