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The hematocrit (HCT) test provides a key insight into your blood composition by quantifying the proportion occupied by red blood cells within your total blood volume. It determines how much of your blood comprises RBCs. These cells are vital for carrying oxygen throughout your body.
High HCT levels (usually over 44% to 50%) can indicate dehydration. Other causes of high HCT include conditions that cause your body to produce too many RBCs, such as certain lung or heart diseases. On the other hand, extremely low hematocrit results may suggest anemia or other blood disorders that affect RBC formation (erythropoiesis) or destruction (hemolysis).
Keep reading to discover the causes, symptoms, and treatments for high and low hematocrit.
Pro Tip: Hematocrit and other parts of the complete blood count (CBC) reveal essential information about your health. If you wish to learn more about what your blood test means, book a virtual consultation to speak to a healthcare provider.
If your hematocrit blood test result shows a high hematocrit, the proportion of red blood cells in your blood is higher than expected. A normal hematocrit typically falls between 41% and 50% for adult men. The normal range of hematocrit for adult women is usually between 36% and 44%. A result above these ranges is considered high.
Symptoms of high hematocrit(1) include:
A high hematocrit can indicate several underlying health conditions, such as dehydration, lung disease, or certain types of cancer. It can also indicate that blood plasma, the liquid component of blood, is too low.
One of the most frequent reasons for an elevated HCT level is dehydration(2). When dehydrated, your body loses fluids–often through sweating, vomiting, or diarrhea. This fluid loss reduces the volume of plasma. Since the number of RBCs stays the same, they become more concentrated within the smaller plasma volume. This leads to a higher hematocrit reading.
Chronic obstructive pulmonary disease (COPD) and other conditions affecting lung function can significantly impair the lungs’ ability to absorb oxygen. COPD damages the air sacs (alveoli) in the lungs, making it harder for oxygen to pass into the bloodstream.
Your body will produce more RBCs to compensate for the oxygen shortage. If you have symptoms of pulmonary disorders, your doctor may order additional laboratory tests, including lung function blood tests.
People with certain types of heart disease, such as congestive heart failure and congenital heart defects, are often prone to high hematocrit and hemoglobin levels. When the heart cannot pump blood effectively, the body may try to compensate by increasing the production of RBCs (erythrocytes).
As the heart cannot fully function to facilitate blood circulation, your body will counteract the loss with increased erythrocyte production. Thus, an HCT blood test also provides additional information about your risk for cardiovascular diseases, making it a key part of heart health blood tests.
The primary cancer type that drives your bone marrow to produce excessive RBCs is called polycythemia vera(3). Although extremely rare, this blood cancer slows down blood circulation and leads to an enlarged spleen, increased blood clotting, and other life-threatening blood-related complications. Naturally, it also elevates your normal hematocrit levels.
On the other hand, kidney cancer also influences erythrocyte production since it releases the protein (erythropoietin) that prompts the process. Additional tests, such as a red blood cell count, biopsy, MRI, etc can further confirm this.
Did You Know? Certain cancers release specific molecules called biomarkers into the bloodstream. These biomarkers can be detected through specialized blood tests, sometimes before noticeable symptoms appear. For example, the PSA test can help detect prostate cancer, while the CA-125 test is used for ovarian cancer.
In some cases, these cancers are first spotted through routine exams. Learn more about the types of cancer diagnosed through blood testing.
Lowering your high HCT will depend on its cause. For example, if it’s due to dehydration, your doctor might recommend increasing your fluid intake, using oral rehydration solutions (like those used for athletes or to treat diarrhea), or, in severe cases, receiving intravenous fluids.
If your test result goes significantly above the normal range for HCT, phlebotomy may be necessary(4). This involves removing a small amount of blood from your body, similar to donating blood, to reduce the concentration of red blood cells.
It’s important to remember that these treatments address the high HCT levels, but it’s also essential to diagnose and treat the underlying condition causing the elevated red blood cell count. Depending on the specific cause, this might involve medications, lifestyle changes, or other therapies.
While high HCT can be a concern, low HCT levels also indicate potential health issues.
If your hematocrit test result is lower than normal (typically less than 41% for men and 36% for women), it indicates that your body may be producing fewer red blood cells or destroying them at a faster rate. This could be potentially due to an underlying illness.
The most common cause of low hematocrit is anemia, characterized by a reduced number of healthy RBCs. You may spot anemia through the following symptoms:
The following are some common culprits behind a low HCT, ranging from nutritional deficiencies and blood loss to underlying medical conditions. Understanding these causes is crucial for proper diagnosis and treatment, paving the way to restoring your red blood cell levels and overall health.
As mentioned above, low HCT often points to anemia, a condition where your body doesn’t have enough healthy RBCs to carry adequate oxygen to your tissues. There are many different types of anemia, each with varying causes:
Identifying the specific type of anemia allows your doctor to recommend the most appropriate treatment to address the underlying cause. Essentially, this will help restore your red blood cell count to a healthy level.
Those who suffer from bacterial ulcers caused by H. pylori may have decreased HCT in their blood test. H. pylori infection can lead to the formation of sores in the stomach lining, causing irritation and inflammation that may result in bleeding. This chronic blood loss, even if small, can gradually deplete the body’s red blood cell count, leading to lower HCT levels.
Did You Know? It’s possible to experience blood loss without seeing blood in your stool, as the naked eye does not easily detect it. Get the fecal occult blood test to determine if you have chronic digestive bleeding.
While their primary role is filtering waste products from the blood, your kidneys also have a crucial hand in producing RBCs. This is done through a hormone called erythropoietin (EPO)(5), which acts like a messenger signal. EPO travels from the kidneys to the bone marrow, where it stimulates the production of RBCs.
When your kidneys are damaged, such as in chronic kidney disease (CKD), they can’t produce enough EPO. This shortage leads to a decrease in RBC production.
Chronic inflammatory conditions, such as lupus and rheumatoid arthritis, can significantly impact red blood cell production. This is because inflammation disrupts the intricate process of RBC formation and maturation in several ways:
Similarly, inflammatory bowel disease (IBD)(6) can contribute to anemia and low hematocrit by impairing the absorption of essential nutrients in the digestive tract. These nutrients, including iron, copper, vitamin B12, and folate, are crucial for the production of RBCs.
Leukemia and lymphoma are types of blood cancer that disrupt the normal function of bone marrow, the spongy tissue inside your bones where blood cells are produced. This disruption can significantly impact your hematocrit (HCT) levels.
Diagnosing and treating these complex conditions that lower HCT requires a comprehensive approach. Your healthcare provider will carefully evaluate your medical history, conduct a thorough physical examination, and analyze the results of various tests to arrive at an accurate diagnosis.
Once the underlying cause is identified, your doctor will create a tailored treatment plan to address the specific condition and ultimately restore your HCT to a healthy range. This might involve medications, transfusions, or other therapies depending on the nature of the disorder.
If low HCT is due to iron-deficiency anemia, your doctor may recommend supplements and certain lifestyle adjustments. Learn more about iron deficiency anemia and its physical impact, especially among women.
On the other hand, if the condition is linked to more complex disorders like cancer, blood disease, CKD, etc., your healthcare provider will need more information to form an accurate diagnosis, entailing other types of assessment. Only then will your doctor prescribe a treatment that covers the process of bringing HCT back to its normal range.
Calculating hematocrit involves measuring the ratio of red blood cells through a reading device. One traditional method involves using a capillary tube, a thin glass tube, to collect a small amount of blood. This tube is then spun in a centrifuge, a machine that spins rapidly, separating the blood components based on their density. Since red blood cells are the densest component of blood, they settle to the bottom of the tube when a blood sample is spun in a centrifuge.
After centrifugation, the tube displays distinct layers: a packed column of RBCs at the bottom, a thin layer of white blood cells and platelets (the “buffy coat(7)“) in the middle, and plasma, the liquid portion of blood, at the top.
To calculate the hematocrit, a special reading device is used to measure the length of the packed red blood cell column and compare it to the total length of the blood sample in the tube. This ratio, expressed as a percentage, represents the hematocrit value.
The timing of this analysis is critical. Ideally, the hematocrit should be measured within 10 minutes of collecting the blood sample. This urgency stems from the fact that over time, the neatly separated layers within the capillary tube can start to mix.
Your doctor will likely order a hematocrit blood test if you exhibit symptoms of anemia, blood loss, dehydration, and other blood disorders. As part of the CBC test, it also provides critical information on other disorders, such as cancer, lung disease, kidney disease, and cardiovascular diseases.
Unlike the other tests involved in CBC, an HCT blood test will require a venous blood sample. This is drawn from the veins at the back of your elbow and should only be performed by a licensed phlebotomist. HCT measurement needs more blood volume for accurate processing and analysis.
An HCT blood test alone does not require fasting or other special preparations prior to blood collection. But if it is part of a more extensive test or you’re taking another test simultaneously, you may have to abstain from consuming food, drinks, and certain medications.
Pro Tip: Venipuncture, the process of inserting a syringe needle into your vein to collect blood, can be slightly uncomfortable. If you are anxious about your lab test appointment, read our tips on calming yourself before getting blood drawn.
Healthy hematocrit levels typically fall between 41% and 50% for men and 36% and 44% for women. HCT test values above or below these ranges signal problems in the blood, ranging from anemia to blood loss for low HCT percentage and dehydration to blood cancer for high lab values. Either way, see your doctor for a proper diagnosis and additional lab tests.
Elevated hematocrit (HCT) can lead to persistent fatigue because the increased concentration of red blood cells thickens the blood, making it harder for the heart to pump and slowing the delivery of oxygen throughout the body. This reduced blood flow can leave you feeling tired and sluggish, as your organs and tissues, including the brain, receive less oxygen than they need to function optimally.
A low hematocrit (HCT) can indicate conditions like anemia, where there are fewer red blood cells, or certain blood disorders that affect red blood cell production. Conversely, a high HCT often suggests dehydration, as a reduced fluid volume in the body leads to a higher concentration of RBCs. This is because the same number of RBCs occupy a smaller proportion of the total blood volume when plasma levels are low.
Did You Know? Aside from an HCT blood test, other ways to detect dehydration include a urinalysis and the electrolyte blood test panel. Severe dehydration treatment includes IV fluids and oral rehydration solution (ORS).
An HCT blood test is a valuable tool for detecting a range of health conditions, particularly those affecting red blood cell production, such as anemia or polycythemia. However, HCT results alone are not a definitive diagnosis and require careful interpretation by a healthcare professional. Misinterpreting these results can lead to unnecessary anxiety or a false sense of security, highlighting the importance of discussing them with your doctor, either during an in-person or virtual consultation.
1 Mondal H, Zubair M. Hematocrit. [Updated 2024 Oct 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542276/
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