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Hematocrit (HCT) Blood Test: What It Means to Get High or Low Results

Table of Contents

blood collection from a patient passing tests

The hematocrit or HCT blood test measures the proportion of red blood cells to white blood cells, platelets, and plasma. 

High HCT blood test values (usually over 44% to 50%) indicate dehydration and conditions that cause RBC overproduction. Alternatively, extremely low hematocrit results may indicate anemia or other blood disorders that affect RBC formation (erythropoiesis) or destruction (hemolysis). 

Know more about the concerning levels of HCT and what the test results tell you when you read on.

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. 

High HCT Meaning 

If your HCT blood test result shows high hematocrit, over 50% for men and 44% for women, it suggests that you have more red blood cells or erythrocytes due to an underlying health condition. It could also indicate that blood plasma is in critically low volume. 

Symptoms of high hematocrit include:

  • Fatigue
  • Dizziness 
  • Headaches
  • Vision problems
  • Skin blushing or flushing

Causes of High HCT

Dehydration

If you have high HCT, you are likely to be dehydrated. In this case, you may not necessarily be producing too many RBCs. Instead, your blood has a low volume of plasma which stems from a lack of proper hydration. 

Lung Disease

Conditions affecting lung function, such as chronic obstructive pulmonary disease (COPD), can affect the organ’s ability to obtain oxygen. To compensate for the oxygen shortage, your body will produce more RBCs. If you have symptoms of pulmonary disorders, your doctor may order additional laboratory tests, including lung function blood tests

Heart Disease

People with heart disease are prone to high hematocrit and hemoglobin. As the heart cannot function fully to facilitate blood circulation, your body will counteract the said 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

Cancer

The primary cancer type that drives your bone marrow to produce excessive red blood cells is called polycythemia vera. 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. This can be further confirmed by additional tests, such as a red blood cell count, biopsy, MRI, etc. 

Did You Know? Several cancers can be detected by biomarkers screened through a blood test. In some cases, these cancers are first spotted through routine exams. Learn more about the types of cancer diagnosed through blood testing

Treatment for Elevated HCT

Lowering your high HCT will depend on its cause. For example, if it’s due to dehydration, your healthcare provider may recommend rehydration therapy. If your test result goes extremely above the normal range for HCT, your doctor may push for phlebotomy, wherein blood is extracted to reduce red blood cell count. 

Low HCT Meaning 

To get an HCT below the normal hematocrit range (less than 41% for men and 36% for women) indicates low red blood production or a high rate of destruction, potentially due to an underlying illness. 

The most common cause of low hematocrit is anemia, characterized by a reduced number of healthy red blood cells. You may spot anemia through the following symptoms:

  • Fatigue
  • Dizziness 
  • Chest pain
  • Headaches 
  • Pale complexion
  • Trouble breathing
  • Cold hands and feet
  • Irregular heartbeat (arrhythmia) 

Causes of Low HCT

Anemias 

As mentioned above, low HCT typically signals anemia, which can be due to a lack of nutrients, such as that in iron-deficiency anemia, or genetic factors like what’s causing sickle cell anemia and aplastic anemia. Additional blood tests are needed to verify the condition, including the anemia profile blood test

Blood Loss

Women who experience excessive menstrual bleeding are likely to have low HCT. In the same way, those who suffer from bacterial ulcers caused by H. pylori and other similar disorders leading to internal bleeding can also expect decreased HCT in their blood test. 

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.

Thalassemia 

Thalassemia is an inherited blood disorder wherein your body fails to produce enough hemoglobin, a crucial protein in the red blood cell. As a result, RBCs are low, indicated by low HCT and erythrocyte count.  

Kidney Problems

Your kidneys don’t just filter wastes from the blood. They also produce the protein erythropoietin, which signals the production of RBCs. Hence, disorders like chronic kidney disease (CKD) and other significant kidney problems lead to low secretion of erythropoietin, resulting in inadequate RBCs. 

Inflammatory Diseases

Conditions like lupus and rheumatoid arthritis, characterized by increased inflammatory activities, negatively influence RBC formation and maturation. Similarly, inflammatory bowel disease (IBD) may also promote anemia leading to low HCT as it affects the absorption of iron, copper, vitamin B12, and other fundamental nutrients for erythropoiesis.  

Cancers

Leukemia and lymphoma are two types of cancers that directly impact bone marrow function. Hence, with these underlying conditions, you may likely get low HCT in your blood test and undergo further testing. 

Treatment for Low HCT

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 in which HCT is brought to its normal range.

How Is Hematocrit Measured?

Calculating hematocrit involves measuring the ratio of red blood cells through a reading device. When using a capillary tube, the length of the RBC packed length volume is compared to the total length of the blood sample. 

It is imperative to have the analysis within 10 minutes of the sample collection, as the erythrocyte layers can mix with the other blood components and platelets begin to clot. 

How and When Is It Done?

Your doctor will likely order an HCT 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, liver problems, and cardiovascular diseases. 

Unlike the other tests involved in CBC, wherein the blood samples can be collected through finger pricking, 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 volume of blood for accurate processing and analysis. 

Additionally, 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 if 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 for blood collection, can be a little discomforting. If you are anxious about your lab test appointment, read our tips on how to calm yourself when getting blood drawn

Frequently Asked Questions

What level of HCT is concerning?

The normal hematocrit range for men is 41% to 50%, while women should have 36% to 44%. HCT test values that go 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. 

Can high HCT cause fatigue?

Feeling exhausted all the time is part of the symptoms of high HCT. The increased volume of RBCs causes the blood to be thicker and move slower, affecting the rate of oxygen distribution to cells. As a result, your brain receives less oxygen, making you tired and sleepy. 

Does low HCT mean dehydration?

It’s the other way around. Low HCT suggests conditions like anemia and other blood disorders, but it’s high HCT that indicates dehydration. The lack of sufficient fluid in your body results in blood plasma having less volume, which increases the percentage of RBC. 

Did You Know? Aside from an HCT blood test, other ways to detect dehydration include a urinalysis and the electrolyte blood test panel. Treatment for severe dehydration includes administering IV fluids and oral rehydration solution (ORS). 

The Bottom Line 

An HCT blood test helps detect various health conditions, especially blood disorders. However, without fully understanding what your test results mean may lead to misconceptions about the severity of the abnormality. In addition, it’s important to understand that a hematocrit blood test alone will not suffice as far as diagnosis goes. It’s always the best course of action to speak to your doctor whether by setting up an appointment, either for a physical or virtual consultation.

Medically Approved By Dr. Edward Salko, MD

Dr. Edward Salko is the board-certified physician who reviews lab tests provided by PERSONALABS™. He earned his Bachelor of Science in chemistry and pre-med from the University of Florida in Gainesville and his Doctor of Osteopathy Medicine in 1980 from Kansas City University School of Medicine.

Dr. Salko’s career has specialized in family and emergency medicine. His passion is to provide clients with the tools they need in the most convenient way possible to allow them to take charge of their own healthcare. He has held a variety of positions in Kansas, Florida and Washington. Currently, in addition to his duties as Medical Director for Personalabs, he is a practicing emergency physician in Kennewick, Washington.

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