Testosterone, Free and Total with SHBG
The Testosterone, Free and Total with SHBG panel measures total testosterone, sex hormone-binding globulin, and derived free and bioavailable testosterone — providing the complete androgen bioavailability assessment that total testosterone alone cannot deliver.
4
Biomarkers
Blood (serum)
Sample
1–3 business days
Turnaround
No — fasting is not required for the testosterone panel. However, morning collection (07:00–10:00) is recommended for male hypogonadism diagnostic evaluation to capture the diurnal testosterone peak; the Endocrine Society recommends confirmation of low testosterone on two morning specimens before initiating testosterone replacement therapy. For monitoring of established TRT or for female assessments, collection time is less critical but should be documented for consistency in serial monitoring.
Fasting
What is the Free & Total Testosterone w/ SHBG test?
The Testosterone, Free and Total with SHBG panel provides the complete androgen bioavailability assessment by simultaneously measuring total testosterone, calculating free and bioavailable testosterone, and quantifying SHBG — the binding protein whose concentration is the dominant determinant of how much of the total testosterone pool is biologically accessible to tissues. No single testosterone parameter in isolation provides a complete androgen status assessment; the combination of total testosterone, SHBG, and derived free and bioavailable testosterone offers a dimensionally complete picture that accounts for individual variation in binding protein concentration. This panel is clinically indicated in any scenario where androgen bioavailability — rather than total testosterone mass alone — is the clinical question. This includes virtually all evaluations of hypogonadism in males where ageing, obesity, liver disease, or thyroid dysfunction alter SHBG; all evaluations of androgen excess in females where PCOS-associated SHBG suppression amplifies the clinical impact of modestly elevated testosterone; testosterone replacement therapy initiation, dose titration, and monitoring in both sexes; PCOS androgen excess characterisation; and sexual dysfunction, libido, musculoskeletal, cognitive, and metabolic complaints in any patient where androgen status is a plausible contributing factor. The panel is also the appropriate first test in males with suspected hypogonadism — providing simultaneously the total testosterone, free testosterone, and SHBG needed to apply the Endocrine Society's diagnostic threshold framework before progressing to LH, FSH, and prolactin for aetiological characterisation.
What does the Free & Total Testosterone w/ SHBG test measure?
Testosterone is the primary androgenic steroid hormone in humans, synthesised predominantly by testicular Leydig cells in males — constituting approximately 95% of circulating testosterone — under LH stimulation from the anterior pituitary, and by ovarian theca cells and adrenal zona reticularis in females. Total testosterone represents the combined pool of all circulating testosterone: protein-bound testosterone (approximately 44–65% bound to sex hormone-binding globulin [SHBG] with high affinity — not bioavailable; approximately 30–44% loosely bound to albumin — considered bioavailable) and the small free fraction (approximately 2–3% in males, 1–2% in females — biologically active). Testosterone exerts its effects by binding the androgen receptor (AR) directly and through intracellular 5-alpha reductase conversion to the more potent dihydrotestosterone (DHT), and through peripheral aromatase (CYP19A1) conversion to estradiol. In males, testosterone plasma half-life is approximately 10–100 minutes; the testicular production rate is approximately 5–7 mg/day. The hypothalamic-pituitary-gonadal (HPG) axis regulates testosterone through negative feedback — rising testosterone and estradiol (from aromatisation) suppress GnRH and LH, limiting further testicular stimulation.
Total testosterone is the first-line androgen assessment marker in both males and females. In males, it provides the primary diagnostic measurement for hypogonadism — the most common androgen deficiency state, with prevalence increasing substantially with age, obesity, and systemic illness. Total testosterone interpretation requires concurrent assessment of LH and FSH to distinguish primary (testicular failure — high LH, high FSH, low testosterone) from secondary (hypothalamic-pituitary failure — low LH, low FSH, low testosterone) hypogonadism, which has different aetiological and therapeutic implications. However, total testosterone alone provides an incomplete picture of androgen bioavailability because SHBG binds testosterone with high affinity and sequester it from tissue uptake — elevated SHBG (from ageing, liver disease, thyroid hormones, or oestrogen) reduces bioavailable testosterone despite normal total testosterone, and reduced SHBG (from insulin resistance, obesity, androgens, or glucocorticoids) increases bioavailable testosterone despite modestly reduced total testosterone. This is why the panel includes free testosterone and SHBG as essential interpretive companions.
Sex hormone-binding globulin is a homodimeric 90 kDa beta-globulin glycoprotein synthesised primarily by hepatocytes, with each dimer capable of binding one molecule of steroid hormone with high affinity — testosterone, DHT (the highest affinity), and estradiol binding at the same steroid-binding domain with decreasing affinity respectively. SHBG binds approximately 44–65% of circulating testosterone in males (with somewhat variable values cited across studies) and a higher proportion in females, where total testosterone concentrations are lower and SHBG concentrations often higher due to oestrogen exposure. Hepatic SHBG synthesis is strongly upregulated by oestrogens, thyroid hormones (T3), and growth hormone, and strongly downregulated by androgens, insulin, insulin-like growth factor-1 (IGF-1), and glucocorticoids. This regulatory profile makes SHBG a sensitive metabolic barometer — it falls with insulin resistance and rises with oestrogen exposure or thyroid axis activation — providing clinically important interpretive context for total testosterone and free testosterone calculations.
SHBG is the critical interpretive companion to total testosterone — without SHBG, total testosterone cannot be accurately contextualised as representing actual androgen bioavailability. Elevated SHBG (from ageing, liver disease, hyperthyroidism, OCP, HRT, or caloric restriction) reduces the free and bioavailable testosterone fractions despite normal or even high-normal total testosterone, producing symptomatic androgen deficiency that total testosterone alone would not identify. Conversely, reduced SHBG (from insulin resistance, obesity, exogenous androgens, progestogens, or glucocorticoids) increases free and bioavailable testosterone fractions despite low-normal total testosterone, potentially explaining androgenic signs in women with apparently normal total testosterone. In males, low SHBG alongside normal total testosterone but low free testosterone is a clinically meaningful pattern — particularly in obese, insulin-resistant patients — where the low SHBG reduces the total testosterone threshold at which symptoms of androgen deficiency occur. In females, SHBG is the denominator of the Free Androgen Index (FAI) and is central to diagnosing the metabolic androgen excess of PCOS.
Free testosterone represents the unbound, biologically active fraction of total testosterone — approximately 2–3% of total testosterone in males and approximately 1–2% in females — that freely diffuses across cell membranes to bind intracellular androgen receptors and initiate genomic and non-genomic androgenic actions. Free testosterone is in dynamic equilibrium with SHBG-bound and albumin-bound fractions — as free testosterone is metabolised or extracted by target tissues, it is replenished from the albumin-bound pool, which is in rapid equilibrium with the free pool. The gold-standard measurement method is equilibrium dialysis — separating free hormone from bound by dialysis across a semipermeable membrane — which is technically demanding and not available on high-throughput clinical analysers. The calculated free testosterone using the Vermeulen equation — (Total T, SHBG, and albumin as inputs) — provides a validated clinical approximation that correlates well with equilibrium dialysis in most clinical contexts and is the method used by most commercial laboratories including LabCorp for this panel.
Free testosterone is the biologically actionable fraction and the most clinically meaningful testosterone parameter when SHBG alterations are present or suspected — the scenarios where total testosterone misrepresents the actual androgen exposure experienced by tissues. A male with total testosterone of 380 ng/dL and SHBG of 65 nmol/L has a free testosterone below the lower reference limit and will have symptomatic hypogonadism despite a technically 'low-normal' total testosterone. Conversely, a male with total testosterone of 380 ng/dL and SHBG of 15 nmol/L (from obesity and insulin resistance) has a free testosterone at the mid-reference range and no functional androgen deficiency. This is why the Endocrine Society's 2018 testosterone guideline recommends measuring free testosterone using a reliable method in all patients with conditions that alter SHBG — ageing, obesity, diabetes, liver disease, thyroid disease, HIV, OCP/HRT use. Free testosterone is the clinical standard for testosterone deficiency assessment in women because total testosterone assays are relatively insensitive at the low female concentration range; the free and bioavailable fractions provide the functionally relevant androgen index.
Bioavailable testosterone encompasses both the freely circulating unbound fraction and the albumin-loosely-bound fraction — the two fractions collectively available for uptake by target tissues. Albumin-bound testosterone, though protein-bound, dissociates rapidly from albumin's low-affinity single binding site as blood transits through tissues, making it effectively available for cellular uptake during capillary transit — the 'free hormone hypothesis' extended to weakly-bound fractions. SHBG-bound testosterone, by contrast, dissociates very slowly and is considered non-bioavailable at standard physiological conditions. Bioavailable testosterone therefore captures a larger and arguably more complete measure of androgen availability than free testosterone alone, particularly in conditions where total testosterone is normal but SHBG is substantially altered.
Bioavailable testosterone is the most comprehensive measure of androgen bioavailability in the context of SHBG alterations. In males with elevated SHBG — from ageing, liver disease, or hyperthyroidism — bioavailable testosterone may be reduced even when free testosterone appears adequate, providing an additional layer of androgen status characterisation. In females, bioavailable testosterone and the Free Androgen Index (FAI = [Total T × 100] ÷ SHBG) are more widely used than absolute free testosterone because of the sensitivity limitations of direct assays at very low female testosterone concentrations. In the PCOS context, a high FAI from low SHBG (driven by hyperinsulinaemia) in the presence of mildly elevated total testosterone captures the full androgen excess burden that neither total testosterone nor SHBG alone would reveal.
Why is the Free & Total Testosterone w/ SHBG test ordered?
- Male hypogonadism diagnosis and staging — simultaneous total testosterone, free testosterone, and SHBG for the complete androgen status assessment needed to apply Endocrine Society diagnostic criteria; free testosterone is required when total testosterone is borderline and SHBG alterations (ageing, obesity, liver disease) are likely to affect bioavailability
- Testosterone replacement therapy (TRT) initiation and monitoring — pre-treatment baseline panel establishing total testosterone, SHBG, and free testosterone before TRT commencement; serial monitoring at 3–6 month intervals during dose titration to confirm therapeutic range achievement and exclude supra-physiological elevation
- PCOS androgen excess characterisation in females — total testosterone alongside SHBG for Free Androgen Index (FAI) calculation; SHBG is typically suppressed by insulin resistance in the metabolic PCOS phenotype, amplifying the clinical impact of modestly elevated total testosterone; FAI provides the complete androgen bioavailability index in this context
- Female androgen deficiency assessment — libido loss, reduced energy, decreased musculoskeletal vitality, and sexual dysfunction in peri- and postmenopausal women where androgen deficiency is a plausible contributor; free testosterone provides the bioavailable androgen measurement that total testosterone assays underestimate in the low-concentration female range
- Unexplained male infertility and sexual dysfunction — testosterone with SHBG to assess androgen status as part of the male infertility evaluation; concurrent LH and FSH characterise the HPG axis aetiology when testosterone is abnormal
- Metabolic syndrome and insulin resistance androgen assessment — SHBG as an independent insulin resistance barometer (low SHBG correlates with elevated fasting insulin, elevated triglycerides, and central adiposity); the SHBG:testosterone relationship characterises the sex hormone profile of the metabolic syndrome phenotype in both males and females
- Monitoring anabolic-androgenic steroid (AAS) use and misuse — total testosterone and SHBG in the context of suspected AAS misuse (where exogenous testosterone suppresses LH, FSH, and endogenous testicular testosterone while elevating total testosterone); SHBG provides the binding protein context and LH/FSH add the HPG axis suppression evidence
- Integrative medicine comprehensive sex hormone and metabolic baseline — testosterone with SHBG as the androgen component of a comprehensive sex hormone panel alongside estradiol, progesterone, LH, FSH, DHEA-S, and cortisol for personalised hormone optimisation assessment in either sex
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No — fasting is not required for the testosterone panel. However, morning collection (07:00–10:00) is recommended for male hypogonadism diagnostic evaluation to capture the diurnal testosterone peak; the Endocrine Society recommends confirmation of low testosterone on two morning specimens before initiating testosterone replacement therapy. For monitoring of established TRT or for female assessments, collection time is less critical but should be documented for consistency in serial monitoring.
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Standard venipuncture into a serum separator tube (SST / gold top). Document on the requisition form: (1) exact collection time — particularly relevant for male hypogonadism assessment; (2) current testosterone therapy — formulation (injectable, gel, patch, pellet, buccal lozenge), dose, most recent application or injection date and time; trough vs peak timing context; (3) oral contraceptives or exogenous oestrogen — directly elevates SHBG and reduces free testosterone; (4) anabolic steroid use — suppresses LH/FSH and alters total testosterone; (5) current corticosteroid use — reduces SHBG; (6) known insulin resistance, obesity, or metabolic syndrome — reduces SHBG; (7) thyroid disease status and treatment — bidirectional SHBG effects; (8) female menstrual cycle day and menopausal status — relevant for female testosterone and SHBG interpretation; (9) whether concurrent LH, FSH, prolactin, or oestradiol are being ordered simultaneously. # REVIEWER FLAG: Confirm LabCorp SST tube type, minimum serum volume, centrifugation and separation requirements, and specimen stability for both testosterone and SHBG before publication.
Specimen requirements
Minimum 1.0 mL serum for the three-analyte panel (total testosterone, SHBG, and calculated free/bioavailable testosterone). Centrifuge and separate serum within 2 hours of collection. Stable at 2–8°C for up to 7 days; stable frozen at −20°C for extended storage. # REVIEWER FLAG: Confirm minimum volume and stability data — confirm whether a single SST tube provides sufficient volume for all analytes in this panel with LabCorp.
What can affect Free & Total Testosterone w/ SHBG results?
Because free and bioavailable testosterone are derived from total testosterone and SHBG, any condition altering SHBG substantially changes free testosterone independently of testicular or ovarian testosterone production. SHBG is elevated by: oestrogen exposure (OCP, HRT, liver disease, pregnancy) — raising SHBG and reducing free T despite normal total T; ageing — progressive SHBG elevation reduces free and bioavailable testosterone more than total testosterone with each decade; hyperthyroidism — thyroid hormones stimulate hepatic SHBG production; caloric restriction and anorexia. SHBG is reduced by: insulin resistance and obesity — hyperinsulinaemia suppresses hepatic SHBG synthesis; exogenous androgens and anabolic steroids; glucocorticoids; hypothyroidism; nephrotic syndrome. The SHBG context — reported on the same panel — is essential for all testosterone interpretations.
Total testosterone exhibits modest but clinically meaningful diurnal variation in males — peaking in the early morning (approximately 07:00–10:00) and declining by approximately 20–35% through the afternoon. This variation is most pronounced in younger males and attenuates with ageing. For diagnosis of hypogonadism, the Endocrine Society recommends morning collection (07:00–10:00) when testosterone is at its daily peak — an afternoon low-normal result may reflect diurnal decline rather than true hypogonadism. In females, diurnal testosterone variation exists but is smaller and less clinically significant than in males. Collection time must be documented; for hypogonadism diagnostic purposes, morning collection is standard.
Patients receiving any form of exogenous testosterone (intramuscular injections, subcutaneous pellets, transdermal gels or patches, buccal lozenges) have serum testosterone levels that fluctuate substantially in relation to the delivery profile of their formulation. For intramuscular cypionate or enanthate injections (administered every 7–14 days), collection for trough-level monitoring should occur immediately before the next scheduled injection; mid-cycle collection reflects the peak rather than the trough. For daily transdermal gel, collection timing relative to the most recent application must be standardised. Dose timing and formulation must be precisely documented on the requisition form for monitoring results to be interpretable.
Obesity reduces total and free testosterone in males through multiple converging mechanisms: increased peripheral aromatase activity in adipose tissue converts testosterone to oestradiol, which suppresses LH and GnRH through negative feedback; hyperinsulinaemia suppresses SHBG synthesis, which paradoxically increases free testosterone relative to total testosterone while reducing total testosterone; adipokines suppress testicular Leydig cell function; and elevated oestradiol from peripheral aromatisation provides additional HPG axis suppression. In obese males, total testosterone is often substantially below the reference range without true primary hypogonadism — weight loss alone can substantially restore testosterone levels. BMI must be documented when interpreting testosterone in this context.
Standard immunoassay platforms — while adequate at mid-to-high male testosterone concentrations — systematically overestimate testosterone at the low concentrations relevant to females, children, and hypogonadal males, due to non-specific antibody cross-reactivity with testosterone metabolites and other steroids. LC-MS/MS provides isomer-specific measurement with accuracy across the full clinical concentration range. The Endocrine Society and ESHRE recommend LC-MS/MS for testosterone measurement, particularly in females and in hypogonadism diagnosis where values near the lower reference limit require precision. # REVIEWER FLAG: Confirm which LabCorp test code under this panel uses LC-MS/MS vs immunoassay — the methodology materially affects accuracy at low concentrations and should be documented for practitioners ordering in female and elderly populations.
Thyroid hormones — particularly T3 — are potent stimulators of hepatic SHBG synthesis. Hypothyroidism reduces SHBG, lowering total testosterone while increasing free testosterone bioavailability; it may also reduce testicular testosterone production directly through impaired HPG axis function. Hyperthyroidism substantially elevates SHBG, reducing free testosterone and bioavailable testosterone despite normal or elevated total testosterone, and can produce symptoms of androgen deficiency in hyperthyroid males through this mechanism. TSH should be assessed when SHBG is unexpectedly elevated or reduced without an obvious alternative explanation.
What do Free & Total Testosterone w/ SHBG results mean?
Elevated
Elevated total testosterone in males (above 916 ng/dL or the LabCorp upper reference limit in the absence of exogenous testosterone) warrants investigation for exogenous testosterone or anabolic steroid use (the most common cause), late-onset testosterone rebound from prior suppression, or — rarely — testicular or adrenal androgen-secreting tumour. Elevated total testosterone in females (above 55 ng/dL) alongside elevated or low-normal SHBG requires PCOS evaluation (LH:FSH ratio, insulin, ultrasound), non-classical CAH (17-OHP), or adrenal androgen-secreting tumour (add DHEA-S, androstenedione) to the investigation. Elevated free testosterone in a female with normal total testosterone but low SHBG confirms androgen excess from SHBG suppression — typically insulin-driven in the PCOS metabolic phenotype.
Normal
Total testosterone within the reference range does not exclude clinically significant androgen deficiency when SHBG is substantially elevated — calculate free and bioavailable testosterone, and assess symptom burden, LH, and FSH in the clinical context. A normal total testosterone with low SHBG and elevated free testosterone in a symptomatic male effectively confirms adequate androgen bioavailability despite a low-normal total testosterone. In females, a normal total testosterone with suppressed SHBG and elevated FAI confirms androgen excess from SHBG suppression even when total testosterone does not exceed the female reference range — this pattern is characteristic of insulin-resistant PCOS.
Reduced
Low total testosterone in males — confirmed on a morning specimen on two occasions — defines hypogonadism requiring concurrent LH and FSH to localise the defect: low LH and FSH with low testosterone = secondary/central hypogonadism (hypothalamic or pituitary pathology — check prolactin, MRI pituitary); high LH and FSH with low testosterone = primary hypogonadism (testicular failure — check karyotype for Klinefelter syndrome, assess testicular history). Low free testosterone with normal or borderline total testosterone and elevated SHBG is the ageing male pattern — SHBG rises with age while testicular production declines, compressing the free testosterone more than the total. In females, low free testosterone with reduced libido, fatigue, and musculoskeletal decline — particularly post-oophorectomy, post-menopausal, or on OCP — supports androgen deficiency contributing to symptoms, though no universally accepted female testosterone deficiency threshold exists in mainstream guidelines.
Note: The three most clinically important caveats for this panel are: (1) methodology — direct analogue immunoassay free testosterone is inaccurate and not endorsed by the Endocrine Society; practitioners must confirm whether LabCorp calculates free testosterone or measures it by direct assay, and whether total testosterone is measured by LC-MS/MS (preferred) or immunoassay; (2) collection timing — morning collection (07:00–10:00) is required for hypogonadism diagnosis in males; afternoon results may miss a low-morning testosterone that would meet diagnostic criteria; and (3) SHBG confounders — a normal total testosterone in a patient with markedly elevated SHBG (from ageing, liver disease, or OCP) may represent significant free testosterone deficiency; SHBG and free testosterone together, not total testosterone alone, define the functional androgen status.
Frequently asked questions
SHBG is the high-affinity binding protein that sequesters the majority of circulating testosterone in a non-bioavailable form. A patient with high SHBG has less free and bioavailable testosterone per unit of total testosterone, potentially experiencing androgen deficiency symptoms despite a technically normal total testosterone value. Without SHBG, total testosterone cannot be accurately contextualised as representing actual androgen bioavailability at the tissue level — SHBG is the essential interpretive denominator for the entire panel.
How to access the Free & Total Testosterone w/ SHBG test
The Free & Total Testosterone w/ SHBG reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: May 24, 2026
Last reviewed: May 24, 2026
- Bhasin S, et al. Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. (2018)
- Vermeulen A, et al. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. (1999)
- Rosner W, et al. Position statement: Utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society position statement. J Clin Endocrinol Metab. (2007)
- Teede HJ, et al. Recommendations from the international evidence-based guideline for the assessment and management of polycystic ovary syndrome. Hum Reprod. (2018)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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