venipuncture venipuncture in medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous blood sampling (also called phlebotomy) or intravenous therapy. in healthcare, this procedure is performed by medical laboratory scientists, medical practitioners, some emts, paramedics, phlebotomists, dialysis technicians, and other nursing staff. in veterinary medicine, the procedure is performed by veterinarians and veterinary technicians. venipuncture it is essential to follow a standard procedure for the collection of blood specimens to get accurate laboratory results. any error in collecting the blood or filling the test tubes may lead to erroneous laboratory results. venipuncture is one of the most routinely performed invasive procedures and is carried out for any of five reasons: to obtain blood for diagnostic purposes; to monitor levels of blood components; to administer therapeutic treatments including medications, nutrition, or chemotherapy; to remove blood due to excess levels of iron or erythrocytes (red blood cells); or to collect blood for later uses, mainly transfusion either in the donor or in another person. blood analysis is an important diagnostic tool available to clinicians within healthcare. blood is most commonly obtained from the superficial veins of the upper limb. the median cubital vein, which lies within the cubital fossa anterior to the elbow, is close to the surface of the skin without many large nerves positioned nearby. other veins that can be used in the cubital fossa for venipuncture include the cephalic, basilic, and median antebrachial veins. minute quantities of blood may be taken by fingerstick sampling and collected from infants by means of a heelprick or from scalp veins with a winged infusion needle. phlebotomy (incision into a vein) is also the treatment of certain diseases such as hemochromatosis and primary and secondary polycythemia. complications a 1996 study of blood donors (a larger needle is used in blood donation than in routine venipuncture) found that 1 in 6,300 donors sustained a nerve injury. equipment there are many ways in which blood can be drawn from a vein, and the method used depends on the person's age, the equipment available, and the type of tests required. most blood collection in the us, uk, canada and hong kong is done with an evacuated tube system. two common systems are vacutainer (becton, dickinson and company) and vacuette (greiner bio-one). the equipment consists of a plastic adapter, also known as a tube or needle holder/hub, a hypodermic needle and a vacuum tube. under certain circumstances, a syringe may be used, often with a butterfly needle, which is a plastic catheter attached to a short needle. in the developing world, the evacuated tube system is the preferred method of drawing blood. with evacuated or vacuum tubes vacutainer blood bottles greiner bio-one manufactured the first ever plastic evacuated blood collection tube in 1985 under the vacuette brand name. today, many companies sell vacuum tubes as the patent for this device is now in the public domain. these tubes are manufactured with a specific volume of gas removed from the sealed tube. when a needle from a hub or transfer device is inserted into the stopper, the tube's vacuum automatically pulls in the required volume of blood. the basic evacuated tube system (ets) consists of a needle, a tube holder, and the evacuated tubes. the needle is attached to the tube holder by the phlebotomist prior to collection, or may come from the manufacturer as one unit. the needle protrudes through the end of the tube holder, and has a needle on each end. after first cleaning the venipuncture site and applying a tourniquet, the phlebotomist uncaps the needle attached to the tube holder, inserts the needle into the vein, then slides evacuated tubes into the tube holder, where the tube's stopper is pierced by the back end of the needle. the vacuum in the tube then automatically draws the needed blood directly from the vein. multiple vacuum tubes can be attached to and removed in turn from a single needle, allowing multiple samples to be obtained from a single procedure. this is possible due to the multiple sample sleeve, which is a flexible rubber fitting over the posterior end of the needle cannula which seals the needle until it is pushed out of the way. this keeps blood from freely draining out of the back of the needle inserted in the vein, as each test tube is removed and the next impaled. osha safety regulations require that needles or tube holders come equipped with a safety device to cover the needle after the procedure to prevent accidental needle stick injury. fittings and adapters used to fill evacuated tubes from butterfly needle kits and syringes are also available. there are several needle gauges for a phlebotomist to choose from. the most commonly used are as follows: a 21g (green top) needle, a 22g (black top) needle, a 21g (green label) butterfly needle, a 23g (light blue label) butterfly needle, and a 25g (orange or dark blue label) butterfly needle (however this needle is only used in pediatrics or extreme cases as it is so small that it can often result in hemolyzing the blood sample). there are also a variety of tube and bottle sizes and volumes for different test requirements. additives and order of draw the test tubes in which blood is collected may contain one or more of several additives. in general, tests requiring whole blood call for blood samples collected in test tubes containing some form of the anticoagulant edta. edta chelates calcium to prevent clotting. edta is preferred for hematology tests because it does minimum damage to cell morphology. sodium citrate is the anticoagulant used in specimens collected for coagulation tests. the majority of chemistry and immunology tests are performed on serum, which is produced by clotting and then separating the blood specimen via centrifuge. these specimens are collected in either a non-additive tube or one containing a clotting activator. this clotting activator can interfere with some assays, and so a plain tube is recommended in these cases, but will delay testing. tubes containing lithium heparin or sodium heparin are also commonly used for a variety of chemistry tests, as they do not require clotting and can be centrifuged immediately after collection. a combination of sodium fluoride and potassium oxalate is used for glucose tests, as these additives both prevent clotting and stop glycolosis, so that blood glucose levels are preserved after collection. another specialty tube is an opaque amber colored tube used to collect blood for light sensitive analytes, such as bilirubin. test tubes are labeled with the additive they contain, but the stopper on each tube is color coded according to additive as well. while colors vary between manufacturers, stopper colors generally are associated with each additive as listed below. because the additives from each tube can be left on the needle used to fill the tubes, they must be drawn in a specific order to ensure that cross contamination will not negatively affect testing of the samples if multiple tubes are to be drawn at once. the "order of draw" varies by collection method. below in the order of draw generally required for the evacuated tube system (ets) collection method are the most common tubes, listing additive and color: vacutainer/sample tube types for venipuncture/phlebotomy tube cap color or type in order of drawadditiveusage and comments blood culture bottlesodium polyanethol sulfonate (anticoagulant) and growth media for microorganismsusually drawn first for minimal risk of contamination. two bottles are typically collected in one blood draw; one for aerobic organisms and one for anaerobic organisms. light blue sodium citrate (weak calcium chelator/anticoagulant)coagulation tests such as prothrombin time (pt) and partial thromboplastin time (ptt) and thrombin time (tt). tube must be filled 100%. plain red no additiveserum: total complement activity, cryoglobulins gold (sometimes red and grey "tiger top") clot activator and serum separating gelserum-separating tube: tube inversions promote clotting. most chemistry, endocrine and serology tests, including hepatitis and hiv. dark green sodium heparin (anticoagulant)chromosome testing, hla typing, ammonia, lactate light green lithium heparin (anticoagulant)plasma. tube inversions prevent clotting lavender ("purple") edta (chelator / anticoagulant)whole blood: cbc, esr, coombs test, platelet antibodies, flow cytometry, blood levels of tacrolimus and cyclosporin pink edta (chelator / anticoagulant)blood typing and cross-matching, direct coombs test, hiv viral load royal blue edta (chelator / anticoagulant)trace elements, heavy metals, most drug levels, toxicology tan edta (chelator / anticoagulant)lead gray sodium fluoride (glycolysis inhibitor) potassium oxalate (anticoagulant) glucose, lactate yellow acid-citrate-dextrose a (anticoagulant)tissue typing, dna studies, hiv cultures pearl ("white") separating gel and (k2)edtapcr for adenovirus, toxoplasma and hhv-6 in children further information: pain management in children use of lidocaine iontophoresis is effective for reducing pain and alleviating distress during venipuncture in children. a needle-free powder lignocaine delivery system has been shown to decrease the pain of venipuncture in children. rapid dermal anesthesia can be achieved by local anesthetic infiltration, but it may evoke anxiety in children frightened by needles or distort the skin, making vascular access more difficult and increasing the risk of needle exposure to health care workers. dermal anesthesia can also be achieved without needles by the topical application of local anesthetics or by lidocaine iontophoresis. by contrast, noninvasive dermal anesthesia can be established in 5–15 min without distorting underlying tissues by lidocaine iontophoresis, where a direct electric current facilitates dermal penetration of positively charged lidocaine molecules when placed under the positive electrode. one study concluded that the iontophoretic administration of lidocaine was safe and effective in providing dermal anesthesia for venipuncture in children 6–17 years old. this technique may not be applicable to all children. future studies may provide information on the minimum effective iontophoretic dose for dermal anesthesia in children and the comparison of the anesthetic efficacy and satisfaction of lidocaine iontophoresis with topical anesthetic creams and subcutaneous infiltration. non-pharmacological treatments for pain associated with venipuncture in children includes hypnosis and distraction. these treatments reduced self reported pain and when combined with cognitive-behavioural therapy (cbt) the reduction of pain was even greater. other interventions have not been found to be effective and these are suggestion, blowing out air, and distraction with parent coaching did not differ from control for pain and distress. with needle and syringe some health care workers prefer to use a syringe-needle technique for venipuncture. sarstedt manufactures a blood-drawing system (s-monovette) that uses this principle. this method can be preferred on the elderly, those with cancer, severe burns, obesity, or where the veins are unreliable or fragile. because syringes are manually operated, the amount of suction applied may be easily controlled. this is particularly helpful when veins are small which may collapse under the suction of an evacuated tube. in children or other circumstances where the quantity of blood gained may be limited it can be helpful to know how much blood can be obtained before distributing it amongst the various additives that the laboratory will require. another alternative is drawing blood from indwelling cannulae. blood cultures there are times when a blood culture collection is required. the culture will determine if there are pathogens in the blood. normally blood is sterile. when drawing blood from cultures use a sterile solution such as betadine rather than alcohol. this is done using sterile gloves, while not wiping away the surgical solution, touching the puncture site, or in any way compromising the sterile process. it is vital that the procedure is performed in as sterile a manner as possible as the persistent presence of skin commensals in blood cultures could indicate endocarditis but they are most often found as contaminants. it is encouraged to use an abrasive method of skin preparation. this removes the upper layers of dead skin cells along with their contaminating bacteria. povidone-iodine has traditionally been used but in the uk a 2% chlorhexidine in 70% ethanol or isopropyl alcohol solution is preferred and time must be allowed for it to dry. the tops of any containers used when drawing a blood culture should also be disinfected using a similar solution. some labs will actively discourage iodine use where iodine is thought to degrade the rubber stopper through which blood enters the bottle, thus allowing contaminates to enter the container. the blood is collected into special transport bottles, which are like vacuum tubes but shaped differently. the blood culture bottle contains transport media to preserve any