Testing testosterone the right way

Low testosterone can cause tiredness, low mood, reduced sex drive and loss of muscle. It is also one of the most commonly misread blood tests, because the level moves a lot during the day and from one day to the next.

Test in the morning, fasted

Testosterone peaks in the early morning and can drop by a quarter or more by the afternoon. Eating, especially sugar, lowers it for a few hours. The Endocrine Society 2018 guideline recommends a fasting sample taken in the morning, and LifePrint follows that advice.

One low result is not a diagnosis

Around a third of men with a low first reading are normal when they are tested again. Poor sleep, a hard week, illness or heavy training can all lower testosterone for a while. The guideline asks for a low level to be confirmed on a second morning sample before any conclusion is drawn.

The range LifePrint uses

For adult men, LifePrint uses the harmonised range of 9.2 to 31.8 nmol/L cited by the Endocrine Society. Results between 9.2 and 12 nmol/L sit in a grey zone, where symptoms and free testosterone help decide what it means. For free testosterone, a calculated level below 220 pmol/L supports a low result.

What else to check

• LH and FSH, to see whether the signal from the brain is normal.
• Prolactin, if testosterone is clearly low.
• Blood count, before and during any treatment, because testosterone raises haemoglobin.
• PSA from age 40, before treatment is considered.
• Glucose, HbA1c and lipids, because low testosterone often travels with metabolic health.

If your results come back low, speak to a doctor before starting any supplement or treatment. Many causes can be fixed without hormones, and treatment has risks that need proper monitoring.