Hematology Study: Blood Cells Overview

Hematology

• Study of blood cells.
• Includes red blood cells, white blood cells, and platelets.

Red Blood Cells (RBCs)

• Carry oxygen throughout the body.
• Measured in a complete blood count (CBC) using a RBC count, which is the number of cells per cubic millimeter.
• Hemoglobin is the primary constituent of RBC cytoplasm.
• Hematocrit is the ratio of the volume of packed RBCs to the volume of whole blood, measured as a percentage or decimal.

White Blood Cells (WBCs)

• Cells of the immune system.
• Measured in a complete blood count (CBC).
• Leukopenia is a decreased WBC count.
• Leukocytosis is an increased WBC count.
• Differential count reviews and tabulates 100 WBCs on a stained peripheral blood film.
• Types of WBCs include neutrophils, eosinophils, monocytes, basophils, and lymphocytes.

Neutrophils

• Phagocytes for bacteria.
• Have multilobed nuclei (2-5 lobes).
• Their cytoplasm is pink/lavender.
• Neutrophilia is an increase in neutrophils, often caused by bacterial infection.
• Neutropenia is a decrease in neutrophils.
• Band neutrophils are less mature neutrophils with no lobes, shaped like a U or S.

Eosinophils

• Phagocytes for parasites.
• Their cytoplasmic granules are bright orange-red due to proteins.
• Eosinophilia is an increased number of eosinophils, often caused by a parasitic infection.

Basophils

• Secrete histamine and do not phagocytize.
• Their cytoplasmic granules are dark purple, irregular, and obscure the nucleus.
• Basophilia is an increase in basophils.

Lymphocytes

• Phagocytes for viruses.
• The smallest WBCs.
• Types include T cells, B cells, and natural killer cells.
• Provide immunity through cell-mediated and humoral immunity.
• Lymphocytosis is an increased number of lymphocytes, often caused by a viral infection.
• Lymphocytopenia is a decreased number of lymphocytes.

Monocytes

• The biggest WBCs.
• Their cytoplasm is blue-gray with fine azure granules, and their nucleus is usually indented or folded.
• Monocytosis is an increased number of monocytes, often caused by a chronic infection.
• Monocytes are immature macrophages in the blood, becoming macrophages when they go to the tissues.

WBC Order from Most to Least Common

• N-L-M-E-B (neutrophils, lymphocytes, monocytes, eosinophils, basophils).

Platelets (Thrombocytes)

• Cell fragments responsible for primary hemostasis (the initial step in blood clotting).
• Their count determines the number of platelets per cubic millimeter.
• Mean platelet volume (MPV) determines the average size of platelets.
• Thrombocytosis is an increase in platelets.
• Thrombocytopenia is a decrease in platelets.

Coagulation

• Refers to secondary hemostasis, the complex process involving clotting factors.
• Coagulation tests include prothrombin time (PT), partial thromboplastin time (PTT, aPTT), thrombin time, fibrinogen assay, and D-dimer assay.

Microbiology

• The study of microorganisms.
• Involves detection of pathogens from patient samples.

Gram Stain

• Also known as a differential stain.
• Used to select appropriate antimicrobial therapy.
• Uses crystal violet as the primary stain, gram iodine as the mordant, acetone-alcohol as the decolorizer, and safranin as the secondary stain.

Gram-Positive Organisms

• Stain purple.
• Include staphylococcus and streptococcus (cocci), and bacillus (bacilli).

Gram-Negative Organisms

• Stain red.
• Include neisseria (cocci), escherichia (coccobacilli), and pseudomonas (bacilli).

Acid-Fast Stain

• Used for organisms with high lipid and wax content, like Mycobacterium tuberculosis.
• Uses carbon fuchsin as the primary stain, heat (Ziehl-Neelsen) or detergent/tergitol (Kinyoun) as the mordant, acid-alcohol as the decolorizer, and methylene blue or malachite green as the secondary stain.

Direct Sputum Smear Microscopy (DSSM)

• Used to detect infectious cases, particularly tuberculosis.

10% Potassium Hydroxide (KOH)

• Used to detect fungal elements in clinical specimens.
• Clears the specimen of proteinacious and keratinous substances.

Nonselective Media

• Culture media that supports the growth of most nonfastidious microbes.
• Blood agar can be used for hemolysis, resulting in beta (complete, clear zone), alpha (incomplete, grainy zone), or gamma (no hemolysis).