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 Having withdrawn blood, loosen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.