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TRT and High Haematocrit: Managing Thickened Blood on Testosterone Replacement Therapy

At our clinic, we’re proud to support men on testosterone replacement therapy (TRT) — helping you regain energy, confidence, and quality of life.

Testosterone and haematocrit levels

As part of safe and effective TRT, we also monitor key markers like haematocrit, the percentage of red blood cells in your blood.

Why monitor for high haematocrit? Because testosterone can increase red blood cell production — a known and well-documented effect called erythrocytosis. If haematocrit rises too much, your blood can become more viscous, potentially increasing the risk of cardiovascular or thrombotic events (like clots or strokes) [1,2].

Why we monitor for high levels of haematocrit

Several studies have shown that injectable testosterone in particular can significantly raise haematocrit levels [1,3]. This doesn’t happen to everyone, but it’s common enough to watch closely. A large 2022 study found that men on TRT who developed polycythaemia (haematocrit ≥54%) had a higher risk of serious cardiovascular events and blood clots than those who didn’t [2].

Importantly, the increased risk wasn’t seen in men on TRT whose haematocrit remained within safe ranges — reinforcing why regular monitoring is so important.

Managing raised haematocrit on TRT

When haematocrit rises, treatment optimisation is always considered first. In some cases, therapeutic venesection (phlebotomy) or giving blood may help bring levels down more quickly.

Some men on TRT may still be eligible to donate blood through NHS blood services, although eligibility is determined by the blood service and donation should not be viewed as treatment for TRT-induced erythrocytosis.

Many of our patients have found venesection or blood donation helpful, and it can be an effective way to reduce haematocrit levels in the short term.

That said, evidence on the long-term effectiveness of repeated blood removal is mixed. One study found that even with regular donations, a significant number of TRT patients still had elevated levels at follow-up [6]. Another review pointed out that phlebotomy might stimulate the body to produce even more red cells afterward [5].

TRT and giving blood

So, while it’s not a perfect or permanent fix, we view carefully monitored management — which may include treatment optimisation, therapeutic venesection or, where appropriate, blood donation — as a reasonable approach when haematocrit is elevated.

How to lower haematocrit on TRT without donating blood

We don’t believe in a one-size-fits-all approach.

Instead, we look at your labs, symptoms, medical history, and therapy goals. If your haematocrit is approaching or above 52–54%, we’ll walk you through the options: adjusting your testosterone dose, changing injection frequency, and reviewing other contributing factors (like sleep apnoea).

Treating high haematocrit

Our goal is simple: help you get the most from your therapy while keeping your health risks low. With regular check-ins and individualised decisions, we believe TRT can remain both effective and safe.

Do you have questions on haematocrit and testosterone? Let’s talk.

If you’ve recently had bloodwork done or you’re wondering whether therapeutic venesection or blood donation may be appropriate in your case, please don’t hesitate to reach out. We’re here to support you every step of the way.

References

  1. Nolan BJ, et al. Intern Med J. 2021. PMID: 32237098
  2. Ory J, et al. J Urol. 2022. PMID: 35050717
  3. Jones SD Jr, et al. Sex Med Rev. 2015. PMID: 27784544
  4. Drinka PJ, et al. J Am Geriatr Soc. 1995. PMID: 7636099
  5. Bond P, et al. Endocr Connect. 2024. PMCID: PMC11466264
  6. Chin-Yee B, et al. Transfusion. 2017. PMID: 28150363

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