By Dr. Eric Fete, The Fitness Physician & Muscle Doc, VOTED 2024 TOP 15 MOST INFLUENTIAL HEALTH
EXPERT BY MSN, Cellular Medicine pioneer, Certified Bioidentical Hormone Optimization & testosterone
& weight loss expert and founder of drericprimex.com & primexweightloss.com [Available live in Ohio or
online tele-medicine nationwide]. The Dr Eric Primex Nutrition product line is available at
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I had a patient before that tested high on his red blood cell count after starting TRT for several months & it reminded me that others may experience this side effect too & want to know how to manage it.  Testosterone replacement therapy (TRT) can provide meaningful benefits for men with properly diagnosed testosterone deficiency, but it also requires appropriate medical monitoring. One of the most important potential side effects to watch is erythrocytosis, a condition in which red blood cell production increases and the hematocrit—the percentage of blood made up of red blood cells—rises too high.

Why Does TRT Increase Red Blood Cells?

Testosterone stimulates red blood cell production. This is one reason TRT can increase hemoglobin and hematocrit levels. The effect is well recognized and is considered one of the most common adverse effects of testosterone therapy. 

The response isn't the same for everyone. Dose, testosterone levels, formulation, and individual factors can all influence the increase. Injectable testosterone, particularly shorter-acting injections, has generally been associated with greater increases than some transdermal preparations. 

When Does It Become a Concern?

There isn't a single number that perfectly predicts an individual's risk. However, major professional guidelines use hematocrit as an important safety marker.

The American Urological Association recommends intervention when hematocrit reaches 54% or higher. The Endocrine Society similarly recommends evaluating and addressing erythrocytosis when hematocrit exceeds 54%. 

The important point is that a rising hematocrit shouldn't simply be ignored.

Very high red blood cell levels can increase blood viscosity, and testosterone-associated erythrocytosis has been linked to concern about thrombotic complications. Exactly how much cardiovascular or clotting risk is attributable to a particular hematocrit level remains an area of ongoing research. 

What Should You Do If Your Hematocrit Is High?

The first step isn't necessarily to abandon TRT. Instead, your healthcare professional should determine why your hematocrit is elevated and whether your testosterone treatment needs to be adjusted.

Depending on the situation, this may include:

1. Recheck the blood work.
   Your clinician may repeat the CBC to confirm the result and evaluate hemoglobin and hematocrit together.
2. Review your testosterone dose.
   If testosterone levels are higher than necessary, reducing the dose may help bring hematocrit down. The AUA recommends dose adjustment as a first-line approach when elevated hematocrit occurs alongside high on-treatment testosterone levels. 
3. Evaluate other contributors.
   Smoking, obesity, sleep apnea, chronic low oxygen levels, high altitude, and certain medical conditions can contribute to elevated hematocrit. 
4. Consider the TRT formulation.
   Your clinician may consider changing the dose, dosing interval, or delivery method to reduce large fluctuations in testosterone levels.
5. Discuss therapeutic phlebotomy when appropriate.
   Removing blood can lower hematocrit, but it isn't automatically the best solution for everyone. Current evidence about routine phlebotomy specifically for testosterone-induced erythrocytosis is limited, so the decision should be individualized with your healthcare professional. 

Monitoring Is the Key

A CBC containing hemoglobin and hematocrit should be checked before starting TRT and monitored during treatment. The Endocrine Society recommends checking hematocrit at baseline, 3–6 months after starting therapy, and then annually. 

The goal isn't to achieve the highest possible testosterone level. The goal is to use an appropriate treatment dose while monitoring both benefits and potential adverse effects.

The Bottom Line

Yes, TRT can raise red blood cell production and, in some men, cause hematocrit to become too high. But this is a known and monitorable side effect—not necessarily a reason to avoid TRT altogether.

Proper diagnosis, appropriate dosing, regular CBC monitoring, and evaluation of other causes of elevated hematocrit allow clinicians to manage the issue proactively.

TRT should be optimized—not simply maximized.

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