In case of blood specimen, specimen container used for blood for biochemical investigation must be leak proof and chemically clean. Syringe and needle for collecting the blood sample must also be chemically clean, dry and sterile.
Venipuncture is the accepted method of blood collection. Some factors that affect the correctness of test result Do originate from blood collection this factors include:
Factor that affect correctness of laboratory result
1. Wrong venipuncture techniques
2. Hemolysis of red blood cells
3. Use of wrong container
4. Instability of some substance in the blood.
The use of disposable needle and syringe minimise the risk of infections due to serum hepatitis virus and human immunodeficiency virus (HIV).
For the same reasons plastic tube and bottles are prefer to glass ones.
It is easier to enter a vein which can be files than the one that is only seeing.
The technique should not be applied too tightly nor too long in order not to cause venous stasis which can lead to concentrations of certain substance such as hemoglobin, plasma proteins and calcium.
It is wrong to collect blood for chemical analysis from the arm into which an intravenous infusion is already being given.
Hemolysis of red blood cell
Red blood cell are not often used for biochemical investigation as a rupture of the red blood cells can lead to unreliable results. This is because herbal essence course substance from the cell to be released into the serum or plasma thereby giving a false increase in the concentrations of the substance being tested. To avoid hemolysis
Use good clean sterile and dry syringe and needle
Withdraw blood slowly and steadily.
Allow sufficient time for the blood to clot and retractions of the clot to occur.
Avoid prolonged centrifuging in 3 to 5 minutes at 700g is adequate.
Do not shake blood sample, instead mix gently if the container contain anticoagulant.
Do not freeze whole blood sample.
Most by chemical analysis requires serum. Blood is there for collected in to dry, clean the containers.
There are some tests, however, that require plasma. Top obtain plasma, anticoagulant I use to prevent clotting. Whenever possible, using plasma instead of serum is more advantageous because the yield of plasma from a given volume of blood is greater, and the test can be performed immediately. Lithium heparin is the most ideal anticoagulant as it does not affect chemical reaction, it helps to reduce the action of hemolysis and lack sodium or potassium salt which may interfere when electrolytes are to be measured. But due to the eat high-cost, other anticoagulant such as EDTA (ethylenediaminetetraacetic acid) and fluoride oxalate are widely used and even thought they contain sodium and potassium salts.
Fluoride is an enzyme inhibitor which prevents glycolysis (broken down of glucose to lactic acid by enzyme action) therefore, it must not be used where enzyme activity is to be estimated.
Preservations of blood
Chemical substance in blood are present in both plasma and cell in varying quantities. Prom separations of plasma or serum from cell is important in order to prevent chemical change which cannot call in whole blood. Refrigerations or blood specimen period to separations of plasma can lead to false high potassium level. Glycolysis cannot call if fluoride oxalate anticoagulant is not use. Bilirubin will be decomposed on prolonged exposure to light. It is important to refrigerate serum or plasma at 4 degree Celsius or freeze at – 20 degrees Celsius until analyse. As much as possible, blood specimen should be handled aseptically to prevent and minimise chance of bacterial contamination
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