Abnormal Red Cell Morphology

Automated instrumentation in hematology has redefined the level of practice in most hematology laboratories. Along with the complete blood count (CBC), most instruments offer an automated differential count. When values from the differential or CBC are out of the reference range, results are flagged. If a result is flagged, the operator or technologist must make a decision to perform reflex testing or pull a peripheral smear for review or complete differential in order to resolve the abnormal result. Therefore, far fewer peripheral smears are being reviewed or given a complete differential count. Those smears that are scanned or reviewed, however, are from patients who are more seriously ill and may have illness with multiple pathologies. For this reason, proficiency in normal and abnormal identification of red cells is a desirable skill and one that must be practiced as a student or an employee. This section concentrates on defining abnormal red cell morphology and the pathologies that are causative to that morphology. Automated cell counting and differential counters have not yet replaced the well-trained eye with respect to the subtleties of red cell morphology

There is no substitute for a well-distributed, well-stained peripheral smear when assessing red cell morphology. Once this is established, there are two principal questions that must be asked when an abnormal morphology is observed:

1. Is the morphology in every field?

2. Is the morphology artificial or pathological?

Technologists review approximately 10 well-stained and well-distributed fields in a peripheral smear and then make a judgment as to whether anisocytosis (variation in size) and poikilocytosis (variation in shape) are present. If these are present, technologists proceed to record and quantitate those shape and size changes that are responsible for anisocytosis and poik-ilocytosis observation. A numerical scale or qualitative remarks are used to grade the specific morphology. Numeric procedures for assessing red cell morphology can be reviewed in Chapter 20 "Hematology Procedures." What is most important in the assessment of red cell morphology is the discovery of the physiological cause for the creation of that morphology so that the patient can be treated and his or her hematological health restored.

Variations in Red Cell Size

The normal red cell is a disk-shaped structure that is approximately 6 to 8 pm and has an MCV of between 80 and 100 fL and an MCHC of between 32% and 36%. Variations in size are seen as microcytes (less than 6 pm) or macrocytes (greater than 9 pm). Microcytic cells result from four main clinical conditions: iron deficiency anemia, thalassemic syndromes, iron overload conditions, and the anemia of chronic disorders. Microcytic cells are part of the clinical picture in iron deficiency anemia and result from impaired iron metabolism as a result of either deficient iron intake or defective iron absorption.6 Iron is an essential element to the formation of the hemoglobin molecule. The heme portion of hemoglobin is formed from having four iron atoms surrounded by the protoporphyrin ring. Two pairs of globin chains are then assembled onto the molecule with the heme structure lodged in the pockets of the globin chains. Iron needs to be incorporated into the four heme structures of each hemoglobin molecule, and also needs to be absorbed from the bloodstream and transferred, via transferrin, to the pronormoblasts of the bone marrow for incorporation in the heme structure. Iron-starved red cells divide more rapidly than normal red cells, searching for iron, and are smaller because of these rapid divisions. The thalassemic conditions give rise to microcytes owing to decreased or absent globin synthesis. When either alpha or beta chains are missing or diminished, normal adult hemoglobin is not synthesized and hemoglobin configuration is impaired, leading to microcytic cells that have an increased central pallor, known as hypochromia. The

40 Part I • Basic Hematology Principles

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