Short answer: Testosterone raises red blood cell mass, so hematocrit (the share of your blood made of red cells) usually goes up on TRT. The Endocrine Society guideline says to check it at baseline, 3 to 6 months after starting, and then yearly, and to stop therapy if it rises above 54% until it falls to a safe level. The Xyosted label asks for a check about every 3 months. In Xyosted's trials, mean hematocrit rose 3.8 points at 6 months and 5.4 points at 1 year, and 4.2% of men reached 55% or more.
Of all the routine labs on testosterone therapy, hematocrit is the one most likely to force a change in plan. This article explains what it measures, the thresholds in the main US guideline, what the drug labels say, and what studies show about injection type. It does not give dosing advice. We cover cycle timing for testosterone draws in a separate post on TRT steady state, and what else to log in our TRT symptom tracker guide.
Hematocrit is the percentage of your blood volume made up of red blood cells. Testosterone stimulates red cell production. The Xyosted label puts it plainly: "Increases in hematocrit reflective of increases in red blood cell mass may require discontinuation." The Depo-Testosterone label lists polycythemia (too many red cells) among hematologic side effects and says hemoglobin and hematocrit "should be checked periodically" during long-term use.
The concern is that thicker blood may raise the risk of clots. The Xyosted label states: "An increase in red blood cell mass may increase the risk of thromboembolic events."
The 2018 Endocrine Society guideline on testosterone therapy (Bhasin et al.) gives the clearest numbers:
The guideline also notes that erythrocytosis is more frequent in older men than in younger men, and its comparison of formulations lists "less erythrocytosis than injectable T" as a feature of transdermal gels.
Xyosted is an FDA-approved testosterone enanthate autoinjector given under the skin once a week. Its label has unusually detailed numbers because it comes from recent trials:
The label also carries a boxed warning on blood pressure: ambulatory monitoring found average increases of 3.9/1.5 mm Hg after 12 weeks. Blood pressure is worth logging alongside hematocrit.
Note the schedules differ. The Xyosted label says about every 3 months for that product. The Endocrine Society guideline, written for all formulations, says baseline, 3 to 6 months, then yearly. Your clinician sets the actual plan.
A separate 26-week study of the same autoinjector in 133 men gives a second look at early changes (Gittelman 2019). Hematocrit of 52% or higher was the most frequently reported adverse drug reaction, in 10 men (7.5%). Clinic blood pressure rose by an average of 3.4/1.8 mm Hg by week 26, and 24-hour monitoring at week 12 showed average rises of 3.7/1.3 mm Hg. In the one-year label study, 10% of men either started blood pressure medication or had it changed. These are the kinds of shifts that only show up if someone is measuring them on a schedule.
The evidence comparing routes and schedules is limited:
We cover route in more detail in subcutaneous vs intramuscular testosterone, and frequency in weekly vs twice-weekly injections. No trial we found shows that changing frequency alone lowers clot or heart risk.
The TRAVERSE trial randomized 5,246 men aged 45 to 80 with heart disease or high heart risk to testosterone gel or placebo. Testosterone was noninferior to placebo for major heart events (7.0% vs 7.3%), but the testosterone group had a higher incidence of atrial fibrillation, acute kidney injury and pulmonary embolism (Lincoff 2023). TRAVERSE used a gel, not injections, and was not designed around hematocrit, but it is a reminder that clot risk on testosterone is real enough to monitor.
Dose Track lets you log each injection, add lab results such as hematocrit, hemoglobin and blood pressure, and see them on one timeline with the dose history that came before. That makes the 3-to-6-month conversation with your prescriber faster and more concrete.
Questions about the app? See the help center or join the Dose Track community.
Every number in this article comes from one of these sources, checked on October 22, 2026. This article is for education. It is not medical or legal advice, and nothing here is a dose recommendation.