When to start Testogel is a critical clinical decision that requires confirmed biochemical hypogonadism alongside relevant symptoms. Testogel, a transdermal testosterone replacement therapy licensed in the UK, should only be initiated after at least two morning blood tests demonstrate consistently low serum testosterone levels (typically below 12 nmol/L) and reversible causes have been excluded. Before starting treatment, comprehensive pre-treatment assessment including baseline blood tests, prostate evaluation, and cardiovascular risk stratification is mandatory. This article provides evidence-based guidance on clinical indications, pre-treatment investigations, dosing protocols, and monitoring requirements to ensure safe and effective testosterone replacement therapy.

What Is Testogel and How Does It Work?

Testogel is a transdermal testosterone replacement therapy (TRT) licensed in the UK for the treatment of male hypogonadism. It is a clear, colourless hydroalcoholic gel containing testosterone as the active pharmaceutical ingredient. Two formulations are available: Testogel 50 mg in 5 g (1%) sachets and Testogel 16.2 mg/g pump dispenser (each pump actuation of 1.25 g delivers 20.25 mg of testosterone). The gel is applied topically to clean, dry skin—on the shoulders and upper arms for both formulations, with the abdomen also permitted for the 1% sachet product—where it is absorbed through the dermal layers into the systemic circulation.

The mechanism of action involves the transdermal delivery of exogenous testosterone, which supplements or replaces endogenous production when the body's natural testosterone levels are insufficient. Once absorbed, testosterone binds to androgen receptors in target tissues throughout the body, including muscle, bone, adipose tissue, and the central nervous system. This binding initiates a cascade of physiological effects that restore normal androgenic function.

Testosterone plays crucial roles in maintaining muscle mass and strength, bone mineral density, libido and sexual function, mood regulation, and metabolic processes including fat distribution and erythropoiesis. The gel formulation offers several advantages over other TRT modalities: it provides relatively stable serum testosterone concentrations throughout the day, avoids first-pass hepatic metabolism, and allows for dose adjustments based on individual response.

The alcohol carrier in Testogel evaporates quickly after application, leaving testosterone on the skin surface for gradual absorption. Pharmacokinetic profiles vary by formulation; prescribers should consult the relevant Summary of Product Characteristics (SmPC) for specific details. This makes Testogel a convenient and effective option for long-term testosterone replacement in appropriately selected patients.

When to Start Testogel: Clinical Indications

The decision to start Testogel should be based on confirmed biochemical hypogonadism accompanied by relevant clinical symptoms. According to guidance from the British Society for Sexual Medicine (BSSM) and consistent with NICE Clinical Knowledge Summaries, testosterone replacement therapy is indicated when a man presents with symptoms of testosterone deficiency alongside consistently low serum testosterone levels on at least two separate morning blood tests.

Clinical features that may warrant investigation for hypogonadism include reduced libido, erectile dysfunction, decreased energy and fatigue, loss of muscle mass and strength, increased body fat (particularly central adiposity), reduced bone mineral density or osteoporosis, mood disturbances including depression or irritability, and cognitive difficulties such as poor concentration. It is important to recognise that these symptoms are non-specific and can result from numerous other medical conditions, lifestyle factors, or normal ageing.

Biochemical hypogonadism is typically defined as a total testosterone level below 12 nmol/L, though some guidelines suggest a lower threshold of 8 nmol/L for definitive diagnosis. Borderline cases (testosterone 8–12 nmol/L) require careful clinical correlation with symptoms and may benefit from measurement of free or bioavailable testosterone, sex hormone-binding globulin (SHBG), and luteinising hormone (LH) to distinguish primary from secondary hypogonadism. Reference ranges vary between laboratories, and results should always be interpreted in the clinical context.

Testogel may be initiated for primary hypogonadism (testicular failure due to genetic conditions, chemotherapy, radiation, trauma, or infection) or secondary hypogonadism (hypothalamic-pituitary dysfunction). However, it is essential to identify and address reversible causes of low testosterone—such as obesity, type 2 diabetes, obstructive sleep apnoea, excessive alcohol consumption, certain medications (particularly opioids and glucocorticoids), acute illness, and chronic disease—before committing to lifelong TRT. Testosterone levels should be re-tested once the patient is well and any reversible factors have been addressed. In younger men of reproductive age, referral to endocrinology is advisable to preserve fertility options and to investigate underlying causes of secondary hypogonadism.

Pre-Treatment Assessment and Blood Tests Required

Before starting Testogel, a comprehensive clinical assessment and baseline investigations are mandatory to confirm the diagnosis, exclude contraindications, and establish a reference point for monitoring. The initial evaluation should include a detailed medical history focusing on symptoms of hypogonadism, sexual function, fertility concerns, cardiovascular risk factors, previous or current prostate disease, sleep disturbances, and medication use.

Physical examination should assess body mass index (BMI), blood pressure, gynaecomastia, testicular volume (using an orchidometer), signs of androgen deficiency (reduced body hair, decreased muscle mass), and a digital rectal examination (DRE) in men over 50 years or those with lower urinary tract symptoms to evaluate prostate size and detect abnormalities.

Essential baseline blood tests include:

• Serum total testosterone: measured on at least two occasions between 07:00–11:00 hours when levels are physiologically highest

• Sex hormone-binding globulin (SHBG): to calculate free or bioavailable testosterone if total testosterone is borderline

• Luteinising hormone (LH) and follicle-stimulating hormone (FSH): to differentiate primary from secondary hypogonadism

• Prolactin: elevated levels may indicate a pituitary adenoma requiring further investigation

• Full blood count (FBC): to establish baseline haemoglobin and haematocrit, as testosterone stimulates erythropoiesis

• Prostate-specific antigen (PSA): baseline assessment in men aged 40 years and over, as advised in the Testogel SmPC and local protocols (measured in micrograms per litre, µg/L)

• Liver function tests (LFTs) and lipid profile: to assess cardiovascular risk and hepatic function

• HbA1c or fasting glucose: particularly in men with metabolic syndrome or obesity

• Thyroid function tests (TFTs): to exclude thyroid dysfunction as a cause of symptoms

• Iron studies (serum ferritin, transferrin saturation): to screen for haemochromatosis, particularly if secondary hypogonadism is suspected

Additional investigations may include bone density scanning (DEXA) if osteoporosis is suspected, and pituitary imaging (MRI) if secondary hypogonadism is confirmed with elevated prolactin, very low testosterone with inappropriately low or normal LH/FSH, or symptoms suggestive of pituitary disease (headaches, visual disturbances). Clear referral triggers to endocrinology include markedly raised prolactin, suspected pituitary pathology, or desire for fertility preservation. This thorough pre-treatment assessment ensures that Testogel is initiated safely and appropriately.

Starting Testogel: Dosage and Application Guidelines

Testogel should be initiated at the lowest effective dose, with subsequent titration based on clinical response and serum testosterone levels. Dosing and application instructions are formulation-specific and must follow the relevant Summary of Product Characteristics (SmPC).

For Testogel 16.2 mg/g pump dispenser:

• Starting dose: 20.25 mg of testosterone (one pump actuation) applied once daily

• Titration: may be increased in increments of 20.25 mg to a maximum of 81 mg daily (four pump actuations) based on serum testosterone levels and clinical response

• Application sites: shoulders and upper arms only

• Wash-off time: avoid washing the application area for at least 2 hours after application

For Testogel 50 mg in 5 g (1%) sachet:

• Starting dose: 50 mg of testosterone (one sachet) applied once daily

• Titration: may be adjusted between 25 mg and 100 mg daily (half to two sachets) based on serum testosterone levels and clinical response

• Application sites: shoulders, upper arms, or abdomen

• Wash-off time: avoid washing the application area for at least 6 hours after application

Application technique is crucial for optimal absorption and to minimise the risk of transfer to others:

• Apply to clean, dry, intact skin—never to the genital area

• Spread the gel thinly over a large surface area and allow it to dry for 3–5 minutes before dressing

• Wash hands thoroughly with soap and water immediately after application

• Cover the application site with clothing once dry to prevent inadvertent transfer to partners or children

• Avoid showering or swimming until the formulation-specific wash-off time has elapsed

• Rotate application sites to prevent skin irritation

Patients must be counselled about the risk of testosterone transfer through skin-to-skin contact. Direct contact with the application site should be avoided until the gel has dried completely and the area is covered. If contact occurs, the affected person should wash the area immediately with soap and water. This is particularly important for women and children, in whom inadvertent testosterone exposure can cause virilisation or premature sexual development.

Dose adjustments are typically made after 4–12 weeks based on serum testosterone levels. The timing of blood sampling should follow the SmPC guidance for the specific formulation used. The goal is to achieve testosterone levels within the mid-normal adult male reference range for the local laboratory. Patients should be advised that symptomatic improvement may take several weeks to months, particularly for sexual function, mood, and body composition changes.

Monitoring and Follow-Up After Starting Treatment

Systematic monitoring after initiating Testogel is essential to ensure therapeutic efficacy, detect adverse effects, and adjust dosing appropriately. The British Society for Sexual Medicine recommends a structured follow-up schedule with both clinical assessment and biochemical monitoring at defined intervals.

Initial monitoring should occur at 3 months after starting treatment. This visit should include:

• Clinical review of symptom improvement (libido, energy, mood, erectile function)

• Serum testosterone level: timing of blood sampling should follow the SmPC guidance for the specific formulation used, aiming for the mid-normal adult male reference range for the local laboratory

• Full blood count: to monitor haemoglobin and haematocrit (testosterone stimulates red blood cell production)

• Liver function tests: if clinically indicated or if there are pre-existing hepatic concerns

If testosterone levels are not within the target range, dose adjustment should be made and reassessment performed after a further 3 months. Once stable therapeutic levels are achieved with symptomatic improvement, monitoring intervals can be extended to 6–12 months.

Long-term monitoring (annually once stable) should include:

• Serum testosterone: to confirm ongoing therapeutic levels within the normal adult male range

• Full blood count: haematocrit ≥0.54 (54%) warrants dose reduction or temporary cessation due to increased cardiovascular and thrombotic risk; venesection may be considered if clinically appropriate

• PSA and digital rectal examination: in men aged 40 years and over; a PSA rise greater than 1.4 µg/L within 12 months, an abnormal DRE finding, or PSA above age-specific thresholds requires urological referral

• Lipid profile and HbA1c: to assess cardiovascular and metabolic parameters

• Bone density scanning: if indicated, particularly in men with osteoporosis at baseline

Patients should contact their GP urgently if they experience chest pain, leg swelling, shortness of breath (possible thromboembolism), lower urinary tract symptoms, prolonged or painful erections, mood changes, or signs of skin irritation at application sites. The MHRA advises vigilance for venous thromboembolism during testosterone therapy. Patients should also be advised to report any suspected side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. Regular review ensures that Testogel therapy remains safe, effective, and appropriately tailored to individual needs.

Who Should Not Start Testogel: Contraindications

Testogel is contraindicated in several clinical scenarios where testosterone replacement poses significant health risks. Understanding these contraindications is crucial for safe prescribing and patient selection.

Absolute contraindications (as per the UK Summary of Product Characteristics) include:

• Known or suspected carcinoma of the prostate or male breast (current or previous)

• Hypersensitivity to testosterone or any of the gel excipients

• Use in women or children: Testogel is not indicated for use in women or children and is contraindicated in these populations

Conditions requiring careful risk-benefit assessment and close monitoring (cautions) include:

• Severe cardiac, hepatic, or renal insufficiency: testosterone may cause fluid retention and exacerbate these conditions

• Untreated obstructive sleep apnoea: testosterone may worsen apnoea severity

• Benign prostatic hyperplasia with significant lower urinary tract symptoms: testosterone may exacerbate urinary obstruction

• Elevated haematocrit (0.50–0.54): requires close monitoring if treatment proceeds; haematocrit ≥0.54 is a reason to withhold or reduce treatment

• Uncontrolled hypertension or significant cardiovascular disease: recent data suggest possible increased cardiovascular risk, though evidence remains debated; careful patient selection and monitoring are advised

• Elevated PSA or abnormal digital rectal examination findings: require full urological evaluation before initiating TRT

• Desire for fertility: testosterone suppresses gonadotrophin secretion, reducing spermatogenesis; alternative treatments (e.g., human chorionic gonadotrophin) should be considered in men wishing to conceive, and endocrinology referral is recommended

Testogel should be used with caution in elderly men, who have higher baseline cardiovascular and prostate cancer risk. The MHRA advises careful patient selection and monitoring in this population, including awareness of venous thromboembolism risk.

Before starting Testogel, prescribers must thoroughly evaluate each patient's medical history, conduct appropriate investigations, and ensure that no contraindications exist. When cautions are present, shared decision-making with the patient—weighing potential benefits against risks—is essential. Regular monitoring can mitigate some risks, but absolute contraindications preclude Testogel use entirely.

Frequently Asked Questions