TSH level in men

This test measures how much thyroid-stimulating hormone is in your blood, in milli-units per litre (mE/L). Your pituitary makes TSH and sets the pace of the thyroid with it, and the thyroid then produces T4 and T3, the hormones that keep your metabolism up to pace.

The feedback is log-linear: a small fall in free T4 produces a much larger rise in TSH, which makes this the most sensitive first test. The direction is counter-intuitive. If the thyroid runs slow, the pituitary pulls harder and the number climbs; with too much hormone the signal switches off instead. A high value therefore means an underactive thyroid, and with an overactive one the number sits low.

For men the link with the sex hormones is the most interesting part. The thyroid also drives the binding protein SHBG, the protein that holds testosterone in the blood. With an overactive thyroid SHBG rises, so more of your testosterone becomes bound and your total testosterone can look normal while the free fraction disappoints; with an underactive thyroid the reverse often happens.

That is the practical reason to measure both. Disappointing energy alongside a perfectly good testosterone is a classic reason to add free T4.

Men who investigate energy, libido or body composition almost always start with testosterone. That is logical, but it leaves a common explanation on the table, because an underactive thyroid produces nearly the same pattern of complaints: fatigue, less interest in sex, slower recovery, cold hands and slowly climbing weight. If only testosterone is measured and it is normal, the question stays unanswered.

The two sides of the thyroid feel different. With an underactive thyroid energy is heavy and slow to start with daytime sleepiness, resting heart rate sits lower than you are used to, you feel cold quickly, weight climbs slowly, muscle aches and slow recovery occur, and SHBG is often lower. With an overactive thyroid you are wired but exhausted, resting heart rate sits higher and the heart sometimes skips, you tolerate heat poorly and sweat, weight falls on normal intake, you lose strength, especially in the legs, and SHBG rises so the free testosterone fraction falls.

One misunderstanding deserves emphasis. Many men read a low value as favourable, as though the thyroid were then running efficiently, and the opposite is true: a lowered TSH usually means the thyroid makes too much hormone, and that comes with a high resting heart rate, poor sleep and loss of muscle mass. For strength and recovery that is unfavourable.

Sleep debt and chronic stress belong in this story too. They shift the daily rhythm of TSH and disturb your testosterone at the same time, so a single measurement during a bad stretch is worth little.

Have TSH measured when energy, libido or recovery structurally disappoint, and particularly when your testosterone has already been measured and came back normal; the thyroid is then the most obvious next step. Other reasons are a resting heart rate that changes without cause, cold hands and feet, unexplained weight gain, or thyroid disease in the family.

Timing matters more than it does for testosterone. TSH is highest overnight and dips in the early afternoon, with variation of roughly 31 percent across a day. So give blood in the morning and around the same hour when repeating, which works out well because testosterone follows the same rule.

Do not measure during or just after a spell of illness, and wait a few weeks after a period of severe sleep deprivation too, because both shift the axis.

Combine TSH with free T4 in the same draw. If the complaint persists with a normal TSH and a normal free T4, free T3 can add information, and with a persistently raised value anti-TPO is the logical next step.