Writer: Jillian Foglesong Stabile, MD, FAAFP, DABOM
Hematocrit (HCT) is an important marker measured in a complete blood count (CBC)—a routine blood test that offers critical insights into your overall health. If you’ve received your lab results and are wondering what your hematocrit number means, you’re not alone.
In this guide, we’ll discuss the HCT blood test, normal range, and what your hematocrit level means. You’ll also learn how lifestyle, hydration, altitude, and medical conditions can influence this value—and what you can do about it.
What Is Hematocrit (HCT)?
Hematocrit is the percentage of your blood that is made up of red blood cells (RBCs), the cells responsible for carrying oxygen from your lungs to tissues throughout the body. It’s typically measured as part of a complete blood count, or CBC, and provides valuable information about blood volume and oxygen-carrying capacity. [1]
For example, a hematocrit of 44% means that 44% of your blood volume consists of red blood cells, with the rest made up of plasma, white blood cells, and platelets.
Why Is Hematocrit Tested?
An HCT test may be ordered:
- To assess for anemia or polycythemia
- To monitor chronic conditions such as kidney disease or heart disease
- As part of routine wellness checks or pre-surgical evaluations
- To evaluate hydration status or blood loss
A low or high hematocrit can affect your body’s ability to deliver oxygen effectively and may signal an underlying health issue. [2,3]
What Is the Normal Range for HCT?
The normal range for hematocrit depends on age, sex, and biological factors. The U.S. National Library of Medicine provides the following general reference values [4]:
| Population | Normal Hematocrit Range |
|---|---|
| Adult men | 41%–50% |
| Adult women | 36%–44% |
| Children (1–10 yrs) | 32%–44% |
| Newborns | 55%–68% |
Your healthcare provider will help you interpret your results in the context of your overall health status, taking into account factors such as hydration, elevation, pregnancy, and other individual variables.
What Causes Low Hematocrit?
A low hematocrit level means there are fewer red blood cells than expected. This may indicate that your body is not producing enough RBCs or is losing them faster than they can be replaced.
Possible Causes of Low HCT
There are many possible causes for abnormalities in HCT, including [5,6]:
- Iron-deficiency anemia
- Vitamin B12 or folate deficiency
- Chronic kidney disease, which can suppress erythropoietin production
- Heavy menstrual bleeding
- Gastrointestinal blood loss
- Bone marrow disorders (eg, aplastic anemia or leukemia)
There may be other potential causes of low HCT as well. Your healthcare provider can help you determine if other causes could contribute to the low levels.
Symptoms of Low HCT
Low HCT may be asymptomatic or may have symptoms, including [5]:
- Fatigue or weakness
- Pale skin
- Dizziness or shortness of breath
- Cold hands and feet
These symptoms can often be associated with other health conditions, so it is important to talk to your healthcare provider about whether your symptoms are related to low HCT or other potential reasons.
What Causes High Hematocrit?
A high hematocrit level indicates a greater-than-normal proportion of red blood cells in the blood. This can thicken the blood and increase the risk of clotting and cardiovascular strain.
Common Causes of Elevated HCT
When HCT levels are elevated, there are several potential causes [7,8]:
- Dehydration (reduced plasma volume)
- Living at high altitudes (compensatory RBC production)
- Smoking
- Chronic lung disease or hypoxia (such as obstructive sleep apnea)
- Polycythemia vera, a rare bone marrow disorder
These are the most common potential causes of elevated hematocrit, but the list is not exhaustive. Your healthcare provider can help you determine if other conditions may be the cause.
Potential Risks of High HCT
An elevated HCT can have potentially serious health impacts, including[7]:
- Blood clots
- Stroke
- Heart attack
- Headaches or blurred vision
What Level of HCT Is Concerning?
While reference ranges provide a general guide, levels significantly outside the range—especially when paired with symptoms—may require follow-up. [8]
- Below 30%: Typically considered clinically low in adults
- Above 55%: Considered high and may require evaluation for polycythemia or dehydration
If you’re symptomatic or have additional abnormal blood markers, your healthcare provider may order further testing or refer you to a hematologist. It’s important to note that these levels are just guidelines and that your healthcare provider may recommend additional evaluation or treatment at other levels depending on your unique health needs.
Factors That Can Affect HCT Levels
Not all abnormal results mean you’re ill. There are other factors that can impact your HCT levels. Hematocrit can vary based on[4]:
- Sex and hormones: Testosterone increases RBC production
- Altitude: Higher elevations increase erythropoiesis
- Hydration: Dehydration can falsely elevate hematocrit
- Pregnancy: Increases plasma volume, lowering HCT
- Medications: Such as chemotherapy or diuretics
Your healthcare provider will talk to you about all of the health concerns and other factors that can affect your lab results, including HCT.
FAQs
What happens if HCT is low?
You may feel weak or fatigued due to reduced oxygen delivery to your tissues. Long-term low hematocrit can strain the heart and organs.[8]
How do you fix low HCT?
Treatment depends on the cause. Iron supplementation, dietary adjustments, or addressing underlying illness may be necessary. [9]
How does a low HCT make you feel?
Common symptoms include tiredness, dizziness, shortness of breath, and reduced exercise tolerance.[8]
What happens if HCT is high?
You may be at risk for blood clots, headaches, or heart problems. Hydration, altitude adjustment, or treatment for underlying disease may help.[7]
Does drinking water lower hematocrit?
Yes—rehydration can lower an artificially high HCT caused by dehydration. [10]
What diseases cause low hematocrit?
Conditions such as chronic kidney disease, leukemia, lupus, and other bone marrow disorders can lower HCT. [11]
How Everlywell Can Help
Everlywell offers at-home lab tests that can help you monitor your overall health, including red blood cell–related markers. The Everlywell 360 test provides a comprehensive overview of your health by examining 83 biomarkers. These tests are physician-reviewed and come with clear insights and next steps, so you can make informed decisions about your wellness from home.
Understanding your hematocrit level can offer important clues about your overall health and oxygen-carrying capacity. Whether your HCT is slightly outside the normal range or more significantly elevated or decreased, knowing the potential causes empowers you to take action. If you have more questions about your options for testing and what your results may mean, consider scheduling a virtual visit and talking to one of our credentialed healthcare providers.
Explore Everlywell’s suite of at-home blood tests to get the insights you need—no healthcare provider’s office or waiting room required.