Laboratory 1.2 - Blood Smear

Blood smear

A laboratory technique used to examine the characteristics of blood cells under a microscope; involves spreading a thin layer of blood onto a slide, staining it, and examining number, size, shape, and abnormalities of blood cells; crucial in diagnosing anemia, leukemia, malaria, and other infections

Anisocytosis

Variation in the size of RBCs, revealed on a blood smear

Poikilocytosis

Variation in the shape of RBCs, revealed on a blood smear

Hypochromia (blood smear)

Variation in RBC color indicating iron deficiency

Hyperchromia (blood smear)

Variation in RBC color seen in spherocytosis

Blood smear preparation

A small drop of blood is placed near one end of a clean slide; another slide is held at a 30-45° angle, touching the blood drop, and quickly slid along the length of the flat slide to create a thin smear; the smear is then allowed to air dry completely (avoiding blowing on it to prevent contamination)

Wright's stain

The staining solution applied to a blood smear for 2-4 minutes, followed by buffer for about 6 minutes, then rinsed gently with distilled water and air dried

Erythrocytes (Lab 1.2 Table 2)

4-6 million cells/mm³; transport oxygen attached to hemoglobin and trace amounts of carbon dioxide; light red, biconcave, no nucleus or organelles; lifespan of 120 days

Platelets (Lab 1.2 Table 2)

150,000-400,000 cells/mm³; initiate the clotting cascade; tiny cell fragments that stain dark purple; lifespan of 8-10 days

Leukocytes (Lab 1.2 Table 2)

4,800-10,800 cells/mm³; carry out immune response; divided into granulocytes and agranulocytes; lifespan varies from hours to years

Neutrophils (Lab 1.2 Table 2)

3,000-7,000 cells/mm³ (40-70% of WBCs); phagocytosis increases during acute infections; staining colors cells light pink with fine granules and a dark purple, multi-lobed (3-7) nucleus; lifespan 6 hours to a few days

Eosinophils (Lab 1.2 Table 2)

100-400 cells/mm³ (1-4% of WBCs); function in allergic reactions and parasitic infections; staining colors cells red with larger granules, bilobed nucleus stains blue-red; lifespan 8-12 days

Basophils (Lab 1.2 Table 2)

20-50 cells/mm³ (0-1% of WBCs); function in allergic reactions and inflammation, releasing histamine and heparin (anticoagulant); U- or S-shaped dark blue nucleus and cytoplasm with large purple granules; lifespan less than 1 day to a few days

Lymphocytes (Lab 1.2 Table 2)

1,500-3,000 cells/mm³ (20-45% of WBCs); contain cells of the adaptive immune response (B cells that produce antibodies and T cells that destroy infected/tumor cells); large, spherical, dark blue nucleus taking up most of bluish cytoplasm; lifespan weeks to years

Monocytes (Lab 1.2 Table 2)

100-700 cells/mm³ (4-8% of WBCs); phagocytes that become macrophages, increase in chronic infections, activate lymphocytes; bluish-purple kidney- or U-shaped nucleus with blue cytoplasm; lifespan days to months

Complete blood count (CBC)

A commonly ordered blood test used to evaluate overall health and detect a wide range of disorders, including anemia, polycythemia, leukopenia, leukocytosis, thrombocytopenia, and thrombocytosis

Anemia (Lab 1.2 CBC)

Decreased number of RBCs or RBCs with deficiencies in hemoglobin that decreases the oxygen-carrying capacity of the RBCs

Polycythemia (Lab 1.2 CBC)

Increased number of RBCs that can cause thrombosis (blood clotting)

Leukopenia (Lab 1.2 CBC)

Decreased number of WBCs that can cause impaired immunity

Leukocytosis (Lab 1.2 CBC)

Increased number of WBCs that can be indicative of certain blood cancers

Thrombocytopenia (Lab 1.2 CBC)

Decreased number of platelets, causing risk of bleeding

Thrombocytosis (Lab 1.2 CBC)

Increased number of platelets, causing risk of clotting and ischemic injury to organs

RBC Count (CBC feature)

Measures the number of RBCs in a volume of blood; low suggests anemia, high suggests polycythemia or dehydration; reference range Males 4.7-6.1 million/µL, Females 4.2-5.4 million/µL

Hemoglobin (Hgb) (CBC feature)

Measures the protein that carries oxygen; low indicates anemia, high indicates lung disease or living at high altitudes; reference range Males 13.8-17.2 g/dL, Females 12.1-15.1 g/dL

Hematocrit (CBC feature)

Measures the percentage of blood volume made up by RBCs; low indicates anemia, high indicates dehydration or polycythemia; reference range Males 40.7-50.3%, Females 36.1-44.3%

Mean Corpuscular Volume (MCV)

Measures the average size of RBC; low indicates microcytic anemias (iron deficiency or thalassemia), high indicates macrocytic anemia (vitamin B12 or folate deficiency, liver disease); reference range 80-96 fL

Mean Corpuscular Hemoglobin (MCH)

Measures the average amount of hemoglobin per RBC; low indicates hypochromic conditions (iron deficiency anemia, chronic blood loss, thalassemia), high indicates hyperchromic conditions (vitamin B12 or folate deficiency); reference range 27-31 pg/cell

Mean Corpuscular Hemoglobin Concentration (MCHC)

Measures the average concentration or percentage of hemoglobin in RBCs; low indicates hypochromic and microcytic anemias, high indicates hyperchromic conditions; reference range 32-36 g/dL

Red Cell Distribution Width (RDW)

Quantifies the variation in size of red blood cells; high values are indicative of anemias, recent blood transfusion, or hematologic disorders like sickle cell; reference range 11.6-14.6%

White Blood Cell Count (WBC) (CBC feature)

Measures the number of WBCs; low (leukopenia) indicates risk of infection from bone marrow disorders, autoimmune diseases, medications, nutritional deficiencies, or immunodeficiencies; high (leukocytosis) indicates possible infection, inflammation, or cancer; reference range 4,500-11,000 cells/µL

Differential (Diff) (CBC feature)

A count of the different types of WBCs, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils; interpretation depends on the type of leukocyte and whether it is increased or decreased

Platelet Count (CBC feature)

Measures the number of platelets; low (thrombocytopenia) indicates easy bleeding/bruising from bone marrow disorders, autoimmune diseases, medications, or infections; high (thrombocytosis) indicates bone marrow disease, inflammation, infection, or cancer with risk of blood clots; reference range 150,000-450,000 million/µL

Differential white blood cell (WBC) count

A test that measures the percentage of each type of white blood cell present in the blood; a more detailed version of the standard WBC count; used to diagnose infections/disease and their nature (bacterial, viral, parasitic, fungal), and to diagnose/monitor conditions like leukemia or lymphoma

Neutrophils (differential count role)

Usually the most abundant WBC type; first responders to infection, engulfing and destroying pathogens

Lymphocytes (differential count role)

Include B cells, T cells, and natural killer cells; vital for adaptive immune response and defense against viruses

Monocytes (differential count role)

Become macrophages in tissues; involved in phagocytosis and antigen presentation

Eosinophils (differential count role)

Primarily involved in combating parasites and in allergic reactions

Basophils (differential count role)

Least common WBC type; involved in allergic responses and parasite infections

Leukocyte abundance mnemonic

"Never Let Monkeys Eat Bananas" - remembers leukocytes from most to least abundant: neutrophils, lymphocytes, monocytes, eosinophils, basophils