While a total testosterone blood test is the first step in diagnosing hypogonadism, it only tells part of the story. To understand why your levels are low and whether the issue originates in the testes or the brain, clinicians in 2026 use a specific panel of additional hormone tests. These secondary markers are essential for distinguishing between primary and secondary hypogonadism and for identifying potentially reversible underlying causes.
What We Will Cover in This Article
- The role of Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH)
- How Sex Hormone Binding Globulin (SHBG) determines active testosterone
- Why Prolactin is a critical marker for pituitary health
- Understanding the diagnostic map for primary vs secondary hypogonadism
- Additional investigations including iron studies and genetic testing
- 2026 clinical protocols for a complete hormonal profile
Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH)
Known as gonadotropins, LH and FSH are the messengers sent from the pituitary gland to the testes. Measuring them is the most important step in categorising the type of hypogonadism you have.
- Luteinising Hormone (LH): This hormone tells the Leydig cells in your testes to produce testosterone. If LH is high but testosterone is low, it suggests Primary Hypogonadism, where the testes are failing. If both LH and testosterone are low, it indicates Secondary Hypogonadism, where the brain is not sending the signal.
- Follicle Stimulating Hormone (FSH): This hormone primarily regulates sperm production. High levels often indicate damage to the tubules where sperm is made, which is particularly relevant if fertility is a concern.
Sex Hormone Binding Globulin (SHBG)
SHBG is a protein produced by the liver that binds to testosterone, making it inactive.
- Variable Factors: SHBG levels can be artificially high due to ageing or liver issues, or low due to obesity and insulin resistance. Without this test, a man with a normal total testosterone level might still have a functional deficiency because too much of his hormone is bound up and unusable.
Prolactin
Prolactin is a hormone produced by the pituitary gland. While primarily associated with breastfeeding in women, high levels in men can actively suppress the production of testosterone.
- The Red Flag: A significantly elevated prolactin level can indicate a non cancerous growth on the pituitary gland, known as a prolactinoma.
- Symptoms: High prolactin is often linked to a severe loss of libido and, in some cases, nipple discharge or breast tissue enlargement. In 2026 protocols, if testosterone is very low and gonadotropins are also low, a prolactin test is mandatory to rule out pituitary issues.
Summary of Diagnostic Markers in 2026
The following table illustrates how these additional tests work together to pinpoint the root cause of hormonal issues.
| Test Marker | Primary Hypogonadism | Secondary Hypogonadism |
| Total Testosterone | Low | Low |
| LH / FSH | High (The brain is shouting) | Low or Normal (The brain is silent) |
| Prolactin | Typically Normal | May be High (suggests pituitary issue) |
| SHBG | Varies by metabolic health | Varies by metabolic health |
Additional Investigations to Consider
Depending on the results of the tests above, a clinician may order further screenings:
- Iron Studies (Ferritin): To check for hemochromatosis, a condition where excess iron deposits in the pituitary or testes, damaging hormone production.
- Pituitary MRI: Only indicated if secondary hypogonadism is confirmed and prolactin is high or testosterone is severely suppressed, often below 5.2 nmol/L.
- Karyotype Testing: A genetic test to rule out Klinefelter Syndrome if primary hypogonadism is detected in a man with small testes.
To Summarise
A single testosterone reading is rarely enough for a clinical diagnosis. By including LH, FSH, SHBG, and Prolactin in your blood panel, your doctor can determine if your low testosterone is caused by a testicular issue or a signalling problem in the brain. In 2026, this comprehensive approach ensures that you receive the correct treatment for your specific type of deficiency, whether that involves hormone replacement or addressing a reversible underlying condition like high prolactin or iron overload.
If you are scheduled for these tests, remember that they must be taken in the morning between 7:00 AM and 10:00 AM while fasted for the most accurate results.
Why do I need an LH test if my testosterone is already low?
Without an LH test, your doctor cannot tell if the problem is in your brain or your testes. The treatment for each is very different.
Can high SHBG be lowered naturally?
In some cases, addressing underlying issues like hyperthyroidism or liver health can help. However, SHBG often increases naturally with age.
Does a high prolactin level always mean I have a brain tumour?
No. Prolactin can be raised by stress, certain medications, or even nipple stimulation. A second test is always performed before a pituitary MRI is considered.
What is the relationship between iron and testosterone?
Excess iron in the blood, a condition called hemochromatosis, is toxic to the organs that produce and regulate hormones. It is a common but often overlooked cause of low testosterone.
Is SHBG tested on the same blood sample as testosterone?
Yes, they can both be measured from the same morning blood draw.
Can FSH be normal even if I have low testosterone?
Yes. FSH and LH are released independently. It is possible to have normal sperm production (normal FSH) but low testosterone (low LH).
Authority Snapshot
This article was written by the MyPatientAdvice clinical team and reviewed by Dr. Stefan Petrov, a UK trained physician with an MBBS and extensive experience in general medicine, surgery, and emergency care. Dr. Petrov has postgraduate certifications including Basic Life Support (BLS), Advanced Cardiac Life Support (ACLS), and the UK Medical Licensing Assessment (PLAB 1 & 2). He is a specialist in medical education and creating evidence based health content. This information follows 2026 clinical protocols for the comprehensive diagnostic evaluation of male hormonal health.
