High Hematocrit: What It Means and What to Do Next
High hematocrit means red blood cells make up a larger share of your blood than usual. Quest's adult reference ranges are 38.5–50.0% for men and 35.0–45.0% for women, but go by the range printed on your report. The most common causes are dehydration, testosterone therapy, smoking, sleep apnea and living at high altitude. A level that stays high on a repeat test should be looked into, because thicker blood raises the risk of blood clots, and a rare bone-marrow condition called polycythemia vera is one of the causes a doctor will want to rule out.
What Causes High Hematocrit?
Dehydration
With less fluid in your blood, the same number of red cells takes up a bigger share, so hematocrit reads high. Not drinking before a morning draw, heavy sweating, vomiting or diarrhea can all do it. It comes back down once you are rehydrated.
Testosterone Therapy
Testosterone stimulates red blood cell production, and a rising hematocrit is its most common lab side effect, especially with injections. Guidelines advise reducing or pausing treatment when hematocrit goes above 54%.
Smoking
Carbon monoxide from smoke lowers how much oxygen your blood can carry, and the body makes extra red cells to compensate. Hematocrit often falls after quitting.
Sleep Apnea and Lung Disease
Repeated drops in oxygen during sleep, or chronic lung disease such as COPD, push the kidneys to release more erythropoietin (EPO), the hormone that tells the bone marrow to make red cells.
High Altitude
Living at high altitude raises hematocrit as a normal adaptation to thinner air. It is not a sign of disease.
Polycythemia Vera
A rare bone-marrow disorder, usually driven by a JAK2 gene mutation, in which the marrow overproduces red cells. White cells and platelets are often high too. It is diagnosed and treated by a hematologist.
Kidney Conditions
Rarely, kidney cysts or tumors, or a kidney transplant, release extra EPO and raise hematocrit.
Medications and Performance Drugs
Anabolic steroids and EPO injections raise hematocrit, sometimes to dangerous levels. Some diabetes drugs (SGLT2 inhibitors such as empagliflozin) cause a small, expected rise.
Associated Symptoms
What to Do Next
1. Retest to confirm
A single abnormal result should be confirmed with a repeat test. Temporary factors like stress, illness, or medications can affect results.
2. Related tests to consider
3. When to see a doctor
If your Hematocrit is significantly abnormal, if you have severe symptoms, or if repeated results confirm the abnormality, consult a healthcare professional for appropriate evaluation and treatment.
Related Conditions
Frequently Asked Questions
This page is for informational purposes only and does not constitute medical advice. Consult a healthcare provider for interpretation of your results.
Content reviewed for accuracy by the JustLabs editorial team.