Blood Sampling PDF

BLOOD SAMPLING Dr. Neven Makram Aziz  Blood Blood is the vital fluid tissue that circulates inside blood vessels. It represents 8% of body weight (5.6 L).  Functions of blood:  Transport function.  Defensive function.  Hemostatic function (stoppage of bleeding).  Ho...

BLOOD SAMPLING Dr. Neven Makram Aziz  Blood Blood is the vital fluid tissue that circulates inside blood vessels. It represents 8% of body weight (5.6 L).  Functions of blood:  Transport function.  Defensive function.  Hemostatic function (stoppage of bleeding).  Homeostatic function. Composition of blood  Plasma proteins Type Concentra Function Site of formation tion Albumin 4 gm/100 - Osmotic pressure due to its Liver. ml plasma highest concentration. - Transport of some substances. Globulin 2.5 - Defensive function (γ Reticuloendothelial (α, β, γ) gm/100 ml globulins). system (R.E.S) in plasma - Transport of some liver, spleen, lymph substances. nodes and bone marrow. Fibrinogen 0.4 - Blood clotting. Liver. gm/100 ml - Blood viscosity (Elongated plasma shape). Prothrombin 10 mg/100 - Blood clotting. Liver. ml plasma  Red blood corpuscles (R.B.Cs): 5 million per cubic mm. Their decrease is called anemia and their increase is called polycythemia.  White blood corpuscles (W.B.Cs): 4000-11000 per cubic mm. Their decrease is called leucopenia and their increase is called leucocytosis.  Platelets: 250000 to 500000 per cubic mm. Their decrease is called thrombocytopenia and their increase is called thrombocytosis. Blood vessels  Arteries Veins 1- Blood vessels that transport blood 1- Blood vessels that transport blood to the away from the heart. heart for oxygenation. 2-Usually positioned deeper within the 2- Usually positioned closer or beneath the body. surface of the skin. 3- Arteries have a thick walls and a 3- Veins have a thinner walls and a wider narrow lumens. lumens → so can store blood. 4- Arteries are eight times less distensible 4- Veins are the most distensible → a slight (change in volume/change in pressure) increase in the pressure allow veins to because of the stronger walls. accommodate 0.5 to 1 liters of blood so we give blood and fluid intravenous injection.  Types of blood samples: 1- Venous sample (preferred method for clinical tests): Method of Collection; - Direct puncture of superficial vein by venipuncture (needle). (In infants, venous blood may have to be taken from the femoral vein, or the frontal venous sinus). Common Use; - Routine laboratory tests (for complete hematological and biochemical investigations). 2- Arterial sample: Method of Collection; - Direct puncture of artery (Radial or Femoral) by a needle. Common Use; - Arterial blood gases - Blood pH 2- Capillary sample: Method of Collection; - Dermal puncture of fingertip or heel. (In adults and older children, capillary blood is generally obtained from a skin puncture made on the tip of the middle or ring finger, or on the lobe of the ear. In infants and young children in whom the fingers are too small for a prick, the medial or lateral side of the pad of the big toe or heel is used). Common Use; - For estimation of Hb, cell counts, bleeding time and coagulation time, blood films, micro chemical tests but these values are likely to be on the lower side since some tissue fluid is bound to dilute the blood even when it is free-flowing. - For detection of blood groups. - It is used for Infants and young children, Elderly patients with fragile veins and severely burned patients. - There is greater risk of contamination Two types of blood samples are not suitable for hematological tests: 1. Clotted samples: Even little clots in the anti-coagulated blood can negate the results. 2. Hemolysed samples: The red cells may be damaged and ruptured during collection or handling of blood. The released Hb tinges the plasma or serum red, rendering the sample unfit for tests. For a Sample of Whole Blood or Plasma (Plasma = Blood minus all the blood cells): 1- Draw blood from a vein as described below and transfer it from the syringe to a container containing a suitable anticoagulant. 2- Mix the contents well (without foaming). 3- A sample of whole blood is now ready for tests. If plasma is desired, centrifuge the anti-coagulated blood for 20–30 minutes at 2500 rpm (revolution per minute). 4- Collect the supernatant plasma with a pipette and transfer it to another container. (The packed RBCs will be left behind)  For a Sample of Serum (Serum = Plasma minus fibrinogen and all the clotting factors): 1- Transfer the blood from the syringe to a container without any anticoagulant in it. 2- After the blood has clotted in an hour or two and the clot shrunk in size, the serum will be expressed. 3- Remove the supernatant serum with a pipette and transfer it to a centrifuge tube. 4- Centrifuge it to remove whatever red cells may be present. Clear serum can now be collected with another pipette.