How to Prepare for an SHBG Blood Test: Rules for Accurate Results

Sex hormone-binding globulin, or SHBG, rarely gets attention on its own, yet it is essential for interpreting testosterone and estrogen results. A poorly timed or poorly prepared blood draw can distort both SHBG and the hormones measured alongside it. Here is how to prepare so your results reflect reality.

What SHBG is and why it matters

SHBG is a protein made mainly in the liver. It binds testosterone, dihydrotestosterone and estradiol in the bloodstream, controlling how much of these hormones is "free" and available to tissues (Hammond, 2011).

Total testosterone includes hormone bound to SHBG, hormone loosely bound to albumin and a small free fraction. Two people with the same total testosterone can have very different free levels if their SHBG differs.

For this reason, the Endocrine Society guideline on testosterone therapy (Bhasin et al., 2018) recommends measuring or calculating free testosterone when total testosterone is near the lower limit or when SHBG may be abnormal, such as in obesity, aging, diabetes, liver disease or thyroid disorders.

Free testosterone is often calculated from total testosterone, SHBG and albumin using equations such as Vermeulen's (Vermeulen et al., 1999), so an accurate SHBG result matters directly.

Factors that change SHBG

Low SHBG is associated with insulin resistance and a higher risk of type 2 diabetes in both men and women (Ding et al., 2009). Simó et al. (2015) described how liver fat and inflammation suppress SHBG production.

In women, SHBG is often measured as part of a workup for polycystic ovary syndrome (PCOS), in which it tends to be low.

Anabolic steroid use typically lowers SHBG markedly, which can distort interpretation of hormone panels.

Preparation rules

SHBG itself does not change dramatically over the day, but it is almost always measured with testosterone, which does. Preparation should therefore follow testosterone rules.

• Have blood drawn in the morning, ideally between 7 and 10 a.m., when testosterone peaks (Brambilla et al., 2009);
• Fasting is commonly recommended, since glucose intake can temporarily lower testosterone;
• Avoid strenuous exercise for 24 to 48 hours before the test;
• Get a normal night's sleep; sleep deprivation lowers testosterone;
• Avoid alcohol for at least 24 hours;
• Stop high-dose biotin supplements for at least 48 to 72 hours, as biotin can interfere with immunoassays, a risk highlighted by the FDA in 2017;
• Do not stop prescription medications without consulting your doctor.

For women, timing in the menstrual cycle matters for sex hormones. Testing is often performed in the early follicular phase (days 2–5) unless your clinician specifies otherwise.

Interpreting results

Reference ranges vary by laboratory, sex and age. Always compare your results with the range on your report.

A single result should be confirmed with a repeat test, especially if it will influence treatment decisions. The Endocrine Society recommends at least two morning measurements of total testosterone to diagnose hypogonadism.

Abnormal SHBG often points to an underlying condition rather than being a problem itself. High SHBG may prompt thyroid and liver tests; low SHBG may prompt glucose and insulin evaluation.

Athletes should disclose any supplements or hormonal substances, as these strongly influence results and interpretation.

Common mistakes

Testing in the afternoon after a hard training session, which may lower testosterone.

Taking hair-skin-nail supplements containing high-dose biotin the morning of the test.

Comparing results from different laboratories with different methods.

Self-interpreting a calculated free testosterone without considering SHBG and albumin.

Conclusions from the editorial team

SHBG is key to understanding how much testosterone and estradiol are actually available to tissues.

Prepare as you would for a testosterone test: morning draw, fasting, rest from hard exercise, good sleep, no alcohol and no biotin.

Abnormal SHBG often signals other conditions, such as thyroid, liver or metabolic disorders, and deserves medical follow-up.

Related topics on our site: hematocrit for athletes, testicular atrophy and lab tests on rosuvastatin.

References

1. Hammond GL. Diverse roles for sex hormone-binding globulin in reproduction. Biol Reprod. 2011;85(3):431–441.
2. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744.
3. Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666–3672.
4. Brambilla DJ, Matsumoto AM, Araujo AB, McKinlay JB. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men. J Clin Endocrinol Metab. 2009;94(3):907–913.
5. Ding EL, Song Y, Manson JE, et al. Sex hormone-binding globulin and risk of type 2 diabetes in women and men. N Engl J Med. 2009;361(12):1152–1163.
6. Simó R, Sáez-López C, Barbosa-Desongles A, Hernández C, Selva DM. Novel insights in SHBG regulation and clinical implications. Trends Endocrinol Metab. 2015;26(7):376–383.
7. U.S. Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. Silver Spring (MD): FDA; 2017.