What Is Hematocrit?
Hematocrit is the percentage of your blood made up of red blood cells. Red blood cells carry oxygen throughout your body. A normal hematocrit for adult men is roughly 41% to 50%, though ranges vary slightly by lab.
Why Does TRT Raise Hematocrit?
Testosterone stimulates the bone marrow to produce more red blood cells. It also affects iron regulation in a way that makes more iron available for making red blood cells.
As a result, a rise in hematocrit—called erythrocytosis—is the most common lab change in men on testosterone therapy. It's more likely with:
- Injections, especially higher doses given less frequently
- Older age
- Smoking
- Untreated sleep apnea
- Living at high altitude
Is High Hematocrit Dangerous?
When hematocrit rises too high, blood becomes thicker, which may increase the risk of blood clots. Because of this, guidelines recommend:
- Checking hematocrit before starting TRT
- Rechecking at around 3 to 6 months, then periodically
- Pausing or adjusting treatment if hematocrit rises above about 54%
Symptoms of very high hematocrit can include headaches, dizziness, flushed skin, or fatigue, though many men have no symptoms.
How Providers Manage It
- Lower the dose or increase frequency: Smaller, more frequent injections reduce peaks
- Switch formulations: Gels or other forms may raise hematocrit less
- Blood donation: Donating blood can lower hematocrit (if you're eligible to donate)
- Treat sleep apnea if present
- Stop smoking
- Stay hydrated, since dehydration can make hematocrit look higher
Why Regular Labs Are Essential
High hematocrit is easy to catch and manage with routine blood work. It's one of the main reasons TRT should always be done under medical supervision.
Learn more about provider-guided testosterone therapy here: Heva Hormone Optimization
The Bottom Line
Rising hematocrit is common on TRT and usually manageable. Regular monitoring and simple adjustments help keep your blood healthy and your treatment safe.