Why some people on testosterone have more red blood cells
Erythrocytosis Is Rare With Exogenous Testosterone in Gender-Affirming Hormone Therapy.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people take testosterone for gender-affirming care, their bodies sometimes make more red blood cells, which can thicken the blood. This study looked at thousands of people to see how often this happens and what makes it more likely.
Surprising Findings
Hematocrit levels peaked at 45.68% — still within the normal male range — despite testosterone levels reaching 900–949 ng/dL.
Many assume that high testosterone inevitably leads to dangerously high red blood cell counts, but this large study shows even the highest levels stayed within clinical norms.
Practical Takeaways
If you're on testosterone, ask your provider to check your hematocrit regularly — especially if you're using injections.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When people take testosterone for gender-affirming care, their bodies sometimes make more red blood cells, which can thicken the blood. This study looked at thousands of people to see how often this happens and what makes it more likely.
Surprising Findings
Hematocrit levels peaked at 45.68% — still within the normal male range — despite testosterone levels reaching 900–949 ng/dL.
Many assume that high testosterone inevitably leads to dangerously high red blood cell counts, but this large study shows even the highest levels stayed within clinical norms.
Practical Takeaways
If you're on testosterone, ask your provider to check your hematocrit regularly — especially if you're using injections.
Publication
Journal
The Journal of clinical endocrinology and metabolism
Year
2023
Authors
N. Krishnamurthy, Daniel J. Slack, Moira Kyweluk, Olivia Cullen, Jerrica Kirkley, J. Safer
Related Content
Claims (6)
Giving someone testosterone can make their body produce more red blood cells, which thickens the blood; if the blood gets too thick, it might increase the chance of dangerous blood clots.
When people take testosterone as part of gender-affirming care, their blood can get a bit thicker from more red blood cells, but even at its highest, it’s still in a safe, normal range — so serious thickening of the blood is uncommon.
When people take testosterone shots, their blood tends to have more red blood cells than when they use a testosterone patch or gel.
Among people taking testosterone as part of gender-affirming care, most don’t develop dangerously high red blood cell counts — only a small number go above normal levels, so it’s not a common problem.
In men, when their natural testosterone levels go up, their blood tends to carry more red blood cells, making their blood thicker — like going from 42% to 46% red blood cells as testosterone rises.