Is your haematocrit too high?
Role in Red Blood Cell Formation
Testosterone can influence how the body makes red blood cells.
It stimulates the production of erythropoietin, a hormone made by the kidneys that signals the bone marrow to produce red blood cells.
It also acts directly on the bone marrow, encouraging the growth of cells that develop into red blood cells.
As a result, testosterone may lead to higher haematocrit levels — the proportion of red blood cells in the blood.
Effects on Iron Regulation
Testosterone can reduce levels of hepcidin, a hormone that controls how the body absorbs and stores iron.
With lower hepcidin levels, more iron becomes available to the bone marrow, supporting the production of new red blood cells.
This process contributes further to the increase in haematocrit seen in some men on testosterone therapy.
Interaction with Other Hormones
Some testosterone in the body is converted into Oestradiol (a form of oestrogen).
Oestradiol helps maintain the survival and activity of stem cells in the bone marrow — cells responsible for forming blood components, including red blood cells.
This indirect effect may also contribute to higher red blood cell counts.
Androgen Receptor Activation
Testosterone binds to androgen receptors found in various tissues, including the bone marrow.
When activated, these receptors trigger processes that can enhance red blood cell production.
This receptor activity is one of the key reasons testosterone therapy can influence haematocrit levels.
Why Monitoring Matters
Because testosterone can increase red blood cell production, it’s important to monitor haematocrit levels during therapy.
Excessively high levels can thicken the blood, which may increase the risk of complications such as blood clots.
Regular blood tests allow early detection and safe management if levels rise too high.
Managing High Haematocrit
Doctors may use several strategies to help maintain safe haematocrit levels:
Adjusting the testosterone dose to reduce stimulation of red blood cell production
Switching to a different formulation, such as a gel or patch, which may have less effect on haematocrit
Scheduling regular blood tests to monitor haematocrit and haemoglobin
Phlebotomy (blood removal) in cases of significantly high levels
Reviewing the ongoing need for therapy and balancing benefits against risks
Encouraging adequate hydration to prevent blood concentration
This information is provided for educational purposes only and does not replace professional medical advice, diagnosis, or treatment.
Testosterone therapy should only be prescribed and monitored by an AHPRA-registered medical practitioner following a comprehensive medical assessment.
Individual responses vary; always consult your doctor for advice tailored to your specific health needs.