Erythrocyte-Related Hematological Tests - Knowing Your Blood Health

Introduction

Red blood cells (RBC) called erythrocytes are one of the major cellular components of blood, that carry out the transportation of oxygen and other nutrients in the body. Their specialized cell morphology facilitates their movement in the cardiovascular system and enables them to execute vital functions. Any alteration in the size, shape, and concentration of erythrocytes in blood, is a potential indicator of disease pathogenesis. Therefore, erythrocytes hold a prime position in hematological tests.

What Is the Need for Erythrocyte-Related Hematological Tests?

Evaluation of erythrocytes is the foremost hematological investigation done to assess a person’s healthy state, detect disease pathologies (blood-related and non-blood-related), determine disease progression, and evaluate the prognosis of specific treatments. Multiple characteristics of red blood cells are investigated and analyzed with average standardized values. The commonly evaluated parameters of erythrocytes are red blood cell morphology, total cell count, hemoglobin concentration, and the quality of red blood cells to carry oxygen. These tests are relatively inexpensive and do not require high levels of technical expertise, and also easy accessibility of blood samples makes it an ideal source and first line of diagnosis in any hematological investigation.

What Are the Routinely Done Erythrocyte-Related Hematological Tests?

• Peripheral blood smear.

• Erythrocyte sedimentation rate (ESR).

• Hemoglobin concentration (HB).

• Red blood cell count (RBC count).

• Hematocrit (PCV).

• Red blood cell indices (MCV, MCH, MCHC).

• ABO-blood group typing.

What Does Peripheral Blood Smear Indicate?

The peripheral blood film (PBF) shows the cytology of peripheral blood cells which includes red blood cells, white blood cells, and platelets. Correlating PBF with RBC count and red cell indices helps in the diagnosis of various hematological disorders.

Normal Cell Morphology of Erythrocytes

• Erythrocytes in normal health are biconcave, disk-shaped, and anucleated (without a nucleus) with an average diameter of about 7.5 μm.

• Red cells are pink in color (Rowmanowsky staining method) and show a central pallor (a circular area without staining) because the hemoglobin content of the red cell is located peripherally.

• Erythrocytes of normal size and color (hemoglobin content) are termed normocytic and normochromic.

What Is Erythrocyte Sedimentation Rate?

The rate at which the erythrocytes fall to the bottom of the Westergren tube is termed as erythrocyte sedimentation rate (ESR). The process of falling and forming sedimentation is called rouleaux formation. Females have higher ESR values than males. Also, the ESR value increases with an increase in age.

• Normal Range - Male = ≤15 mm/hr, Female = ≤ 20 mm/hr

• Reduced ESR - Inflammatory conditions such as infections, cancer, or autoimmune conditions.

• Increased ESR - Pregnancy, aging, anemia, RBC abnormalities, kidney disease, low serum albumin, lupus lymphoma, multiple myeloma, rheumatoid arthritis, systemic vasculitis, thyroid disease.

Why Is Hemoglobin Concentration Done?

The main function of erythrocytes is oxygen transport through hemoglobin. A sufficient hemoglobin level is necessary to ensure adequate oxygen supply to the tissues. Any abnormal change of hemoglobin concentration in the blood is a potential indicator for defective oxygen transport, which is easily detected in HB concentration analysis.

• Hemoglobin concentration in blood is denoted as g/dl (grams per decilitre).

• The normal Hb level in males is 14 to 18 g/dl and in females is 12 to 16 g/dl.

• Hemoglobin level is low in anemia (iron deficiency, vitamin B12 deficiency, folate deficiency), bleeding, leukemia, renal failure, liver cirrhosis, hypothyroidism, and thalassemia.

• Hemoglobin level is high in polycythemia vera, lung disease, dehydration, smoking, burns, and excessive vomiting.

What Is RBC Count?

The estimation of the number of red blood cells present in the whole blood volume is called RBC count. Normal RBC count is 4.0 - 5.2 million cells per microliter (cells/mcL). The normal range is slightly higher in males and females. The production of erythrocytes from bone marrow is termed erythropoiesis. Increased RBCs are seen in conditions that enhance erythropoiesis and erythrocytes are decreased during erythropoiesis dysfunction.

• High RBC Count - Smoking, congenital heart disease, cor pulmonale, dehydration conditions, hypoxia, pulmonary fibrosis, Bone marrow disorders, drug-induced (Gentamicin, Methyldopa).

• Decreased RBC Count - Anemia, Bleeding, Radiation therapy, Chronic renal failure, hemolysis, Leukemia, Malnutrition, multiple myeloma, Pregnancy, and drug-induced (chemotherapy, Chloramphenicol, Hydantoins, Quinidine).

What Is Hematocrit?

• Hematocrit is the packed total volume of red blood cells in percentage with the whole blood volume, also called packed cell volume (PCV).

• An increased hematocrit is seen in conditions where total blood volume is decreased such as hemorrhagic shock, dehydration, and polycythemia.

• Decreased values are recorded in conditions leading to increased total body fluid content like anemia, overhydration, kidney failure, and chronic inflammatory conditions.

• Pregnancy shows decreased hematocrit due to an increase in blood volume.

What Are Red Cell Indices?

Red cell indices are blood tests done to estimate the size, quality, and hemoglobin content of red blood cells. These tests are useful in identifying the types and etiology of different types of anemias. Red cell indices include

• Mean corpuscular volume (MCV).

• Mean corpuscular hemoglobin (MCH).

• Mean corpuscular hemoglobin concentration (MCHC).

• Red cell distribution width (RDW).

MCV is done to determine the size of RBC while the hemoglobin content of red blood cells is estimated by MCH and MCHC. Red cell distribution width (RDW) also termed as red cell morphology index is done to analyze and quantify variation in erythrocyte size (anisocytosis). Red cell indices are calculated with the known values of hemoglobin, hematocrit (packed cell volume), and red blood cell count.

• MCV - average cell volume of erythrocytes which defines erythrocyte size is measured in femtoliters. The normal values for MCV = 87 ± 7 fl.

• MCH - mean hemoglobin concentration present in a single red blood cell. Normal MCH value ranges from 27-31 pg (picograms). Decreased MCH is seen in hypochromic anemias.

• MCHC - indicates the amount of hemoglobin per unit volume of the cell. MCHC helps to correlate the hemoglobin concentration with the cell volume. The normal values for MCHC = 34 ± 2 g/dl.

• RDW - the coefficient of variation of the red blood cell volume distribution. The normal value for RDW is 13 ± 1.5%.

According to the size of the red cell, anemias are classified as normocytic (normal MCV), macrocytic (increased MCV), or microcytic (decreased MCV). In spherocytosis, due to the loss of membrane and the consequent spherical shape assumed by the cell, the MCHC has increased.

What Is ABO-Blood Group Typing?

Blood grouping is done based on four erythrocyte phenotypes (A, B, AB, and O). There are two types of cell surface antigens, antigen A and antigen B present in the erythrocytes. Expression (presence/absence) of these surface antigens determines the blood group type. Blood types of individuals receiving blood transfusions are crossmatched with compatible blood group donors to prevent hemolytic reactions. Agglutination of red blood cells occurs in incompatible blood groups triggering adverse immune reactions.

Conclusion

Erythrocyte size, distribution, and variation in size help to identify and assess clinical disease and pathologic processes. In addition, red blood cells and their evaluation also give information about a patient’s general health and physiological processes in the body. Hence, erythrocyte-related hematological tests play a vital role in clinical diagnosis.