| Definition: |
A blood test that provides information about the number and shape of blood cells by visual inspection.
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| Alternative Names: |
Blood smear
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child (may also be used for adults):
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
The blood is examined under a microscope. It may be examined by a special automated "calculator", a technologist, a hematologist, and/or a pathologist. Information is obtained about the relative number and kinds of white blood cells (differential), morphological (shape) abnormalities of all types of blood cells, and a rough estimate of white cell and platelet counts. |
| How to prepare for the test: |
Adults:
No special preparation is necessary.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
| This test may be performed as part of a general health examination, to help in the diagnosis of many illnesses, or when an abnormality of any type of blood cell is suspected. |
| What abnormal results mean: |
Red cell abnormalities such as anisocytosis (size), poikilocytosis (shape), hypochromia (lack of color), polychromatophilia (multiple colors), rouleaux (nonspecific coating by serum globulins) are determined. Some abnormalities may be graded on a 4 point scale:
1+: 25%
2+: 50%
3+: 75%
4+: 100% of cells affected
The presence of target cells may indicate:
The presence of spherocytes may indicate:
The presence of elliptocytes may indicate:
- hereditary elliptocytosis
The presence of schistocytes may indicate:
The presence of normoblasts may indicate:
The presence of burr cells (echinocytes) may indicate:
- artifact (induced result) from specimen preparation
- uremia
The presence of spur cells (acanthocytes) may indicate:
The presence of teardrop cells may indicate:
- myelofibrosis
- leukoerythroblastic anemia
- thalassemia major
- severe iron deficiency
The presence of Howell-Jolly bodies may indicate:
The presence of Heinz bodies (with crystal violet stain) may indicate:
- G6PD deficiency
- congenital hemolytic anemia
- unstable hemoglobin variant (unstable form of hemoglobin)
- alpha thalassemia
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:
Additional conditions under which the test may be performed:
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| What the risks are: |
- excessive bleeding
- fainting or feeling light-headed
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
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| Special considerations: |
| The accuracy of this test depends, in part, on the experience of the person examining the sample. Experienced cell examiners can determine significant amounts of information from the peripheral smear. |
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