Collection of blood in the laboratory

Introduction

Blood collection is a process of withdrawing blood from a patient; phlebotomist is a person that withdraws blood from patient, for medical testing, transfusion, donation or research. Blood can be collected from various areas in the body which are the femoral vein, arterial vein, anticubital fossa vein. Blood collection is done in various ways such as vein-puncture, capillary puncture, heel-stick for infants; femoral vein blood collection in the laboratory is normally collected from patients by a trained phlebotomist (Jeon, 2011).

Types of blood collection

There are various sites in the body where blood can be collected for laboratory investigation these include;

Venous blood collection.
Capillary blood collection.
Heel-stick for infants.
Femoral vein.

Venous blood collection

Venous blood is deoxygenated blood that flows from tiny capillary blood vessels within the tissues unto progressive larger veins to the right side of the heart; venous sample of blood is obtained from the anticubital vein when a larger volume is needed, if serum is required the needle is detached and the blood is carefully delivered unto a clean dry sterile and labelled container in haematological examination, requiring the use of clotted specimen, the blood is collected into an anticoagulant container, the blood is mixed promptly and thoroughly but gently to prevent frothing and damage to cells (Abayomi, 2007).

Capillary blood collection

Capillary blood is obtained from the capillary beds that consist of the smallest veins and arteries of the circulatory system capillary blood is obtained from skin puncture; with a lancet it is satisfactory in adults with difficult veins and mostly in infants and children for full blood count, sickling and other test that do not require large quantity of blood.

Heel stick blood collection

Heel stick blood collection is a simple procedure in which a new born baby heel is pricked and then a small amount of the blood is collected usually with a narrow gauge (capillary) glass tube or filter paper. Heel sticks are the most common performed invasive procedure in neonatal intensive care units (Baker, 2005).

Femoral vein

Femoral pulse is located just below the inguinal ligament at the junction of the middle thirds of the ligament; femoral tap generally for infants less than six months required amount of blood is collected from femoral tap and it is preferably performed by a physician when there is difficultly in collecting of blood from other vein, the patient legs are slightly abducted, the body and arms are immobilized by an assistant.

Procedure for blood collection

The first step in acquire a quality laboratory test result for any patient is the specimen collection procedure. The venipuncture procedure is complex, required both knowledge and skill to perform several essential steps are required for every successful collection procedure.

Venipuncture procedure

If large volumes of blood are required, a venous sample of blood must be obtained from the patient.

Materials needed

70% alcohol swab

Syringe and needles

Tourniquet

Container

Hand gloves and lab coat

Select a sterile dry preferably plastic syringe of the capacity required, e.g. 2 ml, 5 ml, or 10 ml attach to it a 19 or 20 SWG needle if the patient is a child or adult with small vein, use a 23 SWG needle.
Apply tourniquet to the upper arm of the patient, do not apply the tourniquet too tightly.
Ask the patients to make a tight fist which will make the veins more prominent.
Using the index finger, feel for a suitable vein, select a sufficiently large straight vein that does not roll.
Cleanse the puncture site with 70% alcohol and allow to dry do not re-touch the cleansed area.
Remove needles cap and insert into the vein, once blood begin to flow ask the patient to open his/her hand, release tourniquet and remove needle, immediately press on the puncture site with a piece of dry cotton wool.
Remove the tourniquet completely
Remove needle from syringe and carefully fill the container with the required volume of blood. Discard needle safely into the hazard bag.
Mix immediately the blood into the appropriate containers.

Precaution for vein puncture

Avoid prolong venous collection of blood.
Avoid touching the swab areas with hands after swabbing the sites.
Tourniquet should not be too tight.
The alcohol used to clean the skin must be allowed to dry before collecting blood to avoid haemolysis.

Capillary blood collection

Capillary blood is mainly used when the patient is an infant or young child and the volume of blood required is small.

Materials needed

Capillary tube

Cotton wool

Lancet

Alcohol Swab

Procedure for capillary puncture

Cleanse the puncture area with 70% alcohol, allow the area to dry.
Using a sterile lancet, make a rapid puncture, sufficiently deep to allow the free flow of blood at the ring finger.
Wipe away the first drop of blood with a dry piece of cotton wool and fill the capillary tube with the next few drops of blood.
When sufficient blood has been collected, press a piece of dry cotton wool over the puncture area until bleeding stops.

Precautions for capillary puncture

Avoid squeezing site of collection too hard.
Avoid the use of broken capillaries for collecting blood.
Allow blood to flow free into the container and not scraping off the skin surface.
Clean up the first drop of blood before allowing the second flow into the capillary tube.

Heel sticks for infants

Materials needed

Cotton wool

Lancet

Capillary tube

Filter paper card

Procedure for heel sticks for infants

Pre warm the infant’s heel i.e. to increase the flow of blood for collection.
Massage the heel of infant.
Cleanse the site with alcohol swab and allow it to dry.
Hold the baby’s foot firmly to avoid sudden movement.
Use the lancet puncture the heel and wipe away the first drop of blood.
Fill the capillary tubes or filter paper card as necessary.
Apply dry cotton wool to the puncture site to stop bleeding. (Monica 2006).

Precaution for heel-stick

Avoid squeezing site too hard.
Avoid puncturing the infant heel too deep.
Do not puncture the area between the imaginary boundaries.
Do not puncture areas of the foot other than the heel.
Do not puncture the baby’s heel twice.
Do not puncture site if there is bruises.

Femoral vein

Materials needed

Cotton wool
Syringes and needle
Containers
Hand gloves

Procedure

Put on gloves and instruct the patient to lie down on the examination table and set up you collection materials.
The patient should spread his/her leg as wide as comfortable and search for the femoral vein.
Clean site thoroughly with an alcohol swab, while the site is drying up, open a new needle and syringe.
Insert the needle into the femoral vein and begin to withdraw blood, instruct the patients to breathe normally.
When the syringe is filled remove and place a dry swab at the collection site, add pressure for some minutes.
Check for bleeding before applying a bandage or cotton wool with surgical tape; instruct the patient to avoid lifting or vigorous activities for about 24 hours.
Dispose of the needle in sharp container label blood collection tube and take to the laboratory for processing.

Precautions

Avoid prolong stay of needle in the collection site.
Avoid touching the swab area with hands.
Allow alcohol used to clean the site to dry before proceeding for the draw.
Avoid puncturing the site more than twice.

Anticoagulants

An anticoagulant is a chemical substance which when added to blood, prevent it from clotting. It removes or inactivates one or more blood coagulation factors.

Types of anticoagulant for laboratory use

EDTA (Ethylene Diamine Tetra Acetic Acid)
Lithium Heparin
Fluoride Oxalates
Plain Containers

Mode of action of each anti-coagulant

EDTA (Ethylene Diamine Tetra-Acetic Acid):

EDTA, commonly called sequestrene, is a powerful and excellent anticoagulant of choice for routine laboratory work.

Principle

EDTA, acts by chelating calcium ion and preserves cellular element better than oxalates. The dipotassium or disodium salt of EDTA is used, but the former is preferred to the later because it is more soluble. It is prepared as a 10% solution and used at a concentration of 2mg/ml of blood. It is either used in liquid form or in the crystal form. An excess of EDTA, causes shrinkages and degenerative changes in red cells.

Preparation

Dipotassium salt of EDTA—10g

Distilled water —– 100ml

Dissolve the salt in distilled water, deliver the solution into 5ml bottles, allow the water content of the solution to evaporate at room temperature, fix caps to tube and label appropriately.

Uses

EDTA is the Anticoagulants of choice for haematological tests.
It preserves blood better than the double oxalates.
Blood can be used for total white cell count, pcv, platelet count, differential white cell count.

Sodium Fluoride and Potassium Oxalate:

The combination of oxalate of potassium and sodium fluoride is specially designed for blood glucose and alcohol estimation.

Principle

The oxalate acts as the anticoagulants by combing with calcium to form insoluble calcium oxalate, thereby preventing the calcium from being used in the clotting process. While the fluoride acts as an enzyme inhibitor by preventing glycolysis.

Uses

It is used to preserve glucose in whole blood

Lithium Heparin:

This is a physiological anticoagulant present in the blood. The commercial types come as lithium heparin.

Principle

It acts by inactivating prothrombin, thereby preventing it’s conversion to thrombin and thus preventing the conversion of fibrinogen to fibrin. It is the most expensive anticoagulant.

Uses

It is mostly used for collecting samples meant for electrolyte estimation such as Na+, K+, Cl, HC^–
For bilirubin estimation
For ph enzymes Assay.
For liver and kidney function test

Plain container:

These are container with no anticoagulant. They are mostly used in chemistry laboratory, is a 5ml-10ml glass tube with red top for the purpose of producing serum for most laboratory procedure.

Uses

It is used for most clinical chemistry test and immunological test, hormonal assay test, Amlayse test, Alanine Aminotransferase ALT, SGPT. [Abayomi 2007].

Raising request form

Laboratory request forms provide information about the laboratory test being requested for. They carry demographic data and other information about the patient. In raising request form, what should be put in place are;

The name of the patient i.e. the first and last name of the patient, one name should not be accepted in the case of two person’s bearing of the same names to avoid missed up of results and sample.
The age of the patient: the patient should be able to give the exact number of his/her age.
The sex of the patient must be added in the request form to be able to differentiate if it is a male or a female.
The kind of test to be carried out must be written down on the request form e.g. pcv, full blood count, urinalysis, fasting blood sugar.
The date and time of the test request must be written on the request form.
Laboratory number
Date of request
Requesting officer
Clinical details

Labelling of sample

A properly labelled sample is essential so that the result of the test match the patients request form. The key elements in labelling of sample are;

Patient name
Patient identity number
Date and time of sample collection must be labelled on each tube.
The kind of test to be carried out must be labelled on the appropriate container.

Transportation of specimen

It is always the best rule to dispatch the specimen to the laboratory after collection as soon as possible, as further safety measure to prevent transmission of deterioration chemical change in some clinical data takes place very quickly at room temperature. These changes can be minimised by keeping the specimen at 4^oC for up to 2 hours. The regulation for transporting specimen include:

All blood samples must be placed on a transport bag after collection and dispatched safety to each unit.
All blood container must be completely closed to avoid spillage of samples
Sample must be placed in leak proof containers. (Ochei 2007).

Techniques to avoid haemolysis

Mix all tubes with anticoagulant additives gently, avoid shaking vigorously
Avoid drawing blood from a haematoma: select another collection site.
When using needle and syringe, avoid drawing plunger back to forcefully
Make sure the site for collection is dried before proceeding withdraw
Avoid prolonged tourniquet application
Avoid massaging, squeezing or probing a capillary site
Avoid excessive fist clenching

Safety precaution in blood collection

Always put on laboratory coats and hand gloves when collecting blood samples
Always use one glove for per-patients to avoid transfer of blood pathogen to another patient

Always keep your working benches and table clean

Always label container before proceeding for blood drawn
Do not recap used needles, used needles and syringe and other sharp objects should be put in a bio-hazard bag
Avoid chewing gums when collecting blood samples

Hands must be washed after blood collection

Conclusion

Blood collection is a vital process in the laboratory for investigation of diseases in normal and abnormal condition, as such it is important for blood collection to be performed in an aseptical manner using the appropriate containers and equipment to be able to achieve better results. It is recommended that those involved in blood collection must be skilled and knowledgeable.

References

Abayomi A (2007): A Test book for Medical Laboratory Practice, 1^st Edition pp.185-187

Kochatkar, J. O. (ed) (2007): medical laboratory science theory and practice, Tata McGraw-Hill Publishing Company Limited 6^th Edition pp.91-93.

Barker, D. B. (Ed) (2005):, Blood collection for neonatal screening programme, Clinical Laboratory Standard 74:139-140.

Jeon, B. R. (2011): Improving blood collection process using the active phelebotomist phelebotomy system “Clinical Laboratory” 57 (1-2) : 21-27

Monica. C. (ed) (2006): district laboratory practice in tropical countries (part 2) Cambridge University 2^nd Edition pp.296-298.