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 Anticoagulation Whole blood A venous, arterial or capillary blood sample in which the concentrations and properties of cellular and extra-cellular constituents remain relatively unaltered when compared with their in-vivo state.  Anticoagulation in-vitro stabilizes the constituents in a whole blood sample for a certain period of time. Plasma  The virtually cell-free supernatant of blood containing anticoagulant obtained after centrifugation. Serum  The undiluted, extracellular portion of blood after adequate coagulation is complete. CLOTTING MECHANISM ANTICOAGULANTS Anticoagulants prevent blood from clotting. They are added to the blood sample, especially  when blood is collected by venipuncture, and sent to the laboratories for investigation. They are additives that inhibit blood and/or plasma from clotting (ensuring that the constituent to be measured is non-significantly changed prior to the analytical process).  Anticoagulation occurs by binding calcium...

Collection of blood INTRODUCTION  Blood is one of the most common specimens used in laboratory determinations.  Venous blood is preferred for most hematological examinations.  Peripheral samples (capillary blood) can be used satisfactorily for many purposes if a free flow  of blood is obtained, but this procedure should be avoided in patients who may be possible carriers of transmissible diseases.   Capillary blood is used commonly for hemoglobin estimation, cell counts, blood grouping,  bleeding and clotting time determination, and other investigations that use less blood, whereas  venous blood is preferred for a comprehensive hematological investigation. What are Arteries? Arteries are blood vessels that carry blood from the heart to the entire body. The blood is ‘mostly’  oxygenated in arteries. Arteries are also responsible for carrying nutrients to the cells. Two exceptions where arteries carry deoxygenated blood. i. Pulmonary artery whe...

 Type II: Antibody Dependent Cytotoxic Hypersensitivity  • Type II hypersensitivity is an allergic reaction due to the interaction of antibodies and cell associated antigens.   • When antibodies bind to the antigens located on the surface o cells, the cells become cytotoxic. Hence the name cytotoxic reaction  In type II hypersensitivity IgG type antibodies are involved.   Eg. Agglutination and lysis of blood cells due to mismatched blood group,. transfusion. Erythroblastosis foatalis, Autoimmune hemolytic anemia, etc.   • Based upon the type of antigen involved in the reaction, cytotox hypersensitivity is classified into two types, namely:  Isoimmune reactions  Transfusion reactions Erythroblastosis foatalis Transplant rejection reactions.  Autoimmune reactions are:  Autoimmune hemolytic anemia  Autoimmune thrombocytopaenic purpusa  Autoimmune thyroiditisA utoimmune glomerulonephritis. Mysthenia gravis. • In...

 II.  Classification Based on the Different Mechanisms of Pathogenesis Coombs and Gell (1963) proposed 5 types of hypersensitivity based on the different mechanisms of pathogenesis.  They are the following::  1. Type I : Anaphylactic hypersensitivity.  2. Type II  : Antibody - dependent cytotoxic hypersensitivity.   3.Type III  : Immune complex - mediated 'hypersen sitivity.   4. Type IV:  Cell - mediated hypersensitivity.   5. Type V:  Stimulatory hypersensitivity.   Of these 5 types, type IV alone is delayed type of hypersensitivity and the other types are immediate type.   Type I: Anaphylactic Hypersensitivity  (Anaphylaxis)  Anaphylaxis is defined as an allergic reaction to an foreign substance to a foreign substance to which it has previously become sensitized resulting from the release of histamine, serotonin and other vasoactive substances.   The term anaphylaxis was...

 Types of Hypersensitivity  Hypersensitivity is classified in two ways. They are:  1. Based on the time taken for the reaction  2. Based on the different mechanisms of pathogenesis.   I. Classification Based on the Time Taken for Reactions  Based on the time required for a sensitized host to develop clinical reactions upon reexposure to the antigen, hypersensitivity is classified into two categories They are:  1. Immediate hypersensitivity  2. Delayed hypersensitivity.   1. Immediate Hypersensitivity  When the immune reactions manifest in a short duration of time, within minutes, the hypersensitivity is called immediate type. Most of the hypersensitivity to drugs like penicillin belong to this category. Hay fever is another example. Immediate hypersensitivity is characterized by the following salient features:  1. This immune reaction appears and disappears rapidly. 2. Inflammatory response occurs in a few minutes....

 Hypersensitivity  Hypersensitivity simply means allergy.  It is defined as the violent reaction of the immune system leading to severe symptoms and even death in a sensitized animal when it is re - exposed to the same antigen for the second time.  The factors causing hypersensitivity are called allergens.  In clinical terms, hypersensitivity is called allergy.  A familiar example for hypersensitivity is the allergy caused by penicillin injection.  Sometimes, in hospitals a patient dies immediately after penicillin injection.  This is due to allergy.  The allergy caused by drugs is called drug allergy.  The immune system is devised by nature primarily to protect the human body against pathogens.  Sometimes this system becomes overenthusiastic, and brings discomfort.  This phenomenon is similar to the overenthusiastic servant who tried to kill the fly sitting on the king's nose with a strong sharp knife.  Immune response is...