Red Blood Cell Disorders

Haematology: RBC Disorders and Clinical Haematology

• This presentation covers red blood cell (RBC) disorders and clinical haematology.
• Dr G O'Connor, [email protected], is the presenter.

Red Blood Cells

• RBCs are designed to carry oxygen from the lungs to body tissues.
• Their cytoplasm contains haemoglobin, an oxygen-binding protein.
• Their small diameter (7–8 µm) and biconcave shape maximize surface-to-volume ratio, aiding oxygen exchange.
• The diameter of a RBC is 7.2 µm.

Haemoglobin

• Adult haemoglobin is a tetramer of 2β₂.
• Each chain carries an iron-containing haem group.
• Haemoglobin reversibly binds oxygen to form oxyhaemoglobin.
• Oxygen binding to one haem group increases oxygen affinity for other sites (cooperative binding).

Measuring Haematological Parameters

• Full blood count (FBC) assesses various RBC characteristics.
• Parameters include red blood cell count, mean cell volume, packed cell volume, haemoglobin, mean cell haemoglobin, mean cell haemoglobin concentration, and red cell distribution width.

Blood Film

• Blood films are stained microscopic examinations of blood samples, displaying various blood cell types, including RBCs.
• Typical blood film images are provided in the presentation.
• Different blood cells (e.g., platelets, lymphocytes, monocytes, eosinophils, neutrophils, basophils) are identifiable on the smear.

Red Blood Cell Disorders

• Anaemia is the most prevalent blood disorder globally.
• Anaemia results from reduced red blood cell haemoglobin concentration.
• Symptoms can range from mild (asymptomatic) to severe, reflecting reduced oxygen delivery.
• Common symptoms include fatigue, lethargy, breathlessness, fainting, pallor, palpitations, worsening angina, loss of appetite, and weight loss.
• Assessing the lower eyelid conjunctiva (appears pale pink or white in anaemia) helps diagnose anaemia.

Basis for Classification of Anaemia

• Categorization is primarily based on RBC size and shape.
• Microcytic anaemia involves small RBCs, while macrocytic anaemia involves large RBCs.
• Poikilocytosis (nonuniform cell shapes) and anisocytosis (nonuniform cell sizes) further aid in classifying erythrocyte disorders.
• Based on cell morphology, different types of anaemia (e.g., microcytic, macrocytic, normocytic) are diagnosed.

Acquired or Inherited Anaemia

• Anaemia arises due to significant blood loss, reduced red cell production, or excessive red cell destruction.
• Acquired causes include iron, vitamin B12, or folate deficiency, blood loss, chronic disease, immune reactions, bone marrow infiltration (e.g., leukemia, lymphoma), and aplastic anaemia.
• Inherited causes include haemoglobinopathies (e.g., thalassemia, sickle cell disease), red blood cell membrane defects, and red blood cell enzyme defects.

Anaemia: RBC MCV

• MCV (<80 fL) represents microcytic anaemia (small red blood cells).
• MCV (> 96 fL) represents macrocytic anaemia (large red blood cells).
• Normal MCV represents normocytic anaemia (normal-sized red blood cells).

Reticulocyte Count

• Reticulocyte count helps evaluate red blood cell production.
• Elevated reticulocyte counts indicate increased red blood cell production in response to conditions like haemorrhage or haemolysis.
• Decreased reticulocyte count suggests a problem in red blood cell production.

Microcytic Anaemia: Iron Deficiency Anaemia

• Iron deficiency anaemia is a common cause of microcytic anaemia.
• Low iron levels result in reduced haemoglobin synthesis.
• Symptoms include typical anaemia symptoms; further symptoms involving mucous membranes, nails, and mouth are more specific to this type of anaemia.

Causes of Iron Deficiency

• Insufficient iron intake (poor diet).
• Increased iron requirements (growth spurts, pregnancy).
• Malabsorption (gastrointestinal issues).

Laboratory Findings of Iron Deficiency Anaemia

• Low haemoglobin, low MCV, low mean corpuscular haemoglobin.
• Blood film shows microcytic, hypochromic cells, pencil cells, and target cells.

Biochemistry of Iron Deficiency Anaemia

• Serum iron, transferrin, and total iron-binding capacity (TIBC) are examined.
• Serum ferritin is often reduced in iron deficiency.
• Reduced serum ferritin and elevated TIBC directly suggest low iron levels, with accompanying inflammation potentially masking this result.

Latent Iron Deficiency

• Latent iron deficiency involves reduced storage iron before overt anaemia.

RBC Antigens

• Transfusion of red blood cells requires compatibility between donor and recipient.
• ABO blood group antigens and Rhesus D antigen are critical.

ABO Blood Groups

• ABO blood group antigens are carbohydrates.
• Individuals possess antibodies against antigens they don't have (Landsteiner's rule).
• ABO incompatibility can cause serious reactions during transfusions.

Rhesus Grouping

• Five primary Rh antigens — D, C, c, E, and e — exist.
• D is the most significant for clinical purposes.
• Anti-D antibodies arise from previous exposures or incompatibility and can cause complications.
• Rhesus incompatibility can result in haemolytic disease in the newborn.

Haemolytic Anaemia

• Increased red blood cell destruction characterizes immune haemolytic anaemia.
• Underlying causes include autoantibodies or complement attacking red blood cells.
• A variety of medications, such as penicillin, quinidine, and methyldopa, can induce drug-induced haemolytic anaemia.

Other Considerations

• Reduced erythropoietin (EPO) production due to renal disease or bone marrow failure can lead to anaemia.
• Myelodysplastic syndromes (MDS) lead to immature blood cells failing to develop fully.

Blood Products

• Individual blood components are generally preferred over whole blood.
• Processing removes white blood cells (leukodepletion) to minimize immune reactions.

Blood Component Uses

• Red blood cells treat hypovolemia and severe anaemia.
• Fresh frozen plasma provides coagulation proteins.
• Cryoprecipitate contains high fibrinogen levels and is used for disseminated intravascular coagulation (DIC) or specific fibrinogen deficiency.
• Platelets treat bleeding related to thrombocytopenia.

Transfusion Reactions

• Various adverse reactions can occur during transfusions, including acute haemolytic reactions, febrile non-haemolytic reactions, allergic reactions (sometimes with anaphylaxis), and transfusion-related acute lung injury (TRALI).
• Delayed reactions such as delayed haemolytic reactions, graft-versus-host disease, and post-transfusion purpura are also potential complications.
• Infections like bacterial, viral (hepatitis B, C, and HIV), and prion diseases are possible but rare risks.