Haematology

Obtaining blood

For haematologic exercises venous blood obtained form a vein is better. However, for total and differential counts and haemoglobin estimation blood can be taken by pricking:

The lobe of the ear: The surfaces of the tip of the finger; in infant, from the plantar surface of heel, or the great toe. The puncture should be about 3mm deep. An edematous or a congested part should not be punctured. If the area to be punctured is cold and xyanotic, warm it by massaging or else erroneous results may be obtained. Clean the site with spirit or alcohol, let dry and puncture. Wipe off the first drop of blood never attempt squeezing out of blood. Having obtained the requisite amount of blood let the patient apply slight pressure over the area with a sterile swab.

Usually superficial veins of the upper extremity are used. Inspect the veins, use a tourniquet if needed. Use a sytinge of a size according to the amount of blood required. Needles of gauge 21 or less should be used and be 1 to ½ inches long. Instead of a tourniquet one can use a sphygmomanometer cuff, apply pressure that is midway between systolic and diastolic pressure. Ask the patient to open and close his firs several times. Take aseptic precautions and puncture the skin and then the vein the bevel of the needle should be facing upwards. Various veins that can be used are given in diagram. Sometimes it may be difficult to obtain blood at the first instance, withdraw the needle and in many instances blood will flow back into the syringe. Having withdrawn blood, loosen the tourniquet and ask the parent to open his fist. Let the patient apply a sterile gauge piece with gentle pressure over the area. Make sure that the bleeding has stopped before the patient leaves. In infants blood may be secured form femoral or external jugular vein. Transfer blood from syringe into the appropriate container gently.

This acts by chelating calcium and preserves cellular elements better than does oxalate. It is used for blood counts, ESR and PCV estimations. Smears can be made up to 3 hours after sample collection. EDTA prevents platelet adhesion and aggregations, hence, it is best for platelet counts too.

Used for ESR and haematocrit Potassium and ammonium oxalate salts are uses together in 2:3 ratio respectively. While potassium oxalate causes cell shrinkage, ammonium oxalate counter acts and the cell size and shape is maintained. Oxalates act by oxalate can not be used for this purpose.