Erythrocytosis refers to thickening of the blood due to increased red blood cell production. The thickness of the blood is measured with a blood test for haematocrit, which is an estimated percentage by volume of red blood cells in the blood.
The effect of testosterone on haematocrit
Testosterone increases the production of red blood cells by the body, which can increase the thickness of the blood. This accounts for why cis men tend to have a higher haematocrit than cis women. Accordingly, exogenous testosterone in masculinising hormone treatment can be associated with increased haematocrit.
Erythrocytosis
In the majority of cases, masculinising hormone treatment in trans men increases the haematocrit to levels usually considered healthy in cis men.
Sometimes, however, masculinising hormone treatment in trans men can thicken the blood further, so that the haematocrit rises above the levels usually considered healthy in cis men. A recent study suggested that polycythaemia can affect around 11% of trans men. The risk of erythrocytosis appears to be highest in the first year of treatment and also appears to be higher with higher doses of testosterone.
Erythrocytosis is a potential concern because it may be associated with an increased risk of blood clots, heart attacks, and strokes.
For this reason, it is recommended that people who are taking testosterone have blood tests to check their haematocrit regularly.
What to do if the haematocrit level indicates erythrocytosis
If your haematocrit is raised above 53%, then this indicates erythrocytosis.
In this case, it is recommended that you discontinue testosterone temporarily. This is to prevent further elevation of haematocrit, which could increase the risk of a blood clot or stroke.
It is advised that you remain well-hydrated, as dehydration can contribute to raised haematocrit.
It is advised that you consult your doctor, who may investigate other potential causes of erythrocytosis. These include smoking, being overweight, obstructive sleep apnoea, and chronic lung conditions. Hence, the overall risk of erythrocytosis can be reduced by stopping smoking, maintaining a healthy body weight, and optimising treatment for any relevant medical conditions.
After undertaking the above, it is advised that you have a repeat blood test in three months to recheck your haematocrit. If your haematocrit has decreased below 53%, then it is safe to recommence testosterone.
After recommencing testosterone, it is recommended that you continue regular checking of your haematocrit to monitor for any recurrence of erythrocytosis.
To use the finger prick test, you need to be 16 or older and not taking spironolactone. Vitall, the service provider, will send your blood test results directly to your email address.
If you’re taking spironolactone, you’ll need an intravenous blood sample. You can get this through an online blood test service of your choosing, through your GP if they’re willing to help, or at a private clinic/hospital.
If you need a Blood Test Referral Letter to advise your GP or healthcare provider, you can purchase one through the Treatment Recommendation form for £20 or order it separately here. The letter explains why you need blood tests and which ones you’ll need to get.
When you have your results, please submit them in the Treatment Recommendation form for analysis.