Basophilic Stippling in Red Blood Cells - Causes, Diagnosis, and Significance

Introduction

Basophilic stippling is a clinically significant inclusion of red blood cells that are observed in peripheral blood smears. The presence of basophilic stippling in circulating red blood cells indicates hematologic disorders or toxicities. This finding is related to specific types of acquired and heritable hematologic diseases that affect the production and development of red blood cells.

How Does a Normal Red Blood Cell Appear?

Red blood cells (RBCs) are the predominant functional components of blood that are responsible for the transport of oxygen and nutrients throughout the body. RBCs are specialized cells with a unique shape, structure, and composition which facilitate carrying out such essential functions. It is evident that various diseases, nutritional deficiencies, and toxicities alter the normal integrity of red blood cells and interfere with their functions. These structural changes in RBCs play a crucial role in detecting the relevant disorders. To understand the alterations in RBCs during a disease state, it is essential to know its normal architecture.

Characteristics of a Healthy Red Blood Cell

• A mature RBC is biconcave and discoid.

• It is anucleated (does not have a nucleus).

• The major portion of its cytoplasm is occupied by hemoglobin, a protein molecule that helps in oxygen transport.

• The cytoplasm of RBCs does not contain any organelles (structures inside a cell) and nuclei to accommodate hemoglobin. Thus the presence of any additional structures in RBC is suggestive of a pathological state.

• Organelles and nuclei are present in the early stages of RBC development (in bone marrow) but are lost during their maturation and not seen in circulating blood.

• Its membrane is regular and circular under microscopic examination. Irregularity in the cell membrane also indicates disease conditions.

What Is Basophilic Stippling?

Basophilic stippling is abnormal inclusions of red blood cells that accumulate within the cell during pathological conditions. These inclusions are minute, compact, membrane-bound granules containing specific cellular products. The term basophilic refers to the similar appearance of granules in basophils (a type of white blood cell). Basophilic stippling is one of the clinically important erythrocyte (RBC) inclusions that are usually seen in the microscopic examination of peripheral blood smears.

When Does Basophilic Stippling Occur?

Basophilic stippling is a common indication of the presence of hematologic diseases. It is normally observed in the peripheral blood examination and also occasionally in bone marrow aspirates. Basophilic stippling occurs in various blood-related diseases as well as other disorders, and heavy metal toxicities. The frequent causes for the occurrence of basophilic stippling are as follows:

• Lead poisoning.

• Hemoglobinopathies.

• Nutritional deficiencies.

• Myelodysplastic syndromes.

• Thalassemia.

• Megaloblastic anemia.

• Hemolytic anemias such as sickle cell anemia.

• Infections.

• Liver disease.

• Chronic alcohol use.

• Poisoning by other heavy metals.

• Unstable hemoglobins.

• Pyrimidine-5′-nucleotidase deficiency.

• Hereditary nonspherocytic hemolytic anemias or enzymopathies.

How Is Basophilic Stippling Formed?

Basophilic stippling is formed by the accumulation of abnormal granules inside the cytoplasm of the red blood cells. These abnormal granules are ribonucleic acid (RNA) fragments that get deposited in the cytoplasm of circulating red blood cells. The following sequelae lead to the formation of basophilic stippling in RBCs.

• Ribosomes are cell organelles where protein synthesis takes place. They use ribonucleic acid (RNA) for making proteins.

• These organelles are present in normal immature red blood cells to synthesize proteins that are essential for the maturation of red blood cells..

• These ribosomes and remaining RNA fragments normally get degraded by enzymatic activities in the final stages of RBC maturation and the mature circulating RBCs do not contain any residual cellular particles.

• However, hematological disease conditions and heavy metals like iron interfere with the clearance of ribosomes and RNA remnants by deactivating the specific enzymes in the later phases of RBC maturation.

• Incomplete and failure of ribosomal and RNA degradation leads to the precipitation of residual RNA and ribosomal remnants in the cytoplasm of mature red blood cells present in the circulation.

• The formation of basophilic stippling is attributed to the aggregates of these ribosomes and ribosomal RNA fragments precipitated all over the cytoplasm of circulating red blood cells.

What Are the Samples Collected to Detect Basophilic Stippling?

• Whole blood collected with anticoagulant (potassium EDTA) is the preferred specimen to visualize basophilic stippling.

• The peripheral blood smear is prepared from the collected blood sample and stained using Wright-Giemsa stain to view under light microscopy.

• Bone marrow aspirates are also stained with Wright-Giemsa stain to demonstrate basophilic stippling.

How Is Basophilic Stippling Diagnostically Demonstrated?

The morphology (physical appearance) of basophilic stippling is visualized under light microscopy and electron microscopy. It does not require pacific immunomarkers or sophisticated staining techniques for its identification.

• Basophilic stippling is also called punctate basophilia because of its dotted appearance on the RBCs.

• The stippling is seen as irregular basophilic granules with varying textures from fine to coarse particles under light microscopy.

• The affected red blood cells show tiny, round, purplish blue (basophilic) or dark blue-purple punctated inclusions.

• The inclusions do not cluster and are scattered diffusely in an even distribution throughout the cytoplasm of the RBCs.

• The texture of the inclusions (fine or coarse) depends on the underlying disorder.

• Under electron microscopy, stippled material of ribosomes and RNA fragments are seen along with other ultrastructural details.

What Is the Clinical Significance of Basophilic Stippling?

Various hematologic disorders disrupt the production of red blood cells (erythropoiesis) and erythrocyte (RBC) maturation, which becomes a potential cause for the appearance of basophilic stippling in peripheral smears.

• Coarse basophilic stippling is seen in heavy metal toxicity, especially in lead poisoning.

• In lead toxicity, pyrimidine-5'-nucleotidase (the enzyme needed for ribosomal degradation) is inhibited by lead, and the degradation of ribosomes and ribosomal RNA in circulating RBCs is blocked.

• These residual ribosomes and RNA fragments accumulate as coarse basophilic stippling in lead poisoning.

• Basophilic stippling is a pathognomonic clinical finding in lead poisoning.

• Toxic levels of zinc and other heavy metals also produce coarse basophilic stippling.

• Basophilic stippling is also demonstrated in iron toxicity where red blood cells accumulate excess iron in the plasma forming siderocytes.

• Coarse stippling is also seen in disorders associated with impaired hemoglobin synthesis (thalassemia), in nutritional deficiencies (megaloblastic anemia), and other forms of severe anemia (hereditary nonspherocytic hemolytic anemias).

• In these conditions, coarse-appearing basophilic stippling is attributed to defective instability of RNA in young impaired red blood cells.

• In hemolytic anemias such as sickle cell anemia, the presence of basophilic stippling is related to increased RBC hemolysis and premature release of red blood cells before completing maturation.

• Faulty production and synthesis of red blood cells (erythropoiesis and hematopoietic stem cell differentiation) in conditions like myelodysplastic syndrome also show basophilic stippling due to morphological defects in the RBCs produced.

• Fine basophilic stippling is commonly associated with increased RBC production (polychromatophilia) or sometimes occurs as an artifactual error.

Conclusion

The role of red blood cells is critical and significant in the diagnosis of several diseases and clinical conditions. Their structural appearance and functional ability alter in disease conditions. Basophilic stippling is one such promising biomarker in identifying hematological diseases, toxic exposures to heavy metals, and nutritional deficiency disorders.