SHBG: Which Tests to Order Alongside for a Complete Hormone Picture

What SHBG Actually Does and Why It Matters

Sex hormone-binding globulin is a glycoprotein synthesized primarily in hepatocytes. It binds circulating testosterone with high affinity and estradiol with somewhat lower affinity, controlling the fraction of each hormone that remains "free" and able to enter target cells. Only about 1-3% of total testosterone circulates unbound in men [1].

That small free fraction does the biological work. A man with a total testosterone of 500 ng/dL and an SHBG of 60 nmol/L may have a lower calculated free testosterone than a man at 400 ng/dL with an SHBG of 20 nmol/L. The 2018 Endocrine Society guideline for male hypogonadism explicitly recommends measuring SHBG when total testosterone falls in the borderline range (264-400 ng/dL), because SHBG context determines whether that borderline number represents genuine androgen deficiency or adequate free hormone [2]. Without SHBG, a borderline total T is ambiguous. With it, the picture clarifies.

SHBG also responds to metabolic, hepatic, and thyroid signals, which makes it a secondary window into those systems. Ordering it in isolation, though, wastes that window. The paired tests described below turn SHBG from a single data point into a diagnostic lens.

The Core Pair: Total Testosterone and Free Testosterone

Total testosterone is the first test to order with SHBG because the two numbers are interdependent. The Endocrine Society's 2018 clinical practice guideline recommends confirming hypogonadism with a morning total testosterone measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and then calculating free testosterone when SHBG abnormalities are suspected [2].

Free testosterone can be measured directly by equilibrium dialysis, but this assay is expensive and not widely available. Most clinicians instead calculate free T using the Vermeulen equation, which requires three inputs: total testosterone, SHBG, and albumin [3]. The calculation correlates well with equilibrium dialysis results (r = 0.9606 in the original Vermeulen validation) and is endorsed by the Endocrine Society as an acceptable alternative [2].

Albumin therefore belongs on the lab order. It is inexpensive, and without it the Vermeulen calculation cannot run. A standard comprehensive metabolic panel (CMP) includes albumin, so if you are already ordering a CMP, the input is covered.

Practical ordering rule: if you order SHBG, always order total testosterone and albumin in the same draw. This three-test set produces a calculated free testosterone without an extra visit or a specialty assay.

Estradiol: The Other Hormone SHBG Binds

SHBG binds estradiol at roughly one-third the affinity it has for testosterone [4]. In men on testosterone replacement therapy (TRT), rising estradiol can increase SHBG, which then binds more testosterone, potentially blunting the clinical response. In premenopausal women, SHBG fluctuations across the menstrual cycle alter free estradiol availability and can influence symptom patterns.

The 2020 AACE/ACE guideline on male hypogonadism recommends monitoring estradiol in men receiving TRT, particularly when gynecomastia or mood changes develop [5]. Ordering estradiol with SHBG at baseline gives the clinician both sides of the binding equation and establishes a reference point for future monitoring.

Use the sensitive estradiol assay (LC-MS/MS) in men. Standard immunoassay estradiol tests were designed for female reproductive ranges and lose accuracy below 30 pg/mL, which is exactly where most male values fall [6].

Thyroid Panel: TSH and Free T4

Thyroid hormones directly regulate hepatic SHBG synthesis. Hyperthyroidism increases SHBG, sometimes dramatically. A 1994 study in the Journal of Clinical Endocrinology & Metabolism found that SHBG levels fell by a mean of 52% after successful treatment of hyperthyroidism with radioiodine [7]. Hypothyroidism does the opposite, suppressing SHBG and potentially masking androgen deficiency by making total testosterone appear adequate while free T is low.

A TSH alone will screen for most thyroid dysfunction. If TSH is abnormal, free T4 and free T3 reflex testing completes the picture. The American Thyroid Association recommends TSH as the initial screening test for thyroid disease [8].

Order TSH with every initial SHBG panel. If a patient presents with unexplained high SHBG and no liver disease, an overactive thyroid is a common culprit. Treating the thyroid problem often normalizes SHBG without any direct hormone intervention.

Fasting Insulin and Glucose: The Metabolic Connection

Insulin is one of the strongest suppressors of SHBG. Hepatocytes reduce SHBG production when exposed to high insulin concentrations, and multiple epidemiologic studies confirm the inverse relationship. The Inter99 cohort study (N=2,470 men and 3,115 women) demonstrated that fasting insulin was the single strongest predictor of low SHBG after adjusting for BMI, age, and sex [9].

A fasting insulin and fasting glucose (or HbA1c) alongside SHBG can reveal subclinical insulin resistance before it progresses to overt diabetes. The American Diabetes Association's 2024 Standards of Care recommend screening for type 2 diabetes in adults with overweight (BMI ≥25 kg/m²) starting at age 35, and earlier in the presence of risk factors [10]. Low SHBG itself may be one of those risk factors. A meta-analysis published in JAMA (N=27,657 women across 10 prospective studies) found that each standard-deviation decrease in SHBG was associated with an 80% increase in the odds of developing type 2 diabetes in women (OR 1.80 to 95% CI 1.47-2.21) [11].

Fasting insulin is not a standard panel test, so you must order it explicitly. Draw it alongside SHBG in a fasting morning sample to minimize diurnal and postprandial variability.

Hepatic Function Panel: ALT, AST, and GGT

The liver makes SHBG. Liver disease can push SHBG in either direction depending on the type and severity, but chronic liver disease and cirrhosis commonly raise SHBG because of increased estrogen-to-androgen ratios and altered hepatic clearance [12]. Non-alcoholic fatty liver disease (now termed metabolic dysfunction-associated steatotic liver disease, or MASLD), by contrast, is associated with low SHBG through its link to insulin resistance [13].

A hepatic function panel (ALT, AST, alkaline phosphatase, total bilirubin) screens for occult liver injury that could explain an unexpected SHBG result. Adding GGT increases sensitivity for alcohol-related or biliary pathology. This panel is inexpensive and widely available.

"SHBG is as much a liver test as it is a hormone test," notes the Endocrine Society's 2018 guideline, which recommends evaluating hepatic function when SHBG is unexpectedly elevated [2].

Prolactin: When to Add It

Prolactin is not a routine companion to SHBG, but it belongs on the panel when a male patient presents with very low testosterone (total T <150 ng/dL), loss of libido, or visual field changes suggesting a pituitary lesion. Hyperprolactinemia suppresses GnRH pulsatility, leading to secondary hypogonadism that will show up as low total T with an inappropriately normal or low LH [2].

The Endocrine Society recommends measuring prolactin in all men with secondary hypogonadism [2]. If SHBG testing is part of a hypogonadism workup and LH/FSH come back low, prolactin should be added to rule out prolactinoma.

Order it from the same morning fasting sample. Prolactin rises with stress, venipuncture, and meals, so a calm, fasted draw gives the most reliable baseline.

LH and FSH: Distinguishing Primary from Secondary Hypogonadism

Luteinizing hormone and follicle-stimulating hormone tell you whether a low testosterone is the testicle's fault (primary, with elevated LH/FSH) or the pituitary's fault (secondary, with low or inappropriately normal LH/FSH). This distinction changes treatment. Primary hypogonadism typically requires exogenous testosterone. Secondary hypogonadism may respond to clomiphene citrate or warrants MRI to exclude a pituitary mass [2].

SHBG helps refine the testosterone interpretation, while LH/FSH explain its cause. The two tests answer different questions. Order them together in any initial male hormone evaluation.

In women, LH and FSH are useful for evaluating menstrual irregularity, polycystic ovary syndrome (PCOS), and menopausal status. The 2023 international evidence-based guideline for PCOS recommends using a combination of clinical hyperandrogenism, oligo/anovulation, and ultrasound criteria for diagnosis, but notes that a low SHBG is common in PCOS and supports clinical suspicion [14].

DHEA-S: Adrenal Androgen Screening

Dehydroepiandrosterone sulfate (DHEA-S) is produced almost exclusively by the adrenal glands and serves as a reservoir for androgen and estrogen synthesis in peripheral tissues. It is not bound by SHBG with high affinity but is relevant when investigating hyperandrogenism in women, especially when SHBG is suppressed and clinical signs (acne, hirsutism, alopecia) are present [14].

An elevated DHEA-S with a normal testosterone suggests adrenal androgen excess. A very high DHEA-S (>700 mcg/dL in women) raises concern for an adrenal tumor and warrants imaging [15]. Ordering DHEA-S alongside SHBG in the hyperandrogenism workup ensures adrenal contributions are not missed.

How to Interpret SHBG in Context: High, Low, and Normal

Normal SHBG ranges vary by sex, age, and assay, but commonly cited adult reference intervals are 10-57 nmol/L for men and 18-144 nmol/L for premenopausal women [2]. Postmenopausal women not on hormone therapy tend to have values in the lower half of the female range.

High SHBG (above the reference range) reduces free testosterone and may cause symptoms of androgen deficiency even when total T looks normal. Common causes include hyperthyroidism, liver disease, aging, oral estrogen use, and anticonvulsants such as phenytoin and carbamazepine [7]. A 2016 study in Clinical Endocrinology reported that men over age 70 had SHBG levels approximately 1.6 times higher than men aged 20-29 [16].

Low SHBG (below the reference range) increases free testosterone and free estradiol. The most common driver is insulin resistance. Obesity, type 2 diabetes, hypothyroidism, exogenous androgens, and nephrotic syndrome also lower SHBG [9]. In women, low SHBG is a hallmark of PCOS and correlates with metabolic syndrome severity [14].

Interpreting SHBG requires the paired tests. A high SHBG with no obvious cause should prompt thyroid and liver workups. A low SHBG in an overweight patient should trigger metabolic screening.

Strategies for Lowering Elevated SHBG

Treating the underlying cause is the first step. If hyperthyroidism is driving SHBG up, treating the thyroid normalizes SHBG. A small crossover trial (N=12 hypogonadal men) published in the Journal of Clinical Endocrinology & Metabolism showed that low-dose stanozolol (2 mg/day) reduced SHBG by approximately 50%, but anabolic steroids carry hepatotoxicity risk and are not first-line therapy [17]. Boron supplementation at 10 mg/day for seven days reduced SHBG by 9% in a small pilot study (N=8 healthy men), though the clinical significance of this modest change is debatable [18].

If a patient is on oral estrogen (common in postmenopausal women), switching to transdermal estradiol bypasses first-pass hepatic metabolism and typically lowers SHBG. The KEEPS trial demonstrated that transdermal estradiol (50 mcg/day) produced significantly less SHBG elevation than oral conjugated equine estrogen (0.45 mg/day) [19].

Weight loss in obese patients with low SHBG would seem paradoxical since low SHBG is the concern. But weight loss improves insulin sensitivity, and a normalization of the insulin-SHBG axis can correct both the metabolic dysfunction and the suppressed SHBG simultaneously.

Strategies for Raising Low SHBG

Reducing insulin resistance is the most effective intervention. Weight loss, caloric restriction, and exercise all raise SHBG. A 12-month lifestyle intervention study in the Diabetes Prevention Program (N=3,234) found that participants in the intensive lifestyle group had a mean SHBG increase of 11.2% compared with 4.7% in the placebo group [20].

Metformin has mixed effects on SHBG. While it improves insulin sensitivity, the DPP data showed a smaller SHBG increase with metformin (6.0%) than with lifestyle intervention alone [20]. In women with PCOS, combined oral contraceptives raise SHBG substantially by stimulating hepatic synthesis, which is part of their mechanism for reducing clinical hyperandrogenism [14].

Dietary factors may play a role. Higher fiber intake and lower glycemic index diets correlate with higher SHBG in observational data, though randomized trial evidence for dietary SHBG modification is limited [21].

The Recommended Panel: Putting It All Together

For a man presenting for initial hormone evaluation, the minimum SHBG companion panel should include: total testosterone (LC-MS/MS, morning draw), albumin, estradiol (sensitive assay), LH, FSH, TSH, fasting insulin, fasting glucose, and a hepatic function panel. Add prolactin if total T is very low or LH/FSH suggest secondary hypogonadism. Add DHEA-S if adrenal pathology is suspected.

For a woman being evaluated for hyperandrogenism or PCOS, the panel should include: total testosterone, free testosterone (calculated or by equilibrium dialysis), DHEA-S, LH, FSH, TSH, fasting insulin, fasting glucose, 17-hydroxyprogesterone (to screen for non-classic congenital adrenal hyperplasia), and a hepatic function panel [14].

All samples should be drawn fasting, in the morning before 10:00 AM, to minimize diurnal variation in testosterone and cortisol. Repeat any abnormal result on a separate day before making a diagnosis, per Endocrine Society recommendations [2]. The minimum confirmed-abnormal count for diagnosing male hypogonadism is two separate morning total testosterone values below the lower limit of normal.