Unit 2: Blood Cells - Subjective Questions

Blood cell morphology is the study of the size, shape, structure, staining characteristics, and intracellular features of blood cells as observed under a microscope.

Its importance includes:

• Differentiating normal erythrocytes, leukocytes, and platelets.
• Identifying abnormal cells associated with anemia, leukemia, infection, and other hematological disorders.
• Assessing the size, shape, color, and inclusions of red blood cells.
• Recognizing changes in white blood cell numbers, maturity, and granulation.
• Evaluating platelet size, distribution, and clumping.
• Supporting automated blood-count results and detecting abnormalities that instruments may not classify accurately.

A properly prepared and stained peripheral blood smear is essential for reliable morphological examination.

A mature erythrocyte has the following features:

• It is a biconcave disc with a diameter of approximately to .
• It lacks a nucleus and other cytoplasmic organelles.
• The central area is paler than the peripheral region because of its biconcave shape; this is called central pallor.
• Central pallor normally occupies about one-third of the cell diameter.
• The cytoplasm stains pink to salmon-red with Romanowsky-type stains because of hemoglobin.
• Normal red cells are fairly uniform in size and shape, a condition called normocytosis and normocytosis in shape, respectively.
• They are flexible, allowing them to pass through narrow capillaries.

Anisocytosis refers to variation in the size of red blood cells. It is recognized when small cells, normal-sized cells, and large cells are present together in a smear. It may occur in iron-deficiency anemia, megaloblastic anemia, and mixed nutritional anemia.

Poikilocytosis refers to variation in the shape of red blood cells. It is observed when abnormal forms such as target cells, sickle cells, spherocytes, ovalocytes, or teardrop cells are present.

Microscopically, both conditions are assessed by examining the monolayer region of a well-prepared smear. The findings should be reported according to their degree, such as slight, moderate, or marked.

The size of erythrocytes is judged by comparison with the nucleus of a small lymphocyte or by correlation with the mean corpuscular volume obtained from an analyzer. Size variation may occur simultaneously with shape and color abnormalities.

Hypochromic red cells have an abnormally increased area of central pallor because they contain less hemoglobin. They are commonly small and are often seen in iron-deficiency anemia and thalassemia.

Polychromatophilic red cells appear bluish-gray or grayish-purple on a Romanowsky-stained smear. Their color is caused by residual ribosomal RNA. They usually represent young red cells, or reticulocytes, that have recently entered the circulation.

The presence of polychromatophilia generally indicates increased erythropoietic activity, such as in hemolysis or recent blood loss. Hypochromia indicates reduced hemoglobinization and should be interpreted along with red cell size and other laboratory findings.

Target cells: These cells have a central area of hemoglobin surrounded by a pale ring and an outer hemoglobinized rim, producing a target-like appearance. They may occur in liver disease, hemoglobinopathies, thalassemia, and after splenectomy.

Spherocytes: These are spherical red cells that lack the normal central pallor. They are usually dense and smaller-looking than normal cells. They are commonly associated with hereditary spherocytosis and immune-mediated hemolytic anemia.

Sickle cells: These are elongated, crescent-shaped red cells with pointed ends. They result from polymerization of abnormal hemoglobin under reduced oxygen conditions and are characteristic of sickle cell disease.

• Ovalocytes or elliptocytes: These are oval or elongated red cells. Large numbers may be associated with hereditary elliptocytosis, while smaller numbers can occur in iron deficiency and other anemias.
• Teardrop cells or dacryocytes: These cells have a rounded end and a single pointed end, resembling a teardrop. They may be seen in marrow fibrosis, marrow infiltration, and severe anemia.
• Schistocytes: These are fragmented red cells with irregular shapes, including helmet, triangle, or crescent forms. They suggest mechanical fragmentation, as in microangiopathic hemolytic anemia or disseminated intravascular coagulation.
• Stomatocytes: These cells have a slit-like or mouth-shaped area of central pallor. They may occur as an artifact or in hereditary stomatocytosis, liver disease, and alcohol-related disorders.

Red blood cell inclusions are abnormal structures or residual material observed within erythrocytes.

• Howell–Jolly bodies: These are small, round, deeply basophilic DNA remnants, usually single and located near the cell margin. They may be seen after splenectomy, in hyposplenism, and in megaloblastic anemia.
• Basophilic stippling: This consists of fine or coarse blue-purple granules distributed throughout the red cell. It represents aggregated ribosomal RNA and may occur in lead poisoning, thalassemia, and impaired erythropoiesis.
• Pappenheimer bodies: These are small, irregular, blue-purple iron-containing granules, usually located near the cell periphery. They may be seen after splenectomy and in sideroblastic anemia.

The type and distribution of inclusions can provide useful diagnostic clues.

A normal mature neutrophil measures approximately to in diameter. Its nucleus is dark purple and typically divided into two to five lobes connected by thin chromatin strands. The cytoplasm is pale pink or lilac and contains numerous fine, neutral-staining granules.

The granules include:

• Primary granules, which contain enzymes and antimicrobial substances.
• Secondary granules, which are finer and contain substances such as alkaline phosphatase and lactoferrin.

A normal neutrophil usually has three nuclear lobes. Increased nuclear lobulation is called hypersegmentation and may occur in megaloblastic anemia. Predominance of immature, less-segmented neutrophils is called a left shift and may indicate acute infection or inflammation.

A normal small lymphocyte is approximately to in diameter. It has a large, round to slightly indented nucleus with dense, clumped chromatin. The cytoplasm is scanty and pale blue, often forming a thin rim around the nucleus. Occasional fine azurophilic granules may be present.

A monocyte is larger, approximately to in diameter. It has an irregular, folded, or kidney-shaped nucleus with finer chromatin. Its cytoplasm is abundant, gray-blue, and may contain fine azurophilic granules or vacuoles.

Thus, lymphocytes are generally smaller with dense chromatin and scant cytoplasm, whereas monocytes are larger with abundant gray cytoplasm and a less-condensed nucleus.

Both cells are granulocytes, but their granule color and nuclear visibility allow them to be distinguished microscopically.

Granulocytic maturation is recognized by progressive changes in nuclear shape, chromatin condensation, and cytoplasmic granulation:

• Myeloblast: Large cell with a high nuclear-to-cytoplasmic ratio, fine chromatin, nucleoli, and scant agranular cytoplasm.
• Promyelocyte: Larger cell with primary azurophilic granules and visible nucleoli.
• Myelocyte: Round nucleus without visible nucleoli and development of specific granules.
• Metamyelocyte: Indented or kidney-shaped nucleus with more condensed chromatin.
• Band cell: Curved, horseshoe-shaped nucleus without distinct lobulation.
• Segmented granulocyte: Mature cell with a multilobed nucleus and specific cytoplasmic granules.

Increased immature forms in peripheral blood may indicate a left shift, often associated with acute infection or significant marrow stimulation.

A left shift is an increase in immature neutrophil forms, particularly band cells, metamyelocytes, and occasionally myelocytes, in peripheral blood. It commonly occurs during acute bacterial infection, inflammation, or intense marrow stimulation.

Toxic changes are morphological abnormalities in neutrophils associated with severe infection or inflammation. They include:

• Toxic granulation: Prominent, coarse, dark primary granules.
• Döhle bodies: Pale blue, oval cytoplasmic inclusions composed of rough endoplasmic reticulum.
• Cytoplasmic vacuoles: Clear spaces in the cytoplasm caused by phagocytic activity or degeneration.

These findings should be interpreted together with the white blood cell count, differential count, and clinical condition.

Platelets are small, anucleate cytoplasmic fragments derived from megakaryocytes. Normal platelets are approximately to in diameter. They appear as pale blue fragments with fine reddish-purple granules concentrated in the central region.

On a peripheral smear, platelet abnormalities may include:

• Thrombocytopenia: Reduced number of platelets.
• Thrombocytosis: Increased number of platelets.
• Giant platelets: Platelets approaching the size of a red cell, often indicating increased platelet production or inherited platelet disorders.
• Hypogranular platelets: Platelets with reduced or absent granules.
• Platelet clumps: Aggregates that may cause falsely low automated platelet counts.

Platelet estimation should be performed in the appropriate smear area and correlated with the analyzer result.

Romanowsky stains, such as Leishman, Wright, and Giemsa stains, contain acidic and basic dyes. The acidic dye eosin stains basic cellular components, while basic dyes such as methylene blue and its oxidation products stain acidic components.

The staining effects include:

• Hemoglobin and eosinophilic granules appear pink to orange.
• Nuclear chromatin and basophilic structures appear blue to purple.
• Neutrophil granules appear fine lilac.
• Eosinophil granules appear red-orange.
• Basophil granules appear dark blue-purple.
• Platelets show pale blue cytoplasm with purple granules.

Correct staining allows assessment of cell size, nuclear shape, chromatin pattern, cytoplasmic color, granules, and inclusions. Incorrect pH, staining time, or washing can produce misleading morphology.

The examination should be performed systematically:

1. Select a well-prepared, adequately stained smear.
2. Begin with the low-power objective to assess smear quality, thickness, staining, and distribution of cells.
3. Locate the monolayer or feathered-edge region where red cells are close together but not overlapping excessively.
4. Use the oil-immersion objective to examine erythrocyte size, shape, color, inclusions, leukocyte morphology, and platelet distribution.
5. Perform the differential leukocyte count by identifying cells according to their nuclear and cytoplasmic features.
6. Examine the feathered edge for platelet clumps, abnormal large cells, or parasites.
7. Correlate morphological observations with the complete blood count and clinical information.

Morphology should be reported using standardized terms and graded when appropriate.

In iron-deficiency anemia, the smear commonly shows:

• Microcytosis, or reduced red cell size.
• Hypochromia, with increased central pallor.
• Anisocytosis and poikilocytosis.
• Pencil cells or elliptocytes in some cases.

In megaloblastic anemia, the smear commonly shows:

• Macro-ovalocytes, which are large oval red cells.
• Marked anisocytosis and poikilocytosis.
• Hypersegmented neutrophils with excessive nuclear lobulation.
• Occasional nucleated red cells or other abnormal precursors in severe disease.

The combination of macro-ovalocytes and hypersegmented neutrophils is particularly suggestive of megaloblastic erythropoiesis, whereas microcytic hypochromic cells are characteristic of iron-restricted hemoglobin production.

Morphological evidence of hemolysis may include:

• Polychromatophilia, indicating increased release of young red cells.
• Reticulocytosis, which may be confirmed using a supravital stain.
• Nucleated red blood cells in severe or rapid hemolysis.
• Spherocytes in extravascular immune hemolysis or hereditary spherocytosis.
• Schistocytes in intravascular mechanical fragmentation, such as microangiopathic hemolytic anemia.
• Sickle cells in sickling disorders.
• Bite cells or blister cells in some oxidative hemolytic processes.

These findings must be correlated with reticulocyte count, bilirubin, lactate dehydrogenase, haptoglobin, and other laboratory results.

In acute leukemia, the peripheral smear may show an increased number of immature precursor cells called blasts. Typical blast features include:

• Large cell size with a high nuclear-to-cytoplasmic ratio.
• Fine, open chromatin.
• One or more prominent nucleoli.
• Scant to moderate basophilic cytoplasm.
• Possible cytoplasmic granules in myeloid blasts.
• Auer rods in some myeloid blasts, appearing as reddish-purple needle-like inclusions.

The smear may also show anemia, thrombocytopenia, and abnormal mature leukocyte forms. A definitive classification cannot be made from morphology alone and requires cytochemistry, immunophenotyping, cytogenetics, or molecular testing.

A normal lymphocyte is usually small, with a round nucleus, dense clumped chromatin, and scant pale blue cytoplasm.

A reactive lymphocyte is generally larger and more variable in shape. It may have:

• Abundant deeply basophilic cytoplasm.
• Cytoplasmic edges that appear to flow around adjacent red cells.
• A round, oval, indented, or irregular nucleus.
• Less-condensed chromatin and occasional nucleoli.
• Occasional vacuoles or uneven cytoplasmic staining.

Reactive lymphocytes are commonly associated with viral infections and other immune stimulation. They should not be confused with blast cells, which usually have finer chromatin, prominent nucleoli, and a more immature overall appearance.