Written by Jillian Gordon
Medically reviewed by Dr. Haleem Mohammed, Chief Medical Officer at Gameday Men’s Health
At a Glance
- A CBC blood test measures red blood cells, white blood cells and platelets.
- TRT can increase red blood cell production, so regular CBC testing is an important part of treatment.
- Hemoglobin and hematocrit are two of the key numbers a CBC test will monitor, especially during the first few months of TRT.
- Regular testing helps your clinician catch changes early and adjust your TRT treatment when needed.
When you begin to explore testosterone replacement therapy (TRT) for a suspected testosterone deficiency, having your testosterone checked is an obvious part of the process. But there’s another blood test you’ll soon become familiar with: the complete blood count, or CBC blood test.
A CBC measures different components of your blood, including red blood cells, white blood cells and platelets. While it can provide important information about your overall health, CBC testing is especially important during TRT monitoring because testosterone stimulates red blood cell production.
“Because testosterone makes red blood cells, that's the most common lab side effect we manage,” explains Dr. Haleem Mohammed, MD, MBA, Global Chief Medical Officer of Gameday Men’s Health.
Your local Gameday clinic will check your CBC before starting treatment and continue to monitor it throughout TRT treatment. Here’s a closer look at what your CBC blood test measures and which numbers matter most.
Red Blood Cell Count
Your red blood cell (RBC) count measures the number of red blood cells circulating in your blood. Red blood cells carry oxygen from your lungs to every tissue and organ in the body so they play a pretty important role in your overall health.
Testosterone naturally stimulates red blood cell production, so it’s normal to see your RBC count increase somewhat after starting TRT. Your provider will look at this number alongside hemoglobin and hematocrit to get a better picture of how TRT is affecting your blood.
Hemoglobin
Hemoglobin is the protein inside red blood cells that carries oxygen. Like your red blood cell count, hemoglobin typically rises after starting TRT. According to Dr. Hal, an increase of around 1 to 2 points in hemoglobin may be expected. A drop in hemoglobin, however, deserves a closer look. “Testosterone should push it up,” he says. “If it's going down, I'm looking for blood loss.”
Hematocrit
Of all the numbers on your CBC blood test, hematocrit is one of the most important to monitor during TRT treatment. Hematocrit measures what percentage of your blood is made up of red blood cells. For example, a hematocrit of 45% means that approximately 45% of your blood volume consists of red blood cells.
So why does TRT cause this number to rise?
“Testosterone tells the kidneys to make more erythropoietin, which is the hormone that drives red cell production,” explains Dr. Hal. “It also lowers hepcidin, which frees up more iron for the bone marrow to build red cells.”
When you start TRT, a modest increase in hematocrit is expected. Dr. Hal says many men see their hematocrit rise around 2 to 6 percentage points, with most of the increase occurring during the first three to six months of treatment before leveling off.
But sometimes, hematocrit can become too high. “When hematocrit gets too high, the blood gets thicker, and thick blood theoretically raises clot and stroke risk,” says Dr. Hal, who uses a threshold of 54% as his marker for hematocrit being too high based on AUA guidelines.
However, if your hematocrit reaches 54% or higher, that doesn’t necessarily mean you need to halt TRT. First, your clinician may have you hydrate and repeat the test, since dehydration may temporarily concentrate the blood and make hematocrit appear higher.
If your hematocrit remains elevated, your clinician can look for factors that may be contributing to the increase. These can include a higher testosterone dose, smoking, excess weight, or untreated sleep apnea. Adjusting the dose or splitting it into smaller, more frequent doses may also help stabilize your hematocrit levels.
MCV, MCH, MCHC, and RDW
These four markers provide more information about the size and characteristics of your red blood cells.
- MCV (mean corpuscular volume) measures the average size of your red blood cells. Small red blood cells can be a sign of an iron deficiency, while larger cells may be associated with other nutritional or health issues.
- MCH (mean corpuscular hemoglobin) measures the average amount of hemoglobin inside each red blood cell.
- MCHC (mean corpuscular hemoglobin concentration) measures the concentration of hemoglobin within your red blood cells.
- RDW (red cell distribution width) measures how much your red blood cells vary in size.
If something on your CBC looks off, reviewing these numbers may help paint a clearer picture of what’s actually happening in your body and if your treatment needs to be adjusted.
White Blood Cell Count
White blood cells are a vital part of your immune system and help your body fight infections. Unlike red blood cells, your white blood cell count shouldn’t significantly increase simply during TRT treatment. However, if white blood cells and platelets rise along with red blood cells, Dr. Hal says it might be a sign of something more serious and should be investigated further.
Neutrophils, Lymphocytes and Eosinophils
Speaking of white blood cells, your CBC blood test may also break your white blood cells down into several different types.
- Neutrophils are your body’s first line of defense against many infections, particularly bacterial infections.
- Lymphocytes include immune cells that help your body recognize and fight infections and produce antibodies.
- Eosinophils help fight allergic reactions and certain parasite attacks.
As mentioned, TRT shouldn’t cause major changes to these numbers so any unexpected increase in your levels is worth exploring further.
Platelets
Platelets are tiny cell fragments that help your blood clot when you’re injured. With TRT, your platelet count generally shouldn’t rise simply because you’re taking testosterone. If platelets and white blood cells do increase alongside red blood cells, your provider may want to investigate whether something other than TRT is affecting your blood cell production.
CBC and TRT: What Changes Are Expected?
How does TRT impact your CBC levels? The most expected change is for red blood cells, hemoglobin and hematocrit to rise slightly during the first several months of treatment and eventually level off. White blood cells and platelets should generally remain around their baseline levels throughout TRT.
There are, however, certain changes that deserve a closer look. Dr. Hal pays particular attention to a hematocrit of 54% or higher, hematocrit that continues climbing beyond the first six months, rising white blood cells or platelets, falling hemoglobin, or signs of an iron deficiency.
How Often Should You Get a CBC Blood Test on TRT?
Repeated CBC testing is particularly important early on in treatment since the biggest changes in red blood cell production often happen during the first few months. “I get a CBC at baseline, around three months, around six months, then at least yearly,” says Dr. Hal. After that, your lab schedule may vary depending on your results, TRT dose and other health factors.
Ultimately, regular CBC testing is one of the ways your provider can make sure TRT is doing what it’s supposed to do while catching potential issues early. At Gameday Men’s Health, ongoing lab monitoring helps your care team see how your body is responding and adjust your treatment when needed.
Jillian Gordon, Writer
Jillian Gordon is a Los Angeles-based writer with over a decade of experience covering health and wellness. She has written extensively about longevity science, gut and immune health, nutrition, and emerging wellness trends, with a focus on helping readers make informed decisions about their health.
Dr. Haleem Mohammed, Global Chief Medical Officer
Dr. Haleem Mohammed, MD, MBA, is the Global Chief Medical Officer of Gameday Men’s Health and an award-winning board-certified internal medicine physician specializing in men’s health and performance, including hormone optimization, weight management, erectile performance, peptide and vitamin therapy, musculoskeletal recovery solutions, longevity and precision medicine.
