Definition and Use
- The RBC count is part of the CBC as obtained by automated counters. It is less useful than the Hb or Hct.
- Normal range: 4.2 " “5.4 cells/ Ž ¼L in women and 4.4 " “6.0 cells/ Ž ¼L in men (reported by automated counters in a random adult population)
- Different values are reported for newborns, infants, and children until they reach adulthood.
- Automated counters adjust normal values for age groups.
Interpretation
- The RBC count is interpreted in conjunction with red cell indices, hemoglobin, and hematocrit.
Increased In
- Certain myeloproliferative neoplasms (e.g., polycythemia vera).
- Severe dehydration. RBC counts may be appropriately decreased or increased in certain physiologic states.
Decreased In
Abnormal RBC Morphology
- It is flagged by automated counters, triggering microscopic examination of stained peripheral blood smears (see above).
- Abnormalities (see Tables 16.72 and 16.73) may be specific for certain conditions (e.g., spherocytes for hemolytic anemias, sickle cells for sickle cell anemias) or may be informative but not specific. Anisocytosis refers to variation in RBC size, poikilocytosis refers to variation in shape, and polychromasia refers to bluish discoloration of RBC reflecting high reticulocytes.
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TABLE 16 " “72Abnormal Shapes of Red Blood CellsView LargeTABLE 16 " “72Abnormal Shapes of Red Blood Cells Shape Description Conditions Acanthocytes (spur cells) Pointed membrane spicules of uneven length Hereditary: acanthocytosis in abetalipoproteinemia Acquired: postsplenectomy, fulminant liver disease, malabsorption Bite cells (precipitated hemoglobin [Heinz bodies]) RBCs with a peripheral smooth semicircle fragment missing Hemolysis due to certain drugs, with or without G6PD deficiency; unstable hemoglobin Burr cells Crenated RBCs with preserved central pallor Uremia, liver disease, Rhesus factor null cells, phosphokinase deficiency, anorexia nervosa, hypophosphatemia, hypomagnesemia, hyposplenism Echinocytes Blunt uniform spicules Similar to burr cells; may be artifacts Elliptocytes/ovalocytes Oval RBCs Hereditary elliptocytosis, iron deficiency, sickle cell trait, thalassemias, HbC disease; megaloblastic anemias HbC crystalloids Rhomboid crystals inclusions in RBCs HbC trait or disease Leptocytes Flat, water-like, thin, hypochromic RBCs Obstructive liver disease, thalassemia Macrocytes RBCs larger than normal, well filled with hemoglobin Oval macrocytes in megaloblastic anemias; round macrocytes in liver disease Increased erythropoiesis Microcytes Decreased MCV (RBC smaller than normal) Hypochromic anemias with defective iron stores Microspherocytes Artifacts; severe frostbite RBC agglutination Grouping together of RBCs due to IgM antibodies Cold agglutinins, most commonly Mycoplasma pneumoniae; infectious mononucleosis Rouleaux formation Stack of coins appearance Hyperproteinemias, especially multiple myeloma and plasmacytic lymphoma of IgM type; most frequently artifact Schistocytes (mechanical destruction of RBC in the circulation) Helmet-like or fragmented, distorted RBCs Micro- or macroangiopathic (small or large arteries) hemolytic anemias, prosthetic heart valves, severe valvular disease or large atheromas, DIC, TTP, severe iron deficiency, megaloblastic anemias, severe burns, renal transplant rejection, postchemotherapy, snake bite, inherited abnormalities of RBC membrane spectrin Sickle cells (drepanocytes) Bipolar, spiculated RBCs, pointed at both ends (shaped like sickles) Sickle cell anemia (absent in sickle cell trait, unless induced by oxygen reduction) Spherocytes (loss of RBC membrane) Increased MCHC, usually decreased MCV; spherical cells with dense appearance and without central pallor Hereditary spherocytosis, autoimmune hemolytic anemias, recent RBC transfusion Stomatocytes Mouth-like deformity with slit-like central pallor Hereditary stomatocytosis, Rhesus factor null disease, immune hemolytic anemia, acute alcoholism, certain drugs (phenothiazines); frequently artifacts Target cells (increased ratio of RBC surface area to volume) Target-like appearance, often hypochromic; decreased osmotic fragility Thalassemias, HbC disease or trait, HbD and E, iron deficiency anemia, liver disease, postsplenectomy, artifacts Teardrop cells (dacryocytes) Distorted, teardrop-shaped RBCs Primary myelofibrosis, myelophthisic anemia, other myeloproliferative neoplasms or myelodysplastic syndromes, Ž ²-thalassemia major, iron deficiency, conditions with Heinz bodies
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TABLE 16 " “73Red Blood Cell InclusionsView LargeTABLE 16 " “73Red Blood Cell Inclusions Red Cell Type Description Disease State Association Basophilic stippling Punctuate basophilic inclusions composed of precipitated ribosomes (RNA) A variety of anemias, thalassemias; coarse in lead poisoning Cabot rings Circular, blue, thread-like inclusion with dots Occasional in severe megaloblastic and hemolytic anemias, overwhelming infections, postsplenectomy Heinz bodies Precipitates of denatured hemoglobin attached to RBC membrane; require supravital stains (e.g., crystal violet) for visualization G6PD deficiency, methemoglobin reductase, drug-induced hemolytic anemias, unstable hemoglobin (e.g., hemoglobin Zurich), postsplenectomy; can be artifactual Howell-Jolly bodies Nuclear remnants of DNA; one, rarely two, dark purple, nonrefractile spherical bodies located at periphery of RBCs Postsplenectomy, megaloblastic anemias, thalassemia, myelodysplasia, lead poisoning Organisms on smears, outside RBCs Specific morphology Wuchereria bancrofti; Brugia malayi; Loa loa; Trypanosoma brucei gambiense, T. cruzi, and T. rhodesiense; Borrelia recurrentis Organisms within RBCs Specific shapes Plasmodium trophozoites, babesiosis, other organisms Pappenheimer bodies Siderotic, nonheme iron granules at periphery of RBC; seen best with Prussian blue stain Sideroblastic anemias, iron load, thalassemia, lead poisoning, postsplenectomy
Limitations
- Patients circumstances (e.g., vomiting or diarrhea)
- Other preanalytic factors
- Marked leukocytosis marginally increases the RBC count.
- Inappropriate blood collection is a major source of preanalytic errors. For instance, inappropriate filling of test tube results in excess anticoagulant, thereby diluting the blood and decreasing the red cell parameters.
- Very low temperatures may lyse the red cells. Anticoagulated blood may be stored at 4 ‚ °C for 24 hours, but beyond this interval, the results become increasingly altered.