In the below contents we will study about phlebotomy techniques both by syringe methods and capillary method.
Phlebotomy Technique by Syringe Methods:
Sterilized sharp needles of bore size 18-20 gauge (medium, 12-0.9 mm) for adults and 23 gauge (0.5 mm) for children are needed. The bevel length should be medium (20 mm) for adults and short (15 mm) for children. The use of disposable needles in recommended.
Syringes of different capacities, 2-, 5, 10- and 20-mL, should be available. The size of the syringe to be use depends on the amount of blood needed.
Procedure of Venipuncture:
The procedure of venipuncture comprises of three steps- preparation, drawing blood and cleanup.
i. Introduce yourself to the patent and be pleasant. Read the patient’s request from carefully. Identify the patient by name, date of birth and accession number. If the patient should be fasting before giving blood, inquire if the patient has done so.
ii. Decide how much of blood is needed and arrange the correct tubes (s) to be used for each test. For example, if hierogram is requested 2mL of blood in EDTA-tube will be sufficient, whereas, if the blood is needed in the biochemistry laboratory, 10 mL of blood in a plain container without any anticoagulant would be needed. This will yield the required amount of serum.
iii. Plain the sequence in which blood for a coagulation assay. So, collect this in the second tube, which will be used for other tests.
iv. Fix the needle on to the syringe, touching only the top of the needle. Test the needle and syringe to make sure that the needle is not blocked and the syringe is airtight. Place the end of the needle in the sterile tube until ready for use.
v. Ask the patient to sit alongside the table used for taking blood. The patient should sit on a chair so that he/she can comfortably stretch horizontally the left or right arm. It also applies to a patient in the horizontal position (in bed). The elbow may be supported by an armrest.
vi. Fix the needle on to the syringe, touching only the top (syringe end) of the needle. Test the needle and syringe to make sure that the needle is not blocked and the syringe is airtight. Place the end of the needle in the sterile tube until ready for use.
i. Apply the tourniquet
(a) Place the tourniquet under the patient’s arm just above the bend in the elbow. With the right hand, warp the tourniquet firmly around the arm and hold the ends.
(b) With the left hand, pull one of the torniquet’s ends across.
(c) Loop the end under the main part of the tourniquet half way through in a slipknot. The tourniquet should be just tight enough to slow down flow and distend the veins; however, it must not be so tight that the blood flow in the arteries is reduced. The slipknot can be easily released when the tourniquet is to be removed.
(d) Ask the patient to open and close his or her hand several times to swell the veins. Using the index finger of your left hand fell for the vein where you will introduce the needle. Palpate the filled vein about 5-7 cm distal from the tourniquet and identify the site for vein puncture.
(e) Disinfect the site on the skin with a sterile gauze or cotton swab soaked with 70% alcohol.
(f) Take the syringe in your right hand, holding your index finger against the top of the needle.
(g) Position the needle with the bevel uppermost and hold it at a low angle (about 150- 250) to the skin vein without hesitation in the direction of the anatomical course of the vein to avoid injury to the interior wall of the vessel, which would cause pain to the patient.
Never approach a vein form the side:
i. You will feel the needle going through- the layer of skin, which is resistant, than the wall of the vein, which is less resistant (more flexible). So there will be a sudden loss of resistance as you penetrate the needle. Push the needle along the line of the vin to a depth of 1.0-1.5 cm.
ii. With your left hand pull back the piston of the syringe slowly.
iii. Continue to withdraw the piston to fill the syringe with the required amount of blood
iv. After the requisite amount of blood is withdraw, place a sterile dry gauze pad under the needle still sticking in the vein.
v. Open the tourniquet, by pulling the looped end and allow blood to flow freely in the vein. Do not pull the syringe and needle out prior to opening the tourniquet.
vi. Apply a dry swab over the hidden point of the needle. Withdraw the needle in open rapid movement from under the swab
vii. Ask the patient to press firmly on the cotton wool swab for 3 min, keeping the arm outstretched. Bending the arm back over the swab is not recommended because of the risk of a haematoma.
viii. Remove the needle from the syringe.
(a) Expel the blood slowly out the syringe gently down the side of the container tube or vial. Fill specimen tubes or vials with the blood up to mark. Immediately invert tubes of vials that contain the anticoagulant several times to ensure complete mixing of anticoagulants.
For the measurement of certain analytes, it should be ascertained that the patient has fasted for 12 h. Inquire from the patient is he/she followed the physician’s instructions.
Preventing Haematoma during Venipuncture:
i. Preferably use veins in the elbow area an only major veins.
ii. Be careful that the bevel of the needle is fully inside the vein.
iii. Be careful not to transverse the vein.
iv. Loosen the tourniquet and ensure homeostasis with a dry sterile cotton ball before pulling out the needle.
i. When patients are receiving a transfusion or infusion, blood should never be collected near the infusion site or from the catheter but from the opposite arm. If neither arm is free, an ankle vain is the site of choice for the venipuncture. The rationale for this is to avoid collecting any substance that has been infused (e.g. glucose, potassium gentamicin and heparin) and which could give rise to misleading interpretation of results.
ii. In the weak or elderly patients, the venous pressure may be so low that the pressure of the needle may collapse the vein. Take extra care to draw the blood slowly.
iii. If the patient’s clothing is too tight above the venipuncture site, it slows down the flow of blood and it may also cause haematoma. Loosen the cloth before drawing blood.
Phlebotomy Technique by Capillary Method:
A capillary is a small blood vessel connecting the small arteries (arterioles) to the small veins (venules). The capillary blood is obtained by skin puncture. It provides only small quantities of blood specimens from making a blood smear or haematocrit determination.
Skin puncture specimen is preferred over venipuncture specimen for the microscopic study of a blood smear avoiding the patient’s traumatic experience during venipuncture. It, however, yields only a small amount of specimen, which is inadequate for most routine tests.
Capillary blood samples are more difficult to handle than venous blood samples and should only be used in special circumstance, e.g. neonates and infants, control check for diabetes, severe anaemic patients, and blood gas analysis and in certain patients in whom venous blood sampling is difficult.
Squeezing of the finger and subsequent dilution with interstitial fluid is the major reason for errors in capillary sampling, .e.g. a decrease of concentrations of component and particulate matter (e.g. blood cells and parasites) and haemolysis.
To reduce this, remove the first drop of blood before collecting the sample with a free flow of blood. Capillary blood is also used for preparing thin and thick blood films for the diagnosis of malaria and other blood parasites (Borrelia, trypanosomes, and microfilariae)
Site for Capillary Blood Collection (Fig. 11.3):
i. Ear-lobes in adults and children
ii. Fingertips in adults and children
Finger punctures should not be performed in infants, as there is a risk of inuring the bone. Puncturing the planter surfaces of the hell of small infants can also damage the heel bone.
i. Big toe and medial and lateral position of the planter surface of the foot of neonate.
i. Cotton ball and sterile gauze pad.
ii. Capillary tubes (may be coated with heparin to avoid blood clotting prior to the investigation).
iii. Disinfectant (ethanol or isopropanol, 70%)
iv. Lancet or needle, sterile
Procedure (Fig. 11.4):
1. Check the things you need. Allow the patient to sit comfortably.
2. Find a spot on the middle finger or ring finger of the left hand. The spot is located on the side of the finger, which is less sensitive than the tip. Toe puncture and ear lobe puncture are done in case of infants. Avoid previously punctured sites.
3. Increase the blood flow by rubbing or carefully warming the skin in order to enhance the accumulation of capillary blood similar in composition to that of arterial blood. Use of warm water may be advisable for elderly patients. Cold skin might prevent a free flow of blood which is essential.
4. Cleanse the puncture site with a sterile gauze pad soaked with 70% alcohol.
5. Dry the puncture site with a sterile gauze pad (or air dry), so that residual alcohol will not mix without flowing blood; otherwise haemolysis may occur. Wet puncture site also does not allow the oozing out blood to form into a well-rounded drop, which is necessary for good result especially when the drop is used for smearing on the slide.
6. Grab the finger firmly and quickly puncture the site with a sterile lancet. The puncture should be 2-3 min deep.
7. Wipe away the first drip of blood with dry sterile cotton wool or gauze. The first drop of blood if, contaminated with tissue fluid and will interfere with the laboratory results if used. The succeeding drops are used for laboratory test.
8. Collect the out flowing blood in a capillary tube by holding the tube to the blood drop. This will be used for the haematocrit determination or sucking into the Sahli’s pipette for haemoglobin determination or for blood count. By touching the blood drop on a clean slide, smear can be made on the site. About 20ml. of blood will probability be needed in completing laboratory requirements?
9. After blood collection, press the puncture site with a dry sterile gauze pad to stop further bleeding.
Things to Remember:
i. To avoid infection do not puncture the same site twice.
ii. Never touch the tip of a sterile blade or keep it on the table. If a disposable lancet is not available, you can use broken glass chips sterilized in alcohol.
iii. Do not touch the blood; use rubber gives, if available. All specimens are potentially hazardous. Hepatitis B virus and AIDS virus (acquired immune deficiency syndrome) are transmitted through the blood and other body fluids.
Preparation of Plasma:
1. Collect blood in a tube with dry anticoagulant. Make sure the tube is not wet. This will cause haemolysis.
2. Mix instantly by gentle inversion. This yield whole blood.
3. Whole blood is now centifuged at 2500 rpm for 10 min. This separates the cellular component of the blood, which goes to the bottom as red-coloured, from liquid component of the blood, which stays at the top.
Preparation of Serum with Centrifugation:
1. Collect blood in a plain tube without any anticoagulation.
2. Allow the blood to clot for 30-60 min at room temperature.
3. Whole blood is now centifuged at 2500 rpm for 10 min. This separtes, the cellular component of the blood, which goes to the bottom as red-coloured, from liquid component of the blood, which stays at the top.
4. Take out the liquid portion (serum) into a separate tube for further use. Serum is commonly used in biochemistry test and serological test.