Testosterone blood test: total, free and what low levels mean

Total, free and bioavailable testosterone

• Total testosterone measures both the testosterone bound to proteins and the free form. It is the most common test and the one guidelines use for diagnosis.
• Free testosterone measures only the unattached form, which the body can use most easily. It helps when total testosterone is borderline or doesn't match symptoms. See the free testosterone lab guide.
• Bioavailable testosterone adds free testosterone and the part loosely bound to proteins other than SHBG. It is rarely ordered. SHBG itself is often checked to help interpret results.

Timing and preparation

Testosterone peaks in the morning and changes through the day, so draw it between about 7 and 10 a.m. A single low result is often repeated, because levels vary from day to day.

1. Book a morning draw. Your lab may ask you to fast for several hours.
2. Tell your clinician about every medicine and supplement, including any testosterone or other hormones. Don't stop a medicine on your own.
3. Use the same lab for repeat tests when you can, since methods differ.

Low and high testosterone in men

Symptoms of low testosterone can include low sex drive, erectile problems, infertility, loss of muscle, less body hair, enlarged breasts, thinning bones and anemia. Common contributors include obesity, sleep apnea, chronic illness, an underactive thyroid, overtraining, pituitary problems and testicular problems. Testosterone also falls with age, so a low-normal number doesn't always need treatment.

After a confirmed low result, guidelines recommend checking LH, a pituitary hormone, to look for the cause. High testosterone in men is uncommon and can come from anabolic steroids, testosterone use, or rarely a tumor or adrenal condition.

Testosterone in women

Women make much less testosterone. MedlinePlus lists about 8.4 to 48.1 ng/dL for women 17 to 50 and about 2.9 to 40.1 ng/dL after 50; ranges vary by lab and fall with age.

High testosterone in women can cause excess facial or body hair, acne, irregular or absent periods and male-pattern hair loss. Causes include polycystic ovary syndrome (PCOS), congenital adrenal hyperplasia, and ovarian or pituitary conditions. Low levels are usually normal, and extremely low levels can point to adrenal, pituitary or ovarian problems. A comprehensive hormone panel reads testosterone alongside other hormones.

What to do with your result

1. Confirm a low result with a second early-morning test before drawing conclusions.
2. Ask about the cause, including LH, prolactin when it fits, thyroid, sleep apnea and weight.
3. If you are considering testosterone therapy, read what TRT is and its side effects. Therapy needs a clinician's diagnosis and ongoing monitoring, including hematocrit.

A testosterone test alone can't diagnose a condition. See a clinician promptly for new breast lumps, a testicular lump or swelling, or, in women, rapid new hair growth, voice deepening or missed periods.