Testosterone (Total) Blood Test

What Does This Test Measure?

Testosterone is the primary male sex hormone (androgen), produced primarily by the testes in men and in smaller amounts by the ovaries and adrenal glands in women. It regulates libido, muscle mass, bone density, red blood cell production, and mood. Total testosterone includes both protein-bound (~98%) and free (~2%) fractions.

Why Your Doctor Ordered This Test

In men, testing is prompted by symptoms suggestive of androgen deficiency, low libido, erectile dysfunction, unexplained fatigue, decreased muscle strength, loss of body hair, osteoporosis or low-trauma fractures, and anemia. Infertility evaluations, delayed puberty in adolescents, and monitoring patients on testosterone replacement or androgen deprivation therapies also warrant measurement. Additionally, testing is part of the workup for unexplained anemia (since testosterone stimulates red blood cell production) and gynecomastia when an androgen-estrogen imbalance is suspected. In men with rapid virilization or testicular masses, total testosterone can help screen for Leydig cell tumors. For prostate cancer patients on androgen deprivation therapy, periodic measurements confirm castrate-level testosterone (typically <50 ng/dL). The doctor aims to confirm hypogonadism and distinguish between primary testicular failure (e.g., Klinefelter syndrome, testicular trauma, mumps orchitis, chemotherapy) and secondary pituitary/hypothalamic insufficiency (e.g., pituitary tumors, hemochromatosis, opioid use, obesity, obstructive sleep apnea). If total testosterone is low, LH and FSH levels indicate whether the problem is in the testes or central axis.

In women, clinicians order total testosterone when assessing androgen excess conditions such as polycystic ovary syndrome (PCOS), idiopathic hirsutism, acne, androgenetic alopecia, or menstrual irregularities. Elevated total testosterone can point to PCOS, congenital adrenal hyperplasia, insulin resistance, or rarely an ovarian or adrenal androgen-secreting tumor. In postmenopausal women, testosterone may be checked alongside estradiol to evaluate sexual dysfunction or as part of hormone replacement monitoring. In transgender men (female-to-male), total testosterone is monitored to ensure levels are within the male physiological range. In all contexts, the result is interpreted together with free testosterone, SHBG, and other androgens (DHEA-S, androstenedione) to fully assess androgen status.

What High Testosterone Means

High testosterone in men: testosterone supplementation (exogenous), anabolic steroid use, testosterone-producing tumors (Leydig cell or adrenal tumors, rare), and congenital adrenal hyperplasia. High testosterone suppresses LH/FSH, reduces sperm production, and can cause polycythemia (high RBCs). In women: PCOS (most common cause), congenital adrenal hyperplasia, ovarian or adrenal androgen-producing tumors.

What Low Testosterone Means

Low testosterone in men (hypogonadism): primary hypogonadism (testicular failure, low testosterone + high LH/FSH; causes: Klinefelter syndrome, mumps orchitis, trauma, chemotherapy), secondary hypogonadism (pituitary/hypothalamic failure, low testosterone + low/normal LH/FSH; causes: pituitary tumor, hemochromatosis, opioid use, obesity, type 2 diabetes, sleep apnea, chronic illness). Symptoms: low libido, erectile dysfunction, fatigue, depression, loss of muscle mass, and osteoporosis.

How to Prepare and What Affects the Result

To obtain an accurate total testosterone measurement, blood should be drawn in the morning (ideally between 7 and 10 a.m.) to capture the natural morning peak. Fasting is generally not mandatory for testosterone alone, but many clinicians request a fasting sample because a concurrent lipid panel and glucose assessment are often needed in metabolic evaluation. Patients should avoid high-dose biotin (≥5 mg) for at least 48 hours before the test; biotin interference in streptavidin-based immunoassays can cause falsely high or low results. Certain medications and supplements can alter testosterone levels: exogenous testosterone or anabolic steroids elevate levels; opioids, systemic glucocorticoids, GnRH agonists, and spironolactone suppress endogenous production. Strenuous resistance exercise within 24 hours may transiently lower testosterone, while acute illness and severe stress can cause a temporary drop.

Sample should be collected in a serum separator tube, allowed to clot for 30 minutes, and centrifuged promptly. Hemolyzed or lipemic specimens may interfere with immunoassays, so careful handling is important. If biotin interference is a concern or the immunoassay result is discordant with the clinical picture, LC-MS/MS (liquid chromatography–tandem mass spectrometry) methods are preferred because they are unaffected by biotin and cross-reactivity with other steroids, providing a more specific total testosterone value.

Common Misinterpretations

One of the most common misinterpretations is evaluating total testosterone without considering sex hormone binding globulin (SHBG) and free testosterone. Approximately 44–66% of circulating testosterone is tightly bound to SHBG; alterations in SHBG (such as decreased SHBG in obesity, insulin resistance, hypothyroidism, or nephrotic syndrome, and increased SHBG in aging, hyperthyroidism, liver disease, or estrogen therapy) can skew total testosterone while the biologically active free fraction remains normal. A man with obesity and low SHBG may present with low total testosterone but normal free testosterone, leading to a misdiagnosis of hypogonadism and unnecessary testosterone therapy. Conversely, older men with high SHBG may have elevated total testosterone yet low free testosterone, masking true androgen deficiency. Ignoring the diurnal rhythm is another frequent error: testosterone peaks in the early morning and declines across the day; a blood draw in the late afternoon or evening can be 20–40% lower than the morning peak, potentially leading to a false diagnosis of hypogonadism if only a single non-morning value is used.

Assay variability is a significant source of misinterpretation. Immunoassays can yield results that are 10–30% lower than the gold standard LC-MS/MS, especially at low testosterone concentrations (common in women and children). In men, some commercial immunoassays may overestimate testosterone due to cross-reactivity with related steroids, while others underestimate. Without knowing the assay platform, a result just above or below a cutoff may be misjudged. Biotin supplementation (>5 mg) can interfere with streptavidin-based immunoassays, causing falsely high or low results depending on the assay format; patients may be unaware of biotin in hair-skin-nails supplements. Functional causes of low testosterone (such as obesity, opioid use, sleep apnea, and acute illness) can be misread as permanent hypogonadism, leading to lifelong testosterone therapy instead of addressing the reversible condition. In women, a total testosterone value within the normal female range does not exclude androgen excess if SHBG is low; calculation of the free androgen index or free testosterone is needed. Conversely, an elevated total testosterone in a woman using combined oral contraceptives (which increase SHBG) may reflect high SHBG-bound testosterone and not true hyperandrogenism.

Frequently Asked Questions

What does total testosterone measure?

Total testosterone measures the sum of free (unbound) testosterone and testosterone bound to proteins, primarily sex hormone binding globulin (SHBG) and albumin. Only about 2% is free and biologically active; the remainder is tightly bound to SHBG (~44–66%) or loosely bound to albumin (~33–54%). Because SHBG levels vary with age, body weight, insulin resistance, and thyroid function, total testosterone can be misleading without knowing free testosterone or SHBG levels.

Why is SHBG important when interpreting total testosterone?

SHBG binds most circulating testosterone and controls its bioavailability. When SHBG is low (common in obesity, diabetes, and hypothyroidism) total testosterone may appear deceptively low even though free testosterone is normal. Conversely, high SHBG (aging, hyperthyroidism, liver disease, estrogen therapy) can inflate total testosterone while reducing free testosterone. Therefore, a total testosterone result without an SHBG measurement risks misdiagnosing hypogonadism or androgen excess.

What time of day should I get a testosterone blood test?

Testosterone follows a diurnal rhythm, peaking in the early morning and declining through the day. For accurate assessment, blood should be drawn between 7 and 10 a.m., after an overnight fast if possible. A late afternoon draw can be 20–40% lower than the morning peak, which could falsely suggest low testosterone. If you must test later, note the collection time and discuss it with your healthcare provider; two separate morning draws are recommended to confirm hypogonadism.

Can biotin supplements affect total testosterone results?

Yes, high-dose biotin (≥5 mg) can interfere with the immunoassays commonly used to measure total testosterone. Many laboratories use streptavidin-biotin binding in their assay design; excess biotin in the blood can compete with the assay’s biotinylated components, causing falsely elevated or falsely low results depending on the specific assay format. To avoid this, stop biotin supplements at least 48 hours before your blood draw. LC-MS/MS methods are not affected by biotin and provide a reliable alternative if biotin use cannot be paused.

What is the difference between total and free testosterone?

Total testosterone includes all testosterone in the bloodstream, free, albumin-bound, and SHBG-bound. Free testosterone (about 2% of total) is unbound and biologically active, capable of entering cells and binding androgen receptors. Albumin-bound testosterone (~33–54%) is weakly bound and can also become bioavailable, while SHBG-bound testosterone (~44–66%) is tightly bound and unavailable to tissues. Because SHBG levels fluctuate, total testosterone may not reflect the amount usable by the body, making free or bioavailable testosterone a critical complementary measurement.

Related Markers: Read Together for Full Context

BloodWorker reads lab values together, not in isolation. These related markers provide essential context for interpreting your Testosterone result: