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Lifespan’s A - Z Health Information Library |
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Blood smearDefinitionA blood smear is a blood test that gives information about the number and shape of blood cells. Alternative NamesPeripheral smear How the Test is PerformedBlood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood. Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding. The blood sample is sent to a lab, where the health care professional looks at the it under a microscope. Or, the blood may be examined by an automated machine. The smear shows the number and kinds of white blood cells (differential), abnormally shaped blood cells, and gives a rough estimate of white cell and platelet counts. How to Prepare for the TestNo special preparation is necessary. How the Test Will FeelWhen the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing. Why the Test is PerformedThis test may be performed as part of a general health exam to help diagnose many illnesses. Or, your doctor may order this test if you have signs of a blood disorder. Additional conditions under which the test may be performed:
Normal ResultsRed cells normally are the same in size and color and have a lighter-colored area in the center. The blood smear is considered normal if there is:
What Abnormal Results MeanAbnormal results mean there is an abnormalities in the size, shape, coloring or coating of the red blood cells. Some abnormalities may be graded on a 4-point scale:
The presence of target cells may be due to:
The presence of elliptocytes may be a sign of hereditary elliptocytosis. The presence of fragmented cells (schistocytes) may be due to:
The presence of a type of immature red blood cell called a normoblast may be due to:
The presence of reticulocytes (more than 2% of total red cells; seen with special stain) may indicate hemolytic anemia or hemorrhage. The presence of basophilic stippling may indicate:
The presence of sickle cells may indicate sickle cell anemia. RisksThe risks associated with having blood drawn are minimal:
ConsiderationsThe accuracy of this test depends, in part, on the experience of the person looking at the sample. Experienced cell examiners can get a lot of information from the blood smear. ReferencesNewland J. The peripheral blood smear. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 161. Review Date: 2/13/2009
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. The information provided herein should not be used during any
medical emergency or for the diagnosis or treatment of any medical
condition. A licensed medical professional should be consulted for
diagnosis and treatment of any and all medical conditions. Call 911
for all medical emergencies. Links to other sites are provided for
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other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the
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