Blood smear

• Illustrations
• Alternative names
• Definition
• How the test is performed
• How to prepare for the test
• How the test will feel

• Why the test is performed
• Normal Values
• What abnormal results mean
• What the risks are
• Special considerations

Alternative names    Return to top

Definition    Return to top

This blood test provides information about the number and shape of blood cells by visual inspection.

How the test is performed    Return to top

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, and 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 circulation. Once the blood has been collected, the needle is removed, and 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 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 an automated "calculator," a technologist, a hematologist, or a pathologist. The smear shows the relative number and kinds of white blood cells (differential), abnormalities in the shape of all types of blood cells, and a rough estimate of white cell and platelet counts.

How to prepare for the test    Return to top

No special preparation is necessary.

For infants and children, the preparation you can provide for this test depends on your child's age and previous experience. For general information regarding how you can prepare your child, see the following topics:

• Infant test or procedure preparation (birth to 1 year)
• Toddler test or procedure preparation (1 to 3 years)
• Preschooler test or procedure preparation (3 to 6 years)
• Schoolage test or procedure preparation (6 to 12 years)
• Adolescent test or procedure preparation (12 to 18 years)

How the test will feel    Return to top

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    Return to top

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.

Normal Values    Return to top

• Normal differential
• Normal appearance of cells

What abnormal results mean    Return to top

Red cell abnormalities such as size, 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:

• Decreased osmotic fragility
• Liver disease (especially obstructive jaundice)
• Hemoglobinopathies (hemoglobin abnormalities)
• Thalassemia
• Post-splenectomy
• Deficiency in an enzyme called lecithin cholesterol acyl transferase
• Deficiency in iron

• Increased osmotic fragility
• Hereditary spherocytosis
• Immunohemolytic anemia

The presence of elliptocytes may indicate hereditary elliptocytosis.

The presence of schistocytes may indicate:

• Microangiopathic hemolytic anemia
• Disseminated intravascular coagulation (may be due to gram-negative sepsis or malignancy)
• Thrombotic thrombocytopenic purpura (TTP)
• Aortic valve prosthesis (artificial heart valve)
• Hemolytic uremic syndrome (HUS)

• Severe hemolysis
• Leukoerythroblastic anemia (myelophthisis process)
• Myelofibrosis
• Cancer that has spread to bone marrow
• Thalassemia
• Post-splenectomy
• Miliary tuberculosis
• Erythroblastosis fetalis

• Artifact (induced result) from specimen preparation
• Uremia

• Severe liver disease
• Abetalipoproteinemia

• Myelofibrosis
• Leukoerythroblastic anemia
• Thalassemia major
• Severe iron deficiency

• Post-splenectomy
• Sickle cell anemia
• Myelodysplasia

• 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:

• 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

What the risks are    Return to top

The risks associated with having blood drawn are minimal:

• 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

Special considerations    Return to top

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 blood smear.