The Theory of Bloodtaking [Student BMJ]

A theoretical framework for the safe practice of venepuncture
Robert Lord explains step by step how to take blood from adults safely and without too much bloodshed

Venepuncture ("taking blood") is one of the basic practical skills that needs to be acquired by medical students.1 Although in hospitals routine samples are increasingly being obtained by phlebotomists employed on the wards and in outpatient departments, it is the doctor who will be called on for the "difficult patient." It is therefore worth while obtaining plenty of experience as a medical student. This article aims to give a theoretical background to venepuncture and to offer a few tips arising out of my own experience as a venepuncture training coordinator. I have restricted the discussion to adults, as paediatric patients often require a different approach.

The aim of venepuncture
The aim of venepuncture is to obtain a blood sample of adequate volume for the tests requested, with due attention paid to avoid preanalytical interference, into the correct tubes for analysis, safely, and with the minimum of discomfort for the patient.

Preanalytical factors
The results of many analyses will be influenced by preanalytical factors.2 Some tests require the patient to fast, some require taking at a specified time of day or are related to the time of ingestion of a drug (for example, therapeutic drug monitoring). Many samples need to be separated in a centrifuge within a short time of venepuncture (some immediately) to avoid erroneous results. Haemolysis of the sample needs to be avoided. If you are in any doubt about special requirements for a test, contact the laboratory first and ask, otherwise the blood sample may not be suitable for analysis.

Basic anatomy
Blood for most tests is obtained from a vein. The most common area in which a vein is located for venepuncture is the antecubital fossa, the area in front of the elbow. Veins are quite variable in their position. They are also quite "wobbly," so the arm should be extended to provide longitudinal tension to hold the vein in place.
"Mobile" veins can be anchored with a thumb at about an inch below the venepuncture site.
It is important to note the structures sited medially in the antecubital fossa - the brachial artery and the median nerve. A needle should not be inserted deeply in this area.
If there is no obvious vein in the antecubital fossa, the lateral area of the forearm and the back of the hand should be examined. Very rarely venepuncture may need to be carried out in the foot or the femoral vein in the groin region.
It is worth while asking patients if they have a vein that is usually "successful."

Finding a vein
A tourniquet is a device used to help "bring up" veins by restricting the flow of blood up the arm through superficial veins. Many different types are available. Try to use a type that is the most comfortable when applied to the arm. Tourniquets need to be replaced at regular intervals (and always if they are splashed with blood) as they can become sources of infection.3 4
Do not put the tourniquet too near the venepuncture site, it should be at least two inches away. When using the tourniquet it is important not to pinch the skin, which is easily done in elderly people. Adequate restriction of blood flow needs to be achieved without the tourniquet being too tight, as this will cause discomfort for the patient, and the higher pressure in the vein may cause leakage of blood around the needle or even spurting of blood. Don't keep the tourniquet on for too long - it starts to become uncomfortable for the patient.
The sign of a "good" vein is that it stands out when the tourniquet is tightened and goes down when the tourniquet is released. The vein should feel springy, and in this respect touch is often more important than sight in finding a suitable vein. A vein may stand out very well but be totally thrombosed - often seen after repeated venous cannulation for chemotherapy or in drug addicts.
Various manoeuvres may help to make a vein more prominent.5-7 Gentle tapping over the vein and the application of warmth, using warm water, air, or a covering, can sometimes be useful.

Paediatric blood taking
Pain relief and sedation
EMLA cream should be applied to venepuncture site 45 minutes before procedure whenever possible. Paracetamol/Chloral is essential against pain and fever.
An assistant should always be on hand to help restrain the child. It is best to perform the procedure inside a treatment room, while the parents wait by the bedside or go out of the ward.

Blood collection
Antecubital veins can be used in older children (usually over 2 years). Below that age use veins on the dorsum of the hands or feet; use either a butterfly or, in more difficult cases, the hub of a 20g needle may be broken off and the needle passed through the skin along the line of a vein - once punctured, the blood will drip back through the end of the needle.
In neonates/babies a heel prick sample will often yield enough blood. This is especially useful for FBC, serum bilirubin and drug levels. Holding the foot in one hand with the heel facing down, prick the heel just lateral to the midline (avoid the midline as you can cause osteomyelitis of the calcaneum) and squeeze. Allow a generous drop of blood to accumulate before drawing it into a capillary tube or scooping it up with the mini-tube. If the blood starts to spread all over the skin, wipe it away with a dry gauze, and hold the heel such that the puncture site points vertically down. After squeezing, release your grip until the skin turns pink again before squeezing out another drop. In larger children, you may use a similar method on the fingers, much like doing a hypocount.
If procedures fail blood can be obtained from the brachial artery.

Usually relatively easy in neonates (24G or 26G) or older children (over 2 - 3 years 22G or bigger). The same sites as indicated for blood collection can be used, as can scalp veins in infants. But do not waste time! Consider alternatives (intraosseus route, IM medication).

Investigations in Paeds A&E
1. In the ED, investigations are needed only A) to help make diagnosis (see note below) and B) samples needed for culture prior to antibiotics
2. However, if taking blood is required take enough and some spare! Consider the investigations which may be needed and/or store the blood (clotted tube). Venesection is traumatic for the children and to go back for more blood is cruel! (e.g.. when taking blood for FBC, always take blood for blood culture in case it is required).
3. Do not be afraid to investigate in the ED where appropriate - time obtaining samples and waiting for results can be invaluable for observing children in the department and waiting for Chloral to work!

Needle systems & Equipment
Once a suitable vein has been located a needle needs to be inserted into it to withdraw blood. There are basically three types of system. The details of each will vary between hospitals depending on the company used for equipment supply.

Combined needle and valve
This is the system most commonly in use now. It was developed with the concept of safety being of prime importance. The Vacutainer(TM) system will be described as an example.
The needle is a combined needle and valve. This is screwed into an open-ended plastic cylinder. The needle should be angled at about 20-40 degrees, bevel upwards, to enter the vein. Inserting at too shallow an angle may cause unnecessary pain and allow the vein to roll out of the way. Inserting at too steep an angle may cause the vein to be transfixed. The needle should never be bent before undertaking venepuncture. A tube is inserted into the plastic cylinder. Blood is drawn automatically into the tube by the presence of a vacuum in the tube. When the tube is removed the valve seals the needle until another tube is placed in the cylinder. Once all the specimens are collected the needle is withdrawn. This system has a great advantage in that the blood flows from the patient's vein directly into the tube for analysis, making it a safer and more rapid process. There is, however, no control over the speed at which blood is removed from the vein, and skill is required to ensure that the needle is not dislodged from its position in the vein on changing tubes; counterpressure exerted on the flanges of the plastic cylinder is required as the tubes are inserted and removed.

Needle and syringe
Although used less, this remains a useful method, especially in the more difficult venepuncture. A green (21 gauge) needle is usually selected and attached to a syringe, commonly 5 ml, 10 ml, or 20 ml. The vein is entered, and the plunger is gently pulled to draw up blood into the syringe; too rapid aspiration can result in haemolysis. The needle is then withdrawn from the vein once the required amount of blood has been taken. The blood then needs to be put into the appropriate tubes for analysis. This can be done either by placing the tubes in a rack (NEVER held in the hand) and then piercing the top with the needle - with a vacuum tube the blood is drawn into the tube without the need to push on the plunger of the syringe - or by removing the needle using the grip on a "sharps box," removing the top from the tube and pushing on the plunger of the syringe to dispense the blood into the tube. This system has the advantage of seeing a small "flashback" of blood into the syringe on entering the vein and greater control over the withdrawal of blood. However, there is more opportunity for a needlestick injury.

This system is useful for obtaining blood from the back of the hand, in children, in elderly confused patients, and whenever difficult venepuncture is encountered. The length of tubing attached to the needle allows for a degree of movement of the patient's arm during phlebotomy. Both syringes and a VacutainerTM attachment can be used (although the former provide better control). If possible, it is recommended that two people be present, one to hold the needle in place once the vein has been entered, and another to operate the syringe to collect the blood. Don't forget that the tubing itself contains a useful volume of blood for analysis.

The following should be noted for whatever needle system is used.
Before piercing the skin with the needle the skin should be wiped with an isopropyl alcohol swab. Although bacteria will not be totally eradicated by this, dirt and grease are removed from the skin. In addition it can make the skin easier to pierce in elderly people. It looks professional, and patients expect it. Don't pierce the skin immediately after swabbing since this can result in an unpleasant stinging sensation for the patient.8 Dry the skin with cotton wool. The only exception to this rule is when taking blood for alcohol analysis.
Cotton wool ball
It is vitally important that haemostasis is achieved before the doctor and patient part company, especially if the patient is taking warfarin. Once the needle has been withdrawn from the vein a piece of cotton wool should be pressed firmly over the puncture site. Depending on the patient this can be done either by the doctor or the patient. It should be noted, however, that patients tend not to press for long enough and minor bruising at the puncture site can be common.9 Major bruising should not occur if adequate time and pressure are achieved for haemostasis. Failure to do this can result in a large painful haematoma that may affect nearby structures. It is not recommended to use the tourniquet to apply pressure over the cotton wool. The tourniquet may slip or become contaminated with blood seeping through the cotton wool.
Adhesive bandage
Remember that some people are allergic to plasters, so ask the patient before putting a plaster over the puncture site. Allergic reactions can give rise to considerable skin discomfort and an unhappy patient.
Sharps bin
The needle MUST be disposed of carefully as soon as it has been used. A needle should NEVER be resheathed. It is therefore important that a sharps bin is at hand when undertaking venepuncture. The sharps bin should always be carried using the handle. The bin has specially designed indents at the top to enable the safe removal of a needle into the bin. Do not attempt to retrieve any item from a sharps bin. Do not overfill. When "full," close the bin and use the locking mechanism so that the bin is ready for disposal.
Many different tubes are available for different analyses. If in doubt about the type of tube required for the test, do contact your pathology department first as the staff should be able to help. The different tubes often contain different additives so that blood should NEVER be decanted from one bottle to another since this may markedly affect some of the tests that are performed on the sample.10
Tubes should be labelled with the patient's details once the blood has been taken. GXM tubes must be signed on the tube and forms.
Most tests require only a small volume of blood, so that often a full tube is not needed. It should be borne in mind, however, that in a very small blood sample the anticoagulant may dilute the blood sufficiently to affect the results. "Paediatric" tubes are available, which can be useful in difficult adult patients.
Amount of blood needed
The safest way is to allow the vacuum tube to suck up as much blood as it wants. Having said that, the only tubes which must be filled strictly to the mark are PT/PTT(Sodium Citrate)(Blue)tubes [4mls in SGH]. FBC(CBC/Heparinized)(Purple) tubes should NOT be filled to the brim lest they clot, but rather to the limit of suction [2mls in SGH, about half the tube]. Although plain tube(Yellow) will suck up 4mls of blood, half the tube is sufficient for a large battery of tests. Similarly for a group and cross match tube [4mls], where 1ml is often more than enough. The microbiologists recommend you put at least 5mls in each culture bottle, which most of us treat as theory rather than practice. Always gently shake/invert your tubes, especially the FBC and PT/PTT ones, to mix the additives and prevent clotting.
Paediatric blood tubes
These are similar to adult ones, except the are smaller. The FBC tube requires only 0.5mls (1st mark in KK), and it comes with a scoop edge for use in finger/heel pricks. The general rule I use for Paeds plain tubes(2mls) is, "1 mark for 1 test", ie. 0.5mls per test. Therefore 1ml is usually enough for a U/E and LFT. Nonetheless, if the blood supply is good, fill as much as you can.

Illegal tips and tricks

Pouring out blood
Never, never, ever pour out blood if you're not sure what you're doing. You may go from having 1 test to none, instead of 1 test to 2. In general, pour out only from plain tubes. The exception to this rule is from a PT/PTT tube into an FBC tube, although this should be reserved for really desperate situations as it can affect your PT/PTT result. Always pour out as soon as you can, and shake the tube before pouring. If the sample is partially clotted, you must pour the entire tube out (not just the serum bit), and then shake well and hope the heparin dissolves some of the clots. If you still see lumps, don't despatch the tube - a misleading result causes more trouble than no result.
Storing blood
This is sometimes a necessity for many reasons: "Office-hour only" tests, Needing to send paired samples (eg peak/trough levels, or blood-urine pairs). Always label your tubes with the name and date/time taken, and put them in the fridge.
Know which samples can and which can't be stored. From shortest to longest: ABG(never store), PT/PTT (few hours), FBC/ESR(overnight), most plain tube tests (1 day), serology (few days). Cultures(esp urine and stool) should also never be stored, lest they grow some weird bugs. Do note that K+ and glucose start rising the moment the blood is taken, and are inaccurate beyond 6-8 hours.
Common tests in SGH that are "office hour only" include: CRP, ESR, timed-drug levels. (If you are doing U/E and CRP at 9pm but don't feel comfortable keeping blood, send 2 plain tubes with 2.5ml each, instead of 1 with 5 mls: the lab will keep one for you and run the CRP the next day.)
Don't forget there are alternative tests you can do: Urine dipstick instead of Feme. Urine dipslide instead of Urine culture, when you plan on starting antibiotics in the middle of the night.

General aspects
It is important to wear a white coat or equivalent when performing venepuncture.
Handwashing is the single most important method available to reduce cross-infection.
Wash your hands before leaving the work area. Never eat or drink when carrying out your work.
Category 3 samples
Organisms are categorised according to the danger they pose to people. "High risk" or "category 3" patients (most commonly those with HIV or AIDS, hepatitis B or C, and some forms of tuberculosis) need to have this status written on the request form to inform the laboratory handling the samples. Having said this, there will be many patients who, unbeknown to the doctor, are "high risk." For this reason one should treat every blood sample as potentially infectious and work carefully.11
Needlestick injuries
Gloves will protect only from splashes, and a needle will pierce the material, although the inoculated dose of any organism may be reduced with some types of gloves.12-15 Some people find that gloves reduce the tactile sensation necessary to find a vein. Different glove materials - for example, nitrile - are available if allergy to latex develops.16 In the event of a needlestick injury the affected part should be placed under running water and encouraged to bleed if the skin has been broken. If a needlestick injury does occur, however trivial, you MUST report it to the occupational health department so that any treatment (for example, prophylaxis against HIV) can be instituted.17 18
The risk of developing HIV after needlestick injury while treating an HIV positive patient is estimated at about 0.3-0.4% whereas for hepatitis it may be as high as 30-40%, which means that the risk of developing hepatitis is over 100 times greater than that of becoming infected with HIV.19 It is thus vitally important that you have had a course of hepatitis B vaccination and that your antibody concentrations have been checked.20

Arterial puncture
If an artery is punctured the blood is red and easily aspirated. It is unlikely that any damage is caused.21 22 It is important, however, to apply firm pressure over the puncture site for at least five minutes.
Nerve injury
Rarely, a nerve may be irritated or injured during venepuncture.23 The patient may complain of a tingling sensation and pain in their arm. It is important to take note of this since some patients may go on to develop persistent pain, which can be successfully treated if treatment is instituted early.24 This type of injury is obviously best avoided by superficial placement of the needle, avoiding the medial aspect of the antecubital fossa if possible, and not using a jabbing motion with the needle on insertion.25
Patient faints (syncope)
Syncope or near syncope can be quite common and is best avoided. Patients may say that they do not like needles or that they have fainted in the past. If this is the case, then it is best that they lie on a bed to have their blood taken rather than in a chair.
If patients do voice concern that they are feeling faint while sitting in a chair then try and get their head as low as possible. Call for help. If a patient faints, try to get him or her into a horizontal position, with the legs elevated. If patients have what seems to be a fit, then protect them from injuring themselves and place them in the recovery position. An electrocardiogram and further treatment may be required.26
Failure of venepuncture
We will all fail to get blood out of someone at some time in our work. Do not turn your patient into a pin cushion. Ask someone else more experienced to take over as they will be less frustrated than you, and the patient will also appreciate this.
Remember, venepuncture is a procedure that requires informed consent, and patients may refuse to have blood taken. They may also refuse additional attempts if previous attempts have failed.27

Venepuncture is an art, and good technique comes with practice. Each patient is different, and a good doctor is one who treats each patient with respect and courtesy so that the patient's experience of having blood taken is not unduly unpleasant.


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4 Berman DS, Schaefler S, Simberkoff MS, Rahal MS. Tourniquets and nosocomial methicillin-resistant staphylococcus aureus infections. New Eng J Med 1986;315:514-5.

5 McLaren P. Dilating peripheral veins. Anaes Int Care 1994;22:318.

6 Robbins PM. Dilating peripheral veins. Anaes Int Care 1995;23:654-5.

7 Wishaw J. Dilating veins, a simple approach. Anaes Int Care 1995;23:123.

8 Horanitz PJ, Cembrowski GS, Bachner P. Laboratory phlebotomy; College of American Pathologists Q-probe study of patient satisfaction and complications in 23 783 patients. Arch Pathol Lab Med 1991;115:867-72.

9 Galena HJ. Complications occurring from diagnostic venipuncture. J Family Prac 1992;34:582-4.

10 Walmsley RN, White GH. A guide to diagnostic clinical chemistry. 2nd ed. London: Blackwell Scientific Publications, 1988.

11 Gordin FM, Gibert C, Hawley HP, Willoughby A. Prevalence of human immunodeficiency virus and hepatitis virus in unselected hospital admissions; implications for mandatory testing and universal precautions. J Infect Dis 1990;161:14-7.

12 DeGroot-Kosolcharoen J. Pandemonium over gloves: use and abuse. Am J Infect Control 1991;19:225-7.

13 Kaczmarek RG, Moore RM, McCrohan J, Arrowsmith-Lowe TJ, Caquelin C, Reynolds C, et al. Glove use by health care workers: results of a tristate investigation. Am J Infect Control 1991;19:228-32.

14 Stringer B, Smith JA, Scharf S, Valentine A, Walker MM. A study of the use of gloves in a large teaching hospital. Am J Infect Control 1991;19:233-6.

15 Mast ST, Woolwine JD, Gerberding JL. Efficacy of gloves in reducing blood volumes transferred during simulated needlestick injury. J Infect Dis 1993;168:1589-92.

16 Dillard SF, MacCollum MA. Reports to the FDA: Allergic reactions to latex containing medical devices. International latex conference. Sensitivity to latex in medical devices. 1992;23. (Abstract.)

17 Easterbrook P, Ippolito G. Prophylaxis after occupational exposure to HIV. BMJ 1997;315:557-8.

18 Guidelines on post-expose prophylaxis for health care workers occupationally exposed to HIV. UK Department of Health, June 1997.

19 Horanitz PJ, Schifman RB. Phlebotomists' safety practices: a College of American Pathologists Q-probes study of 683 institutions. Arch Pathol Lab Med 1994;118:957-62.

20 Choudhury RP, Cleator SJ. An examination of needlestick injury rates, hepatitis B vaccination uptake and instruction on "sharps" techniques among medical students. J Hosp Inf 1992;22:143-8.

21 Tekinalp H, Alpagut U. Pseudoaneurysm formation is a known complication of both arterial manipulations and arterial injuries. J Pediat Surg 1996;31:1197.

22 Demircin M, Peker O, Tok M, Ozen H. False aneurysm of the brachial artery in an infant following attempted venepuncture. Turk J Pediat 1996; 38:389-91.

23 Newman BH, Waxman DA. Blood donation-related neurologic needle injury: evaluation of 2 years' worth of data from a large blood centre. Transfusion 1996;36:213-5.

24 Berry PR, Wallis WE. Venepuncture nerve injuries. Lancet 1977;ii:1236-7.

25 Horowitz SH. Peripheral nerve injury and causalgia secondary to routine venipuncture. Neurology 1994;44:962-4.

26 Lipton JD, Forstater AT. Recurrent asystole associated with vasovagal reaction during venipuncture. J Emerg Med 1993;11:723-7.

27 McConnell AA, Mackay GM. Venepuncture: the medicolegal hazards. Postgrad Med J 1996; 72:23-4.

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