--- HAEMATOLOGY AND BLOOD TRANSFUSION — NOTE 2 MBML 3223 Semester 3 Mount Kenya University Topic: Blood Transfusion Medicine --- SECTION 1: BLOOD GROUPS AND COM
--- HAEMATOLOGY AND BLOOD TRANSFUSION — NOTE 2 MBML 3223 Semester 3 Mount Kenya University Topic: Blood Transfusion Medicine --- SECTION 1: BLOOD GROUPS AND COMPATIBILITY TESTING The ABO Blood Group System The ABO system is the most important blood group system in transfusion medicine. ABO incompatibility causes the most severe and potentially fatal transfusion reactions. ABO antibodies are naturally occurring — they are present in the serum without prior exposure to foreign red cells. Blood Group Antigens on RBC Antibodies in Serum Can Donate RBCs To Can Receive RBCs From --- --- --- --- --- A A antigen Anti-B A, AB A, O B B antigen Anti-A B, AB B, O AB A and B None AB only All groups — Universal Recipient O None Anti-A and Anti-B All groups — Universal Donor O only - Universal RBC donor = O negative (no ABO antigens, no Rh D antigen) - Universal plasma donor = AB positive (no anti-A or anti-B antibodies in plasma) - Universal recipient = AB positive The Rh Blood Group System - The Rh system is the second most important blood group system after ABO - The most clinically significant antigen is the D antigen - Rh positive = D antigen present on RBC surface - Rh negative = D antigen absent from RBC surface - Rh-negative individuals do NOT naturally carry anti-D antibodies — they develop them only after exposure to Rh-positive blood, a process called sensitisation - Once sensitised, subsequent exposure to Rh-positive blood triggers a haemolytic reaction Haemolytic Disease of the Newborn (HDN): - An Rh-negative mother carries an Rh-positive fetus in the first pregnancy — usually uneventful - At delivery (or any sensitising event), fetal RBCs enter the maternal circulation - The mother's immune system recognises the D antigen as foreign and forms anti-D IgG antibodies — she is now sensitised - In a subsequent Rh-positive pregnancy, maternal anti-D IgG crosses the placenta - These antibodies attack fetal RBCs, causing haemolysis - Clinical consequences range from mild jaundice to severe anaemia, hydrops fetalis, and intrauterine death - Prevention: Anti-D immunoglobulin (Rhogam) is given to Rh-negative mothers within 72 hours of delivery, miscarriage, abortion, amniocentesis, or any other sensitising event, and also prophylactically at 28 weeks gestation. It neutralises any fetal RBCs before the mother can mount an immune response. Other Clinically Important Blood Group Systems After ABO and Rh, the most clinically relevant systems in order of importance are: Rank System Clinical Significance --- --- --- 3rd Kell Strong immunogen; causes HDN and haemolytic transfusion reactions 4th Duffy Duffy-null individuals are resistant to Plasmodium vivax malaria 5th Kidd Notorious for causing delayed haemolytic transfusion reactions 6th MNS Variable clinical significance --- SECTION 2: PRE-TRANSFUSION COMPATIBILITY TESTING Before any non-emergency transfusion, compatibility testing is performed to reduce the risk of transfusion reactions. Testing proceeds in three steps: - Step 1 — ABO and Rh Typing: The patient's blood group and Rh status are determined - Step 2 — Antibody Screen: The patient's serum is tested against a panel of reagent RBCs to detect unexpected or irregular antibodies that could react against donor blood - Step 3 — Crossmatch: The patient's serum is mixed directly with the chosen donor's RBCs. If no reaction occurs, the unit is compatible and safe to transfuse. If agglutination or haemolysis occurs, the unit is incompatible and must not be used. The crossmatch primarily detects irregular antibodies in the patient's serum that react against specific donor RBC antigens. Direct and Indirect Antiglobulin Tests (Coombs Tests) The antiglobulin test uses anti-human globulin (Coombs reagent) to detect antibodies either bound to RBCs in the body or free in the serum. Test What It Detects When Used --- --- --- Direct Antiglobulin Test (DAT) Antibodies already bound to the patient's own RBCs in vivo Haemolytic transfusion reactions; autoimmune haemolytic anaemia; HDN Indirect Antiglobulin Test (IAT) Free antibodies in the patient's serum in vitro Pre-transfusion antibody screening; crossmatching - A positive DAT means antibodies are actively coating the patient's own RBCs inside the body - The crossmatch is essentially a form of indirect antiglobulin testing Metabisulfite Test (Sickle Solubility Test) - Sodium metabisulfite is added to the patient's blood, creating a deoxygenating environment - Haemoglobin S becomes insoluble and causes RBCs to sickle - A positive result confirms the presence of HbS — either sickle cell trait (HbAS) or sickle cell disease (HbSS) - This test does NOT distinguish trait from disease — haemoglobin electrophoresis is needed for that --- SECTION 3: BLOOD PRODUCTS AND THEIR CLINICAL USE Whole blood is separated by centrifugation into its components: packed red blood cells, platelet concentrate, and plasma. Plasma is further processed into fresh frozen plasma and cryoprecipitate. 1. Packed Red Blood Cells (pRBCs) - Contains red cells with minimal residual plasma - Storage: 1–6°C for 35–42 days - Indications: symptomatic anaemia, acute haemorrhage, preoperative optimisation - In an emergency with unknown blood type: give O negative pRBCs 2. Fresh Frozen Plasma (FFP) - Contains all coagulation factors, fibrinogen, albumin, and immunoglobulins - Does NOT contain platelets - Storage: −18°C or below for up to 12 months - Indications: coagulation factor deficiency when specific concentrates are unavailable, liver disease with coagulopathy, urgent warfarin reversal, DIC, massive transfusion protocol, therapeutic plasma exchange in TTP - Universal plasma donor: AB positive FFP 3. Platelet Concentrate - Contains platelets suspended in a small volume of plasma - Storage: 20–24°C (room temperature) with continuous gentle agitation for 5 days - Has the shortest shelf life of all blood products - Has the highest risk of bacterial contamination because it is stored at room temperature - Indications: thrombocytopenia with active bleeding, prophylactic transfusion before procedures in severe thrombocytopenia 4. Cryoprecipitate Cryoprecipitate is prepared by slowly thawing FFP at 1–6°C and collecting the cold-insoluble precipitate that forms. It contains high concentrations of: - Fibrinogen (Factor I) — the most abundant component - Factor VIII - Factor XIII - Von Willebrand factor (vWF) - Fibronectin It does NOT contain significant amounts of Factor IX, Factor VII, or other coagulation factors. Indications: Haemophilia A when Factor VIII concentrate is unavailable, Von Willebrand disease, hypofibrinogenaemia, DIC (to replace fibrinogen), uraemic bleeding. 5. Albumin - Prepared from pooled plasma; does not transmit viruses (heat-treated) - Indications: hypoalbuminaemia, liver cirrhosis, burns, nephrotic syndrome, spontaneous bacterial peritonitis Storage Summary Blood Product Storage Temperature Shelf Life --- --- --- Packed RBCs 1–6°C 35–42 days Fresh Frozen Plasma −18°C or below 12 months Platelet Concentrate 20–24°C with agitation 5 days Cryoprecipitate −18°C or below 12 months Granulocytes 20–24°C 24 hours --- SECTION 4: TRANSFUSION REACTIONS Transfusion reactions are adverse responses to blood transfusion. They are classified by timing into immediate reactions (during or within 24 hours) and delayed reactions (days to weeks after transfusion). Immediate Transfusion Reactions 1. Acute Haemolytic Transfusion Reaction (AHR) - The most serious immediate transfusion reaction - Cause: ABO incompatibility — the most common underlying cause is a clerical error (wrong blood given to wrong patient) - Mechanism: recipient's preformed IgM antibodies bind to donor ABO antigens on transfused RBCs, activating the complement system, causing rapid intravascular haemolysis - Clinical features: fever, rigors, back and flank pain, haemoglobinuria (red or brown urine), haemoglobinaemia, hypotension, tachycardia, DIC, and acute renal failure - Management: stop the