Blood Groups
DIFFERENT BLOOD GROUPS
ABO system The membrane of RBCs contain antigens of two types (A) and (B) Characters of these antigens are : - inherited according to Mendelian law - appear in fetal life and persist throughout life. - specific reaction with the corresponding antibodies In the plasma there are antibodies against A and against B and they also are inherited.
According to the types of antigens and antibodies, the blood groups are classified into: % Antibodies Antigens Gro- up 41% Anti-B A 9% Anti-A B 3% - A & B AB 47% Anti A & B
universal recipients universal donors
Importance of blood groups (1) Medicolegal importance: In disputed paternity (good negative test). In the criminal practice. (2) Blood transfusion The recipient’s plasma should not contain antibodies against the donor’s red cells
Incompatible blood transfusion The donor’s RBCs are agglutinated by recipient plasma The donor’s serum are diluted by recipient blood so its antibodies are with less or no effect on the recipient RBCs
RHESUS MONKEYS
Rhesus factor (Rh-factor) People are divided according to the presence or absence of Rh- antigen (agglutinogen) on RBCs membrane into: Rh +ve (have D- antigen) = 85% Rh –ve (without D- antigen) =15%.
1- They are normally absent Rh-antibodies They differ from ABO antibodies in: 1- They are normally absent but induced by blood transfusion of Rh positive blood to Rh-negative patient or in pregnancy.
2- Rh-antibodies are IgG but ABO-antibodies are IgM . - IgM has large molecules and can’t cross placenta - IgG has small molecules and can cross placenta.
Importance of Rh-factor A- Erythroblastosis fetalis Rh +ve male + Rh –ve female Rh +ve fetus Rh +ve fetal RBCs enter the circulation of the mother and sensitize her liver to produce anti- D antibodies (agglutinins).
- Antibodies (IgG) cross the placenta to the Rh +ve 2nd fetus - The 2nd or 3rd fetus is born anaemic, jaundiced or born dead - The 1st baby is also affected if the mother is sensitized by previous transfusion of Rh +ve blood.
Prevention: 1- Rh –ve female should never receive Rh +ve blood 2- Anti-D antibodies are given to the mother during 48 hours after each delivery to neutralize the D-antigen of fetal RBCs transmitted to her prevent formation of liver antibodies Treatment: Gradual replacement of baby’s blood with Rh –ve group O (exchange blood transfusion).
B- Repeated blood transfusion: If Rh –ve person is transfused with Rh +ve blood he will produce antibodies against Rh-factor if this person retransfused with Rh + ve blood agglutination
Determination of blood group: 1- By slide technique
2- By cross matching between recipient and donor blood Group A + Group B = Clumping of RBCs +
Blood Transfusion The reason for a progressive blood sampling strategy by FIS should be considered in the light of the Lahti CC Worlds in 2001 where six Finnish team members including the team doctor and head coaches admitted to more or less organised doping including the easy to discover masking agent, HES. A substantial blood testing programmes was initiated by FIS at the beginning of 2001-2002 season including pre competition Full Field testing, Post Competition testing and OOC target testing. IDTM was responsible for the collection of the samples and of the out sourcing of the laboratory work that some of the samples needs to undergo.
Indications: 1) Decrease blood volume (haemorrhage more than 30%). 2) In severe anaemia (Hb is less than 7gm/dl). 3) Restore blood contents as platelets, packed RBCs or clotting factor as in purpura and hemophilia 4) Erythroblastosis fetalis by exchange transfusion.
Precautions 1) Blood is obtained from healthy donors - Age =18-60 year - Weight: more than 55 kgm - Blood pressure within normal range - Hb% is not less than 90% (13gm/dl). - Haematocrit value at least 40%. - Free from infectious diseases as AIDS, viral hepatitis
2) Blood used is stored at 4C not more than 21 days 3) Blood bag must contain, sodium citrate (anti-coagulant), citric acid (reduce pH) and dextrose (nutrient of RBCs) . 4) Blood groups are compatible by double cross matching test 5) The blood is warmed before transfusion to restore the Na-K pump
Complications of blood transfusion A- Incompatibility which leads to: 1. RBCs are agglutinated in clumps block small blood vessels pain in chest and back 2. Agglutinated RBCs hemolyse and hemoglobin is liberated in plasma and Converted to bilirubin post-transfusion jaundice and precipitated in renal tubules blocking it renal failure .
B- Other complications 1-Transmission of diseases as AIDS & hepatitis B,C. 2- Excessive transfusion heart failure. 3- Hyperkalemia arrhythmia 4- Hypocalcemia tetany 5- Allergic reactions
Changes occur in stored blood 1- Increase K+ ions in plasma (Na-K pump inhibited by cold) . 2- Decrease dextrose and changed to lactic acid. 3- Decrease Platelets number . 4- RBCs swell and become spherical. 5- Decrease clotting factors VII, VIII , IX 6- Decrease 2,3 DPG less O2 supply to the patient hypoxia.