Definition
A blood smear is a blood test that gives information about the number and shape of blood cells.
Alternative Names
Peripheral smear
Why the Blood smear is Performed
This test may be performed as part of a general health exam, to help diagnose many illnesses. Or it may be done when the health care provider suspects an abnormality of any type of blood cell.
How the Blood smear is Performed
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.
A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore normal blood flow. Once the blood has been collected, the needle is removed. The puncture site is covered to stop any bleeding.
For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a small glass tube (pipette), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if bleeding continues.
A technologist, blood specialist (hematologist), or disease specialist (pathologist) looks at the blood under a microscope. Or, the blood may be examined by an automated "calculator." 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 Blood smear
No special preparation is necessary.
How the Blood smear Will Feel
When 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.
Risks
The risks associated with having blood drawn are minimal:
- Excessive bleeding
- Fainting or feeling light-headed
- Blood collecting under the skin (hematoma)
- Infection
- Many needle sticks to find veins
Considerations
The 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.
Normal Results
- Normal differential
- Normal appearance of cells
What Abnormal Results Mean
Red cell abnormalities such as size, shape, lack of color (hypochromia), many colors (polychromatophilia), and coating by blood proteins called serum globulins (rouleaux) are determined. Some abnormalities may be graded on a 4-point scale:
- 1+: 25% of cells affected
- 2+: 50% of cells affected
- 3+: 75% of cells affected
- 4+: 100% of cells affected
The presence of target cells may indicate:
- Decreased osmotic fragility
- Liver disease (especially obstructive jaundice)
- Hemoglobin abnormalities (hemoglobinopathies)
- Thalassemia
- Post-splenectomy
- Deficiency in an enzyme called lecithin cholesterol acyl transferase
- Deficiency in iron
The presence of spherocytes may indicate:
- Increased osmotic fragility
- Hereditary spherocytosis
- Autoimmune hemolytic anemia
The presence of elliptocytes may indicate hereditary elliptocytosis.
The presence of schistocytes may indicate:
- Microangiopathic hemolytic anemia
- Disseminated intravascular coagulation
- Thrombotic thrombocytopenic purpura (TTP)
- Artificial heart valve (aortic valve prosthesis)
- Hemolytic uremic syndrome (HUS)
The presence of normoblasts may indicate:
- Severe hemolysis
- Leukoerythroblastic anemia (myelophthisis process)
- Myelofibrosis
- Cancer that has spread to bone marrow
- Thalassemia
- Post-splenectomy
- Miliary tuberculosis
- Erythroblastosis fetalis
The presence of burr cells (echinocytes) may indicate:
- Artifact (induced result) from specimen preparation
- Uremia
The presence of spur cells (acanthocytes) may indicate:
- Severe liver disease
- Abetalipoproteinemia
The presence of teardrop cells may indicate:
- Myelofibrosis
- Leukoerythroblastic anemia
- Thalassemia major
- Severe iron deficiency
The presence of Howell-Jolly bodies may indicate:
- Post-splenectomy
- Sickle cell anemia
- Myelodysplasia
The presence of Heinz bodies (with crystal violet stain) may indicate:
- G6PD deficiency
- Congenital hemolytic anemia
- Unstable form of hemoglobin (unstable hemoglobin variant)
- 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:
- Myelofibrosis
- Myelophthisic process
- Lead poisoning
The presence of sickle cells may indicate sickle cell anemia.
Additional conditions under which the test may be performed:
- Clinical hemoglobin C
- Hairy cell leukemia
- Non-Hodgkin's lymphoma
- Any known or suspected blood disorder
- Monitoring the side effects of chemotherapy
