Diagnosing low testosterone in men: why two morning blood tests matter

Recognised features of testosterone deficiency include reduced sexual desire, fewer spontaneous erections, loss of body hair, small testes, reduced muscle bulk, low bone density and hot flushes. Others, such as tiredness, low mood, poor concentration and weight gain, are common and have many causes, including depression, sleep apnoea, thyroid disease, alcohol and chronic illness. For this reason, professional guidance emphasises confirming biochemical deficiency before concluding that symptoms are due to low testosterone.

Total testosterone measured in the morning is the usual first test. If the result is borderline, or if conditions affecting sex hormone binding globulin are present, such as obesity, diabetes, liver disease or ageing, free testosterone or SHBG may be measured. A low result should be repeated on another morning, because levels vary between days. Laboratories use reference ranges, and clinical practice guidelines from endocrine and sexual medicine societies describe thresholds that clinicians apply together with symptoms.

• Take the sample early, usually before mid-morning, and following local instructions about fasting.

• Avoid having tests during an acute illness, after heavy exercise or after poor sleep, as results may be falsely low.

• Tell the clinician about all medicines and supplements, including steroids and opioids.

• Expect a repeat test if the first is low.

If testosterone is confirmed low, luteinising hormone and follicle-stimulating hormone are measured. High values suggest a testicular cause, such as previous injury, mumps, chemotherapy or genetic conditions. Low or normal values suggest a pituitary or hypothalamic cause or functional suppression due to obesity, illness, opioids or anabolic steroids. Prolactin, iron studies and sometimes pituitary imaging are used where indicated. Identifying the cause matters, because some are treatable.

• Obesity and metabolic syndrome, where weight loss can raise testosterone.

• Obstructive sleep apnoea.

• Type 2 diabetes.

• Opioid and corticosteroid use.

• Alcohol excess and liver disease.

• Depression and chronic stress.

• Anabolic steroid or testosterone use, which suppresses natural production.

Direct-to-consumer panels, finger-prick kits and tests at random times can give misleading results. Treating borderline readings with replacement without confirming deficiency or considering alternatives exposes men to unnecessary risks. Age-related decline in testosterone is gradual and modest, and low-normal levels in an older man with no specific symptoms do not necessarily need treatment.

A clinician will review lifestyle contributors, medicines and associated conditions and discuss whether treatment is appropriate. Testosterone replacement is considered when deficiency is confirmed and symptomatic, taking into account fertility wishes, prostate health, blood count, heart disease and sleep apnoea. Some men benefit from addressing weight, sleep and alcohol first. Referral to an endocrinologist is advised when the cause is unclear or the picture is complex.