Blood specimens may be collected from:
Venous blood: This is used generally except for the estimation of pH, p02 and PCO2. which require arterial blood,
Arterial blood: For the estimation of pH. po, and pco2 the specimen is collected in a heparinised syringe. It is freed from air bubbles and capped. The blood is sent immediately on ice to the laboratory.
Capillary blood: This is mixed venous and arterial blood. It is collected from heel-pricks, finger or the ear lobe using a stylet pin when only a small quantity of blood is needed.
Blood may be collected with anticoagulants. When the blood is separated either by allowing it to stand undisturbed or by centrifugation, the supernatant is knorvn as plasma. Plasma contains fibrinogen and clothing factors. The type of anticoagulant used depends on it effect on the test to be carried out. The amount of anticoagulant needed is usually just enough to prevent the blood from clothing without alteration to the cell and plasma constituents.
care must therefore be taken not to exceed or fall below the stated mark on the’ container for the amount of blood required.
Some anticoagulants in common use are:
1. Haparin : (usually the lithium salt) it is suitable for all biochemical estimation: it prevent the coagulation of blood by
2. Ethylene Diamine fetra acetic acid (Selquestrine): Its action is to chelate calcium(factor v) from solution so that it is not available in the clothing system to affect blood clothing, It is used mainlly for estimations in haematology.
3. Oxalates: (The Sodium, Ammonium or Potassium salt):it also precipitate out calcium from solution
Anticoagulant Floride: glucose bottle (yellow cover), glucose presavatives, it preventenolase glycolytic pathoning for glucose analysis.
Fluoride: inhibits enolase in the glycolytic cycle and thus prevents the red cells from using up the glucose in the solution while the specimen is waiting for analysis. It is sometimes used in combination with oxalate for specimens collected for the determination of blood glucose.
Blood collected without an anticoagulant is allowed to clot. The clot retracts and it is separated to obtain serum. Serum does not contain fibrinogen and the other clotting factors. Usually blood is obtained without tourniquet. Tourniquet causes stasis and affects the result of some measurements in the blood. If the vein is difficult to find however the tourniquet may be used but it is released once the blood has started to flow.
The blood obtained is mixed gently; the container is correctly labeled and sent to the laboratory without delay.
The specimen must be accompanied with:
1. A proper identification of the subject
2. The location of the subject
3. details of the tests requested
4. The name of the requester to be contacted in case of an emergency result.
Preparation of subjects for blood-taking:
The subject should be seated comfortably and measured, An arm rest may be needed to steady the arm
. The relevant containers
. The right volume of disposable syringe
. A needle with the correct bore to facilitate easy flow of blood swabs dry and with methyllated spirit or tourniquet if required.
Identify the vein to be used with or without the use of a tourniquet. Be careful not to use the arm into which a drip is running.
Swab the vein, release the air in the syringe. if any . Carefully insert the needle into the vein. and draw out the blood.
At the end of the venepuncture. apply pressure to the puncture site using a dry swab.
Make sure that the bleeding has stopped before releasing the subject. In order to avoid haemolysis. do not squat the blood through the needle into the appropriate container. Remove the needle and gently, deliver the blood.
In the laboratory, clotted blood is allowed to stand for 20 minutes.The serum/plasma is separated by centrifugation at 30009 for 15 minutes in a closed container unless whole blood is to be used. The specimen is analysed immediately or stored under appropriate conditions until analvsed.