In this article we will discuss about the morphologic abnormalities of red blood cells, white blood cells and platelets.
Morphologic Abnormalities of Red Blood Cells (RBC):
i. Basophilic Stippling:
Basophilic stippling is the occurrence of fine, medium, or coarse blue granules uniformly distributed throughout some red blood cells. Fine stippling may be associated with polychromatophilia, while coarse stippling usually indicates impaired erythropoiesis.
Heavy metal poisoning (e.g. lead and arsenic), hemoglobinopathies, thalassemias, sideroblastic anemias, pyrimidine-5′-nucleotidase deficiency, and other diseases should be excluded when coarse basophilic stippling is found.
ii. Bite Cells:
Bite cells (degmacytes) are RBCs with peripheral single or multiple arcuate defects (“bites”). They are usually accompanied by at least a few blister cells (RBCs with vacuoles or markedly thin areas at periphery of membrane), acanthocytes, and schistocytes. Bite cells are associated with oxidant stress to the red blood cell.
They can be found in normal individuals receiving large quantities of aromatic drugs (or their metabolites) containing amino, nitro, or hydroxy groups, or in patients with red-cell enzymopathies involving the pentose phosphate shunt (most notably G-6-PD deficiency, pyruvate kinase deficiency) during acute hemolytic episodes following exposure to oxidant stress. If indicated, a Heinz body test, G-6-PD level, and other studies of red blood cell metabolism may be indicated.
iii. Blister Cells:
Blister cells are red blood cells with vacuoles or markedly thin areas at periphery of membrane. These cells are characteristic of glucose-6-phosphate dehydrogenase (G-6-PD) deficiency and other conditions imposing oxidant stress on the erythrocyte.
iv. Codocytes:
Codocytes (“target cells”) are thin, hypochromatic cells with a round area of central pigmentation. Codocytes are characteristically seen after splenectomy, and in patients with thalassemia, and certain hemoglobinopathies (hemoglobin SS, SC, CC, EE, AE, sickle cell-thalassemia).
They are also found in association with iron deficiency anemia, liver disease, and familial lecithin-cholesterol acyltransferase (LCAT) deficiency. If indicated, hemoglobin electrophoresis, liver function evaluation, serum iron studies, serum lipid profile and/or other studies may be indicated.
v. Dacrocytes:
Dacrocytes (“tear drop cells”) are red blood cells in the shape of a teardrop. Microcytosis and hypochromia usually accompany them. Dacrocytes are characteristically seen in relatively large numbers in patients with myelophthisic anemia (particularly myelofibrosis with myeloid metaplasia), but can be found in moderate numbers in megaloblastic anemia, beta-thalassemia, renal failure, tuberculosis, Heinz body disease, acquired hemolytic anemia, hypersplenism, and other hematologic diseases. Teardrop cells are pathologic and usually indicate significant bone marrow dysfunction. Clinical correlation and patient follow up is essential.
vi. Drepanocytes:
Drepanocytes (“sickle cells”) are curved, irregular red blood cells with pointed ends, which are characteristic of the “sickle” hemoglobinopathies. Diseases with Hb S (sickle cell anemia, hemoglobin SC disease, hemoglobin S-beta-thalassemia, hemoglobin SD disease, hemoglobin Memphis/S disease) are the usual cause, but drepanocytes can also be seen in other hemoglobinopathies (especially Hb I, Hb C-Harlem, Hb C Capetown). A sickle cell screen and/or hemoglobin electrophoresis may be indicated.
vii. Echinocytes/Burr Cells:
Echinocytes (“sea urchin cells”) are red blood cells with multiple tiny spicules (10-30) evenly distributed over the cell surface. These cells result from exposure of the red cell to fatty acids, lysolecithin, amniotic compounds, elevated pH, and other substances.
They occur post-splenectomy, after the administration of heparin, in the hemolytic-uremic syndrome, and in hepatitis of the newborn, pyruvate kinase deficiency, phosphoglycerate kinase deficiency, uremia, and malabsorption states.
Burr cells (“crenated cells”) are similar in appearance, but show an uneven distribution of spicules. Burr cells are characteristically seen in uremia, where they represent damaged or fragmented red blood cells.
viii. Elliptocytes:
Elliptocytes are cells with an elliptical shape, while ovalocytes have an oval shape. Severe elliptocytosis (> 10% elliptocytes) is characteristic of hereditary elliptocytosis, but can be prominent in thalassemia, sickle cell trait, and Hb C trait.
Elliptocytic hemolytic anemia (< 10% has been reported in association with cirrhosis, decreased erythrocyte glutathione, and with glucose-6-phosphate deficiency. Other diseases where elliptocytosis occurs include iron deficiency anemia, megaloblastic anemia, myelophthisic anemia, and mechanical trauma.
Rare elliptocytes (< 1%) occur in normal peripheral blood smears. If clinically indicated, osmotic fragility evaluation, hemoglobin electrophoresis, and studies of red blood cell metabolic activity may be indicated for further evaluation of patients with elliptocytosis.
ix. Howell-Jolly Bodies:
Howell-Jolly bodies are small (1 mm) dense, perfectly round basophilic red cell inclusions which represent nuclear material derived from nuclear fragmentation (karyorrhexis) or incomplete nuclear expulsion during normoblastic maturation.
Howell-Jolly bodies produced in non-diseased individuals are effectively removed by the spleen and are not visible in the circulation. However, Howell-Jolly bodies are readily identified in splenectomized patients and may also be seen in smaller numbers in patients with megaloblastic anemia, severe hemolytic processes, hyposplenism, and myelophthisitic anemia.
x. Hypochromia:
Hypochromia is a decreased amount (MCH) and concentration (MCHC) of hemoglobin in red blood cells. In the peripheral blood smear, hypochromic cells have an expanded central zone of pallor. Small hypochromic red blood cells (microcytes) are usually present, and the mean corpuscular volume (MCV) is decreased.
Microcytosis and hypochromia are characteristic of iron deficiency anemia and other microcytic, hypochromic anemias [anemia of chronic disease], hereditary hemoglobinopathies with diminished globin synthesis (thalassemias, hemoglobin E, hemoglobin H), red blood cell enzyme deficiencies (sideroblastic anemias, lead poisoning, pyridoxine deficiency).
Serum iron studies, erythrocyte sedimentation rate (ESR), hemoglobin electrophoresis, bone marrow examination, and serum and urine lead quantitation are other laboratory studies may be indicated.
xi. Hyperchromia:
Hyperchromia is an increase in the red blood cell hemoglobin concentration (MCHC > 36 g/dL). Since it is usually associated with spherocytosis, peripheral smear examination reveals many spherocytes and microspherocytes.
Consideration of hereditary spherocytosis is recommended, but spherocytes are also seen in patients with isoimmune and autoimmune hemolytic anemias, Heinz body hemolytic anemia, hereditary pyropoikilocytosis, and severe burns. If indicated, an osmotic fragility assay, Coombs’ test, serum bilirubin, LDH, and haptoglobin, and other laboratory assays may be indicated.
xii. Keratocytes/Schistocytes:
Keratocytes (“horn cells, helmet cells”) and schistocytes (“fragmented cells”) are damaged red blood cells. Such damage characteristic occurs from fibrin deposits (DIC, microangiopathic hemolytic anemia, thrombotic thrombocytopenic purpura (TTP), prosthetic heart valves, severe valvular stenosis, malignant hypertension, or March hemoglobinuria.
However, keratocytes and schistocytes also occur in normal newborns and in patients with bleeding peptic ulcer, aplastic anemia, pyruvate kinase deficiency, vasculitis, glomerulonephritis, renal graft rejection, severe burns, iron deficiency, thalassemia, myelofibrosis with myeloid metaplasia, hypersplenism and post-splenectomy, and other diseases. Clinical correlation is recommended, with the appropriate diagnostic studies. These cells are pathologic and should never be ignored.
xiii. Knizocytes:
Knizocytes (“pinch bottle cells”) are characteristically seen in patients with hemolytic anemia, including hereditary spherocytosis. An osmotic fragility assay, Coombs’ test, serum bilirubin, LDH, and haptoglobin, and other laboratory assays may be indicated.
xiv. Macrocytes:
Oval macrocytes (“macroovalocytes, megalocytes”) are large oval red blood cells (> 8.5 mm) with an elevated MCV (> 100 fL, frequently > 120 fL) and normal MCH. The presence of these cells suggests impaired bone marrow DNA synthesis, and may indicate a vitamin B19 or folate deficiency. Serum vitamin B12 or folate levels are usually indicated and a bone marrow examination may be needed.
Round macrocytes are slightly to moderately larger than normal (macrocytosis, MCV > 95 fL but usually < 120 fL) and are round in shape. This finding suggests impaired bone marrow impaired DNA synthesis, stress erythropoiesis, or excessive surface membrane.
Possible clinical causes include liver disease (obstructive jaundice, alcoholism), impaired DNA synthesis from chemotherapy or inherited diseases, myeloproliferative disorders, myelodysplastic syndromes, or splenectomy. Bone marrow examination, liver function studies, and other laboratory assays if clinically indicated.
xv. Microcytes:
Microcytes are small red blood cells (MCV < 80 fL) with decreased amounts of hemoglobin formed as a result of iron deficiency and defective hemoglobin synthesis, imbalance of globin chains, or defective porphyrin synthesis. Possible clinical causes of microcytosis include iron deficiency anemia, thalassemia, the anemia of chronic disease, lead poisoning, and sideroblastic anemias.
xvi. Nucleated Red Blood Cells:
Nucleated red blood cells (NRBCs, normoblasts) are immature red blood cells. In an adult, the presence of NRBCs indicates markedly accelerated erythropoiesis and/or severe bone marrow stress. Clinical conditions associated with peripheral normoblastosis include acute bleeding, severe hemolysis, myelofibrosis, leukemia, myelophthisis, and asplenia.
The presence of NRBCs in the peripheral blood of an adult always indicates a significant disease process, the etiology of which must be delineated. NRBCs in the peripheral blood of an infant indicates significant stress but does not have the ominous significance of features of those in an adult.
xvii. Poikilocytosis:
Poikilocytosis is variation in red blood cell shape, seen in many disorders.
xviii. Polychromasia:
Polychromasia (“polychromatophilia”) is the occurrence of slightly immature red blood cells, which are larger than normal (increased MCV) and have a blue-gray coloration. Polychromasia is due to the presence of ribosomal protein in immature red blood cells, which pick up the basophilic component of the Wright-Giemsa stain.
Small numbers of these cells (0.5 – 2%) are normally present in the peripheral blood and signify the presence of erythropoietic activity in the bone marrow. They are increased in states of increased erythropoietic activity in response to anemia or the iatrogenic administration of erythropoietin or another marrow stimulatory agent. The MCV may increase slightly in response to significant polychromasia. Decreased polychromasia is seen with hypoproliferative marrow states.
xix. Spherocytes:
Spherocytes are small (< 6.5 mm), dense spheroidal RBCs with normal or decreased MCV and absent central pallor. Hereditary spherocytosis is likely if large numbers of spherocytes are present and other forms of abnormal RBCs are absent.
Small numbers of spherocytes, in combination with other abnormal RBCs, are seen in patients with isoimmune and autoimmune hemolytic anemias, Heinz body hemolytic anemia, hereditary pyropoikilocytosis, microangiopathic hemolytic anemia, hypersplenism and post-splenectomy, myelofibrosis with myeloid metaplasia, hemoglobinopathies, malaria, liver disease, recent transfusions, and severe burns. An osmotic fragility assay, Coombs’ test, serum bilirubin, LDH, and haptoglobin, and other laboratory assays may be indicated.
xx. Stomatocytes:
Stomatocytes are uniconcave red blood cells with a slit-like area of central pallor. A predominance of stomatocytes is characteristic of hereditary stomatocytosis (a type of hemolytic anemia).
Small numbers of stomatocytes (usually in association with other abnormal RBCs) occur in patients with acute alcoholism, cirrhosis, obstructive liver disease, advanced malignancy, severe infections, Rhnull disease, treated acute leukemia, and other diseases.
Morphologic Abnormalities of White Blood Cells (WBC):
i. Alder-Reilly Granules:
Alder-Reilly granules are large, coarse, dark purple, azurophilic granules that occur in the cytoplasm of most granulocytes. These are characteristically found in the Alder-Reilly anomaly and in patients with mucopolysaccharidoses.
ii. Auer Rods:
Auer rods are needle- or rod-shaped, eosinophilic structures which occur in the cytoplasm of immature leukocytes (blasts) and more mature cells in some patients with acute myelogenous leukemia (AML).
These structures are formed from coalescing primary (azurophilic) granules. Although Auer rods occur singly in AML FAB subtypes M1, M2, and M4, cells with numerous Auer rods are common in the hyper-granular form of AML FAB M3 to form “faggot” cells.
iii. Chédiak-Higashi Granules:
Chédiak-Higashi granules are very large red or blue granules that appear in the cytoplasm of granulocytes, lymphocytes, or monocytes in patients with the Chédiak- Steinbrinck-Higashi syndrome.
iv. Döhle Bodies:
Döhle bodies are variably sized (0.1 to 2.0 µm) and shaped, blue or grayish-blue cytoplasmic inclusions usually found near the periphery of the cell. Dohle bodies are lamellar aggregates of rough endoplasmic reticulum, which appear in the neutrophils, bands, and metamyelocytes of patients with infection, burns, uncomplicated pregnancy, toxic states, or during treatment with hematologic growth factors such as G-CSF.
v. May-Hegglin Anomaly:
Neutrophils contain small basophilic cytoplasmic granules-which represent aggregated ribosomes. Leukopenia and large platelets are also found. An autosomal dominant trait, the May-Hegglin anomaly is associated with a mild bleeding tendency, but not by an increased susceptibility to infection.
vi. Neutrophilic Hypergranulation (Toxic Granulation):
Small dark blue to purple granules resembling primary granules appear in the cytoplasm of methmyelocytes, bands, and segmented neutrophils during inflammatory states, burns, and trauma, and upon exposure to hematopoietic growth factors such as granulocyte-colony stimulating factor (G-CSF).
Toxic granulation is usually accompanied by a “shift to the left” in the neutrophilic population, and by the presence of vacuolations in the cytoplasm (toxic vacuolations) and Dohle bodies.
vii. Neutrophilic Hyper-Segmentation:
Increased lobulation of granulocyte nuclei (neutrophilic hyper-segmentation) is a characteristic finding in megaloblastic anemia, but can also be seen as an inherited autosomal dominant trait (hereditary hyper-segmentation of neutrophils).
viii. Neutrophilic Hypo-Segmentation:
Single or bi-lobed neutrophils (Pelger-Huet cells) can be inherited (Pelger-Huet anomaly), or acquired (pseudo-Pelger-Huet cells) in patients with malignant myeloproliferative disorders (including preleukemia and myelodysplastic syndromes) and infections or tumors which have metastasized to the bone marrow.
Large, purple or dark-blue azurophilic granules in the cytoplasm of neutrophils, bands, and metamyelocytes are characteristically seen in patients with severe infection, septicemia, toxic states, and chemical poisoning. Cytoplasmic vacuolation is seen as well.
Morphologic Abnormalities of Platelets:
i. Clinical Importance of Platelet Morphology:
Light microscopy is of greatest value in confirming the automated platelet count and performing a manual differential count in patients with very high or very low platelet counts where automated counting is inaccurate. However, care morphologic evaluation may reveal abnormalities which can support other observations.
ii. Classification of Platelet Morphologic Abnormalities:
a. Platelet Hypogranularity:
Many small, reddish-purple granules are normally present in the cytoplasm of the platelet. These granules, which vary in size and shape, represent dense bodies, alpha-bodies, and lysosomes. Hypo-granular platelets, as the name implies, have little, if any, of the purple-red granules found in normal platelets.
These granules may be decreased in number or absent in patients with myeloproliferative diseases and myelodysplastic syndromes. In these disorders, platelet hypo-granulation is usually accompanied by abnormalities in platelet size and shape, anemia, leukocytosis or leukopenia, and abnormalities in leukocyte morphology.
b. Large and Giant Platelets:
Platelets are normally 1.5 to 3 microns in diameter. However, platelet size can increase in patients with increased platelet turnover from bleeding or stress, and in the myeloproliferative and myelodysplastic disorders. Large platelets are 3 to 7 microns (roughly the diameter of a normal RBC), while giant platelets are larger than red cells. Morphology may appear normal or abnormal.
c. Platelet Satellitism:
In this unusual phenomenon, normal platelets adhere to the surface of neutrophils, or, rarely monocytes, to form “platelet rosettes.” Platelet satellitism is associated with blood specimen’s anti-coagulated with EDTA, and disappears when heparin – anti-coagulated blood is collected from the same patient.
Although an innocuous finding, significant platelet satellitism may cause spurious thrombocytopenia, since the cell-bound platelets are not counted with the platelet fraction of the blood specimen.