Taking blood for the test is quick and simple. The nurse or medical professional will use a small needle to draw the blood from the arm. A person is likely to feel a slight scratching or stinging sensation when the needle breaks the skin. The blood sample will flow from the needle into a tube.
Once the tube is full, the medical professional will remove the needle. They will often instruct the person to hold a piece of gauze against the site to stop any bleeding, before applying a bandage.
The blood sample is then sent to a lab, where a technician will check for red cell size and distribution. RDW results describe the variation in size and volume of red blood cells in a sample. Results may be normal or high, and the ranges are nuanced. A result in the normal range for an adult female will be A person with a normal result may still have an underlying condition.
An MCV test measures the average volume of a red blood cell. Results may show:. In , researchers concluded that a high RDW result might be linked to poor outcomes in people with heart failure , or further cardiovascular events in people who have experienced a heart attack. Anemia can be treated with medications, dietary changes, and supplements. However, untreated anemia can lead to severe complications. In some cases, it can be fatal.
Results can indicate the presence of anemia and help to pinpoint the underlying cause. Microcytic anemia occurs when the body does not get enough oxygen and cannot provide enough energy to all organs and tissues, causing pale skin and…. If your health care provider has also ordered other blood tests, 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 a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. RDW results help your health care provider understand how much your red blood cells vary in size and volume.
Even if your RDW results are normal, you may still have a medical condition needing treatment. That's why RDW results are usually combined with other blood measurements. This combination of results can provide a more complete picture of the health of your red blood cells and can help diagnose a variety of conditions, including:. Learn more about laboratory tests, reference ranges, and understanding results.
If your test results indicate you have a chronic blood disorder, such as anemia, you may be put on a treatment plan to increase the amount of oxygen that your red blood cells can carry.
Be sure to talk to your doctor before taking any supplements or making any changes in your eating plan. 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. What is a red cell distribution width test? What is it used for? The RDW test may also be used to diagnose: Other blood disorders such as thalassemia , an inherited disease that can cause severe anemia Medical conditions such as heart disease , diabetes , liver disease , and cancer , especially colorectal cancer. Use precise geolocation data. Select personalised content. Create a personalised content profile.
Measure ad performance. Select basic ads. Create a personalised ads profile. Select personalised ads. Apply market research to generate audience insights. Measure content performance. Develop and improve products. List of Partners vendors. Red cell distribution width RDW is one of the numbers or blood cell indices that is included as part of a complete blood count CBC , and describes the variation in the size of red blood cells in a sample of blood.
A higher RDW means that there is a greater variation in the size of red blood cells than expected. The RDW can be very helpful in distinguishing between the different types of anemia , especially if there is more than one type of anemia present.
Even when blood counts such as the red blood cell count are normal, however, the RDW can be a valuable test. For example, it can predict iron deficiency in pregnant women even before anemia occurs iron deficiency increases the risk for both mothers and babies. It may also be helpful in estimating heart disease or cancer risk, and some healthcare providers believe, may be a test that assesses overall well-being.
There are limitations in evaluating the RDW such as after a person has had a blood transfusion. The red cell distribution width RDW is done as part of a CBC and is, therefore, a commonly performed test that is used both for screening healthy individuals and to evaluate a wide range of medical conditions.
There are times when healthcare providers may specifically look at the value of RDW:. The RDW is used to describe the amount of variation in the size of red blood cells, with the term anisocytosis used to describe this variation. In other words, talking about significant anisocytosis on a blood smear would mean that the red blood cells vary significantly in size.
Red blood cells are usually fairly uniform in size, and an increase in variation or anisocytosis an increased RDW can mean several things. A high RDW can be a sign of some types of anemia as well as a general sign of inflammation in the body.
If a lab uses EDTA anticoagulated blood instead of citrated blood, the reading will be falsely high. Variation in red blood cell size may also be noted visually by looking at a peripheral smear for morphology, though this test is usually done after a CBC to investigate an abnormality.
Since the RDW is done as part of a CBC, the number is reported along with several other values and the combination of results is usually used rather than the RDW alone. These include the number of each type of the blood cells and other red blood cell indices. In addition to the CBC, other tests that may be ordered to evaluate anemia include a reticulocyte count , blood smear for morphology, iron studies, and more.
Since the RDW is part of a simple blood test, there are very few risks. Uncommonly people may experience bleeding at the puncture site, bruising a hematoma , or infection. You will need to have your insurance card and it's helpful to provide your healthcare provider with any previous CBC results for comparison.
A CBC may be drawn in the hospital as well as many clinics. Before drawing your blood, a lab technician will clean the area usually an arm with antiseptic and apply a tourniquet to make the vein easier to see. She will then insert the needle through your skin and into the vein. While the needle is inserted you may feel a sharp but short sting, and some people may experience lightheadedness or feel faint.
After the sample is removed, the needle is removed and pressure applied to the puncture wound. A dressing is then applied to keep the area clean and reduce any bleeding.
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