A Guide to Understanding Hormones Detected in Testosterone Blood Tests 

Take-home points

• Testosterone regulates sex differentiation, muscle development, voice deepening, hair growth, sperm production, and libido.
• As men age, declining testosterone levels can reduce energy, muscle mass, increase body fat, and decrease bone density, affecting quality of life.
• Testing testosterone levels is essential, often done through blood tests, but at-home kits can yield inaccurate results without professional guidance.
• Comprehensive evaluation by healthcare professionals ensures accurate diagnosis and effective treatment, considering factors like free and total testosterone, SHBG, prolactin, LH, and FSH.

Testosterone is the primary male hormone that plays a considerable role in regulating sex differentiation and producing male sex characteristics.¹ It influences puberty, contributing to the development of muscles, deepening the voice, and promoting hair growth. Throughout a man's life, testosterone continues to be essential for sperm production and maintaining libido.¹

As men age, testosterone levels naturally decline. This drop can lead to noticeable changes such as reduced energy, lower muscle mass, increased body fat, and decreased bone density.¹ These changes can affect overall quality of life and may indicate underlying health issues that require medical attention. Recognising the signs of low testosterone is therefore important for timely intervention and management.¹

Learn more about the signs and symptoms of low testosterone

An essential part of management is getting your testosterone levels checked. This is often done through a blood test with your clinician, or, depending on your preferences, an at-home test using a finger prick method. However, understanding your testosterone levels is difficult and warrants the need for physician intervention.  

Learn more about the accuracy of at-home testing vs. a clinical test with your clinician

Testosterone tests are usually conducted between 8 AM and 10 AM, when testosterone levels are at their peak.¹ The results of these tests can provide valuable insights into your health. Low testosterone levels may signal conditions such as hypogonadism, where the body doesn't produce enough testosterone.¹ Conversely, abnormally high levels can also indicate health issues, including hormone imbalances.

Preparing for your testosterone test: Find out more

The important part

In recent years, at-home testosterone test kits have gained popularity, providing a convenient way to monitor hormone levels. However, these kits can sometimes yield skewed results due to variations in testing conditions and methodologies.² Factors such as the time of day, fasting state, and individual lab standards can significantly impact the accuracy of these tests. Without the guidance of a healthcare professional, interpreting these results can be challenging and may lead to incorrect conclusions about your health. Inaccurate measurements can result in misdiagnosis and inappropriate treatments, which might do more harm than good.  

While at-home tests can serve as a useful preliminary tool, it is important to consult a doctor for a definitive diagnosis and appropriate management. Doctors, particularly endocrinologists or urologists, can provide a comprehensive evaluation, considering all relevant factors beyond just the free testosterone levels. They can ensure that tests are conducted under optimal conditions, such as measuring serum total testosterone levels in a fasted state and within the first few hours of waking.³ By seeking professional medical advice, you can avoid the pitfalls of misinterpreted at-home test results and receive the most accurate and effective treatment for your condition.

What each element means

A testosterone test measures separate biomarkers, each affecting testosterone levels in one way or another. Serum total testosterone measures the overall testosterone in your blood. Free testosterone accounts for testosterone not bound to proteins, indicating what's available for use. Prolactin levels can reveal pituitary gland issues. Luteinising hormone (LH) and follicle-stimulating hormone (FSH) help diagnose testicular problems. These are described in greater detail below.

Sex hormone binding globulin

Sex hormone binding globulin (SHBG) is a protein produced by the liver that binds tightly to testosterone, estradiol, and dihydrotestosterone (DHT), transporting them in the blood in an inactive form.⁴ SHBG regulates the transport and activity of these sex hormones, with only 1–2% of them being unbound and biologically active. SHBG levels can influence the availability of free testosterone, with higher levels seen in conditions like pregnancy, ageing, and hyperthyroidism, and lower levels in obesity and hypothyroidism.⁴  

SHBG testing is crucial for investigating conditions like hirsutism in women and infertility or erectile dysfunction in men. Higher levels of SHBG mean that there is less free testosterone available, which can contribute to symptoms of low testosterone. That means your total testosterone levels may appear within range after testing, but your free testosterone levels may be lower, explaining the symptoms you may be experiencing.

Free testosterone

Free testosterone refers to the small fraction of testosterone, around 1–2%, that circulates in the blood unbound to any proteins. Most testosterone is either tightly bound to SHBG or weakly bound to albumin.⁵  

Free testosterone is considered the metabolically active form, meaning that it’s the form of testosterone that is used by the body.⁵ In men, measuring free testosterone is key to identifying androgen deficiency disorders like hypogonadism. In women, it helps diagnose conditions of androgen excess such as polycystic ovary syndrome (PCOS) and hirsutism.⁵

Serum total testosterone

A total testosterone test measures both free testosterone and testosterone bound to proteins such as SHBG and albumin. This combined measurement provides a comprehensive overview of testosterone levels in the body. Total testosterone levels below 10.4 nmol/L may indicate hypogonadism, while levels above 10.4 nmol/L generally considered normal.⁶ However, levels between 8 and 12 nmol/L fall into a grey zone, necessitating further evaluation. In such cases, assessing free or bioavailable testosterone (non-SHBG-bound) is essential for a more accurate diagnosis. ⁶

Prolactin

Prolactin is a hormone primarily known for its role in breast milk production, especially during the third trimester of pregnancy. However, prolactin also plays a significant role in male health. It enhances luteinising hormone (LH) receptors in the testes, which increases testosterone secretion.⁷

Elevated prolactin levels can indicate a prolactinoma, a pituitary gland tumour that produces prolactin.⁸ This condition suppresses LH, leading to low testosterone. Symptoms in men include decreased libido, erectile dysfunction, and gynecomastia, often accompanied by elevated serum prolactin and low testosterone levels.⁸

Prolactin is beneficial for the central nervous system, promoting neuron formation and reducing stress and anxiety. The interaction between prolactin and testosterone is complex, making it essential to consider both when evaluating testosterone levels.⁸

Gonadotropins: Luteinising hormone (LH) and Follicle-stimulating hormone (FSH)

Follicle-stimulating hormone (FSH) and luteinising hormone (LH) are crucial gonadotropins secreted by the anterior pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. These hormones regulate gonadal function by promoting sex steroid production and gametogenesis.⁹

In men, LH stimulates the Leydig cells in the testes to produce testosterone. FSH, on the other hand, is vital for testicular growth and enhances the production of androgen-binding protein by Sertoli cells. This protein ensures high local concentrations of testosterone, essential for spermatogenesis.¹⁰

Elevated FSH levels in men often indicate primary hypogonadism or a gonadotroph adenoma. Rarely, excessive GnRH can lead to pituitary adenomas, causing overproduction of FSH and LH, and consequently, excessive estrogen or testosterone. Low GnRH levels can result in delayed puberty, low sex drive, infertility, and conditions like Kallman syndrome.

It’s important to get it right

Understanding your testosterone levels isn't just about one simple test – it involves looking at multiple elements, each affecting your symptoms in different ways. From total and free testosterone to prolactin, LH, and FSH, these tests offer crucial insights into your hormonal health. That's why it's so important to see a doctor. They can ensure the tests are done correctly and help interpret the results, identifying the root cause of your symptoms. This way, you get the best treatment tailored for you.  

References

1. Nassar GN, et al. Physiology, StatPearls Publishing. 2023; Volume.
2. Boots LR, et al. Fertil Steril. 1998;69(2):286–92.
3. Crawford ED, et al. Curr Med Res Opin. 2015;31(10):1911–4.
4. Sex hormone binding globulin. Sciencedirect.com. [cited 2024 Jun 18]. Available from: https://www.sciencedirect.com/topics/neuroscience/sex-hormone-binding-globulin.
5. Shea JL, et al. In: Advances in Clinical Chemistry. Elsevier; 2014. p. 59–84.
6. Arver S, et al. In: Frontiers of Hormone Research. Basel: KARGER; 2008. p. 5–20.
7. Cheung CY. Endocrinology. 1983;113(2):632–8.
8. Shimon I, et al. Pituitary. 2014;17(3):246–50.
9. Casteel CO, et al. Physiology, Gonadotropin-Releasing Hormone. 2024 [cited 2024 Jun 18]. Available from: https://pubmed.ncbi.nlm.nih.gov/32644418/.
10. Follicle-stimulating hormone abnormalities. Medscape.com. 2024 [cited 2024 Jun 18]. Available from: https://emedicine.medscape.com/article/118810-ove.