The original method for hematocrit measurement is the macrohematocrit Wintrobe hematocrit tube method. It uses a narrow glass tube and a centrifuge machine. The centrifuge separates the blood into three main layers: red blood cells, white blood cells, and platelets, in that order from the bottom up. The macrohematocrit method carries the risk of measuring trapped plasma as part of the red blood cell layer, which erroneously elevates the hematocrit percentage. A newer method is the microhematocrit method, which uses a capillary tube instead of a narrow glass tube and requires a smaller quantity of blood and less time.
The microhematocrit method traps less plasma because the diameter of the capillary tube is smaller than the Wintrobe hematocrit tube. So the percentage of hematocrit is more accurate in the microhematocrit method than in the macrohematocrit method. Both procedures require the technician to manually measure the length of the layers.
The technician calculates hematocrit as the length of the packed red blood cell layer divided by the length of total cells and plasma. This ratio is then multiplied by to give a certain percentage. Today, these two methods have been largely succeeded by an automated hematology analyzer where the hematocrit test is obtained as part of a complete blood count CBC laboratory test.
The hematocrit is calculated indirectly from the average volume and the number of red blood cells. However, automated analyzers may not be available in areas where resources are low. In the microhematocrit method, a technician only needs a small sample of blood from a finger-prick. In the other methods, the technician draws blood from the inner side of your arm or the back of your hand. Before drawing blood for the measurement, the technician first cleans the surface from where your blood would be drawn.
An HCT test is usually ordered as part of a complete blood count CBC in which multiple tests are run from blood taken at one time, so you may need to have more than one vial of blood drawn. In addition to the full CBC, other tests may be performed at the same time or as a follow-up to help with a diagnosis, including:. The centrifuge separates the erythrocytes red blood cells from the white blood cells and platelets, giving a direct measure of the percentage of RBCs in the blood sample.
The automated instrument, which calculates the average RBC volume rather than a direct measurement, provides quick results, but can produce false positive results. Depending on the purpose of the test, your healthcare provider will determine which method is best.
If your levels are below or above normal, you could be at risk for one of these serious health conditions. Elevated testosterone levels. HCT test results may be affected by other factors such as a recent blood transfusion, pregnancy, or living at a high altitude. Your healthcare provider should review with you the results of the HCT and all other tests that were done. If the results indicate that you're anemic, you can take some simple steps to improve your red blood cell count by fortifying your diet or using over-the-counter iron supplements.
If anemia is the result of an infection, you may need to begin antibiotics. When test results point to a bone marrow problem, a bone marrow examination may be needed in which a sample of bone marrow is taken, usually from the hip, to check for lymphoma and similar disorders. Conditions related to an overproduction of RBCs may require lifestyle changes such as quitting smoking or adopting a heart-healthy diet. In the rare case of PV, healthcare providers can provide medication that will help you manage the condition, but it cannot be cured.
Anytime your levels are outside the normal hematocrit range, your healthcare provider will likely repeat the HCT test at least annually to check on your condition. No one likes to get pricked with a needle. However, an HCT test is one of those "worth the pain" tests. It's quick and easy and goes a long way in helping healthcare providers get a more complete picture of your overall health.
The source of everyday problems such as fatigue or headaches might be revealed as simple anemia or a more serious blood disorder that needs immediate care. In either instance, one simple blood draw can make a huge difference. Sign up for our Health Tip of the Day newsletter, and receive daily tips that will help you live your healthiest life. National Heart, Lung, and Blood Institute.
Polycythemia Vera. American Cancer Society. Understanding Your Lab Test Results. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
You don't need any special preparations for a hematocrit test. If your health care provider has ordered more tests on your blood sample, you may need to fast not eat or drink for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.
There is very little risk to having a hematocrit test or other type of blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. If your results are not in the normal range, it doesn't necessarily mean that you have a medical condition requiring treatment. To learn more about your results, talk to your health care provider.
Learn more about laboratory tests, reference ranges, and understanding results. Many factors can affect your hematocrit levels, including a recent blood transfusion, pregnancy , or living at a high altitude. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. Hematocrit Test. What is a hematocrit test?
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