Blood Smear

Test Description

There are many quantitative blood tests available to the health-care provider that provide
an enormous amount of information about the various blood components. However, the
blood smear, a qualitative measure, is viewed as being equally, if not more, informative.
The test involves the preparation of a smear of peripheral blood on a slide. The
smear is then microscopically examined to note the appearance of the red blood
cells, white blood cells, and platelets. Red blood cells are examined in terms of
size, shape, color, and structure. Examination of the white blood cells provides data
regarding total quantity and differential count (see “White Blood Cell Count and
Differential”). Platelets are also examined for number and the presence of abnormal
appearance, or thrombocytopathy.
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Normal Values

Normal quantity and appearance of red blood cells, white blood cells, and platelets
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Possible Meanings of Abnormal Values

White Blood Cells: See White Blood Cell Count and Differential
Platelets: See Platelet Count
Red Blood Cell Abnormalities:
Abnormal colors
Hyperchromic (highly colored due to concentrated hemoglobin) as seen in dehydration
Hypochromic (pale cells due to low hemoglobin content) as seen in anemia

Abnormal sizes

Anisocytes (vary in size): Seen in anemia
Macrocytes (large): Seen in macrocytic anemias such as pernicious anemia and folic
acid deficiency, increased erythropoiesis, and postsplenectomy anemia
Microcytes (small): Seen in microcytic anemias such as iron deficiency and thalassemia
major

Abnormal shapes
Ovalocytes/elliptocytes (oval or elliptical shaped cells): Seen in microcytic anemias
(iron deficiency, thalassemia), megaloblastic anemia and hemoglobinopathies
Poikilocytes (irregular in shape): Seen in anemia
Schistocytes (fragmented cells noted for their unusual shapes [helmet, spirals, triangles]):
Seen in hemolytic anemia, prosthetic heart valves, severe valvular heart disease,
and severe burns
Sickle cells (crescent-shaped due to abnormal hemoglobin [Hb S]): Seen in sickle cell
anemia
Spherocytes (small and round cells, instead of normal biconcave shape): Seen in hereditary
spherocytosis and immunohemolytic anemia
Target cells (thin cells, with less hemoglobin present): Seen in hemoglobin C disease/
trait, thalassemia minor, iron deficiency anemia, liver disease, and postsplenectomy

Other RBC abnormalities

Basophilic stippling (dark spots caused by abnormal hemoglobin synthesis): Seen in
thalassemia and lead or heavy-metal poisoning
Heinz-Ehrlich bodies (particles of denatured hemoglobin attached to the cell membrane):
Seen in congenital glucose-6-phosphate dehydrogenase deficiency, druginduced
hemolytic anemias, and unstable hemoglobin disorders after splenectomy
Howell-Jolly bodies (dark purple spherical bodies [remnants of nuclear material]):
Occasionally seen in severe hemolytic anemias, pernicious anemia, leukemia, thalassemia,
myelodysplasias, and in postsplenectomy
Rouleaux formation (RBCs stick to one another): Seen in cryoglobulinemia, giant cell
arteritis, macroglobulinemia, and multiple myeloma
Stomatocytes (one or more slitlike areas of central pallor are present, producing a mouthlike
appearance): Seen in acute alcoholism, congenital stomatocytosis, with drugs such
as phenothiazines, and with neoplastic, cardiovascular, and hepatobiliary diseases
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Contributing Factors to Abnormal Values
• The quality of the microscopic examination is highly dependent on the knowledge
and experience of the individual performing the examination.
• Hemolysis of specimen may alter test results.

Interventions/Implications

Pretest
• Explain to the patient the purpose of the test and the need for a blood sample to be drawn.
• No fasting is required before the test.
Procedure
• The blood smear may be prepared from blood obtained from a finger or heel stick (in
  infant) or from venipuncture.
• If a venipuncture is used, blood is drawn in a lavender-top collection tube containing
  EDTA.
• Gloves are worn throughout the procedure.
Posttest
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Report abnormal findings to the primary care provider.

Clinical Alerts            

• If blood smear is found to be abnormal, follow-up testing via bone marrow aspiration
or biopsy may be done.