Blood How Coll

8/12/2019 Blood How Coll

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So Youre Going to Collect a Blood Specimen: An Introduction to Phlebotomy 7

How Is Blood Collected?Blood is usually collected into plastic tubes (rarely glass tubes) called evacuated tubes. The tubescontain a vacuum, which assists in the filling of the tube. The evacuated tubes have a stopper witha septum that is punctured by a needle assembly during the blood draw. Usually a plastic safetyclosure surrounds the stopper. Blood also may be collected by syringe for transfer into other typesof containers, such as blood culture bottles (see page 46). It is important to allow the tube to fillby vacuum instead of removing the stopper. This is most critical for laboratory tests, such asprothrombin time (PT) and activated partial thromboplastin time (APTT), where fill volume isimportant to ensure the proper anticoagulant-to-blood ratio. In general, the stopper should neverbe removed from the blood tube.

Venipuncture, using a needle and tube, is the most commonmethod for the collection of blood. On some occasions, blood maybe collected by puncturing the skin with a retractable lancet

device. Specially trained health care professionals may obtainblood from intravascular access devices (see Appendix 1) or thebone marrow cavity (see Appendix 2) using a syringe.

Blood may be collected into a tube without any anticoagulant andthen allowed to clot. When a clot forms, a liquid called serum isproduced. To promote clotting, blood may be collected in a serumseparator tube or a plain serum tube. Serum separator tubescontain a clot activator as well as a gel, the latter forming a barrierto separate the serum from the cells during and aftercentrifugation. Serum is used for many tests.

Blood also may be collected into a tube containing ananticoagulant, which prevents clotting. The blood then may beused in whole form, the cells suspended in the plasma just asthey are in the circulation. When blood is collected with ananticoagulant, the cells may be separated by centrifugation, andthe plasma used for testing. Blood collected in additive tubes(anticoagulant or clot activator tubes) must be mixed by gentlyinverting the tube several times to ensure even distribution of theadditive in the specimen (see table on page 14 for number ofinversions).

Please be aware that after centrifugation the entire initial volumeof a filled specimen collection tube will not be available forlaboratory tests that use serum or plasma. Refer to yourinstitutions minimum test volume requirements. Typically theamount of serum or plasma available for testing is less than 50%of the total volume of blood drawn.

Due to concerns of insufficient serum or plasma available for testing, many institutions discourage theuse of pedi bullets obtained from a heelstick or fingerstick. Also, these samples may be associatedwith greater degrees of hemolysis, which may interfere with laboratory testing.

Plasma (contains fibrinogen)

White blood cells & platelets (buffy coat)

Red blood cells

Clot Activator TubeWith Gel Separator

Anticoagulant Tube

Serum (minus most clotting elements)

Gel separator

Clot (blood cells in fibrin clot)

Serum (minus most clotting elements)

Clot TubeWithout Gel Separator

Clot (blood cells in fibrin clot)

Orientation of blood componentsfollowing centrifugation


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8 So Youre Going to Collect a Blood Specimen: An Introduction to Phlebotomy

Some nonroutine specimens may require special handling at the time of specimen acquisition.You should confirm with your supervisor which specimens require special handling.

For example:

Specimens for the testing of cold agglutinins or cryoglobulins must be kept warm (37C).

Specimens for the testing of blood gases, ammonia, and lactic acid must be chilled in ice water.

Specimens for the testing of bilirubin and certain vitamins must be wrapped in foil to preventexposure to light. If available, amber microcollection devices should be used for bilirubin specimensfrom newborns.

Some specimens may require immediate centrifugation and processing (eg, organic or amino acidsanalysis, unfractionated heparin measurement). The phlebotomist should confirm with the laboratorythat processing is available prior to collecting these samples.

Blood Collection Equipment

Blood collection systems

The evacuated tube system is the most frequently used equipment when performing venipuncture.This system consists of a double-pointed needle, an adapter to hold the needle and the collection tube,and a variety of color-coded evacuated collection tubes. Appropriate needles for blood collection areavailable in gauges from 20 to 23; however, the most common needle used is 21 gauge. The larger thegauge, the smaller the needle size. The needle adapters (holders) also come in a variety of sizes toaccommodate different sized collection tubes. Alternately, a butterfly needle (winged set) may beused, as appropriate.

The evacuated collection tubes are plastic (rarely glass). Their color code is based on their contentseither no additive or the type of additive they contain. The evacuated tubes have a label indicating thetype of additive they contain (such as anticoagulant or clot activator), the draw volume, and theexpiration date. These tubes fill automatically to a determined volume based on the amount of vacuum that is present in the tube. Evacuated collection tubes are sterile.

Always check the expiration date of the evacuated collection tube and other supplies prior to use.The expiration date refers to the last date the tube may be used for collection.

There are many new safety devices available for the evacuated tube collection system. Some use needleshields or self-blunting needles. Others use adapters that act as the safety shield for the used needle.The OSHA Bloodborne Pathogens Standard prohibits contaminated needles and other contaminatedsharps from being bent, recapped, or removed, unless the employer demonstrates that no alternativeis feasible or that such action is required by a specific medical or dental procedure.


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Shown prior to activation ofretractable safety device

Butterfly needles

Butterfly needles historically have accounted for a highly disproportionate share of needlestickinjuries because they have a tendency for one end to curl/recoil and stick the individual disposing

of the needle. These injuries can be reduced by the following: Always use a safety-engineered butterfly needle, which has been designedto reduce needlestick injuries.

Activate the safety device immediately upon removal of the needle fromthe patient.

Do not disassemble the tube holder from the needle assembly beforedisposal in a sharps container.

Limit the use of butterfly needles to special situations, such as patients with veins that are difficult to access with a straight needle.

Stretch out the butterfly tubing when removing it from the package to reduce recoil.

During disposal, be sure to stabilize the butterfly tubing, holding the end with the needle by theplastic needle support, to reduce the likelihood of having the needle flip back and stab you.

Replace sharps containers, as appropriate, so that all items intended for disposal can be safely placedin the container. Containers must never be overfilled and must be replaced when contents reach theindicated fill line. Puncture-resistant sharps containers must meet the requirements of national orlocal regulations.

Additives

Additive tubes contain anticoagulants, clotting activators, or both, with or without separator gel.

Anticoagulants are substances that prevent blood from clotting. Clot activators are substances(eg, glass, silica, thrombin) that promote clot formation.

There are many different kinds of anticoagulants used in evacuated tubes. They can be in liquidor dry form, and may be difficult to see in the tube. The correct anticoagulant must be used for thespecific test procedure to be performed (see the following). Using the incorrect evacuated tube oranticoagulant type is a cause for specimen rejection by the laboratory. Blood collected with oneanticoagulant may be suitable for one test or group of tests, but not for others.


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10 So Youre Going to Collect a Blood Specimen: An Introduction to Phlebotomy

Anticoagulants used in blood collection tubes

Collection tubes used for blood samples are color coded. The color of the stopper indicates whichtype of tube it is (see table on page 14). Since color standards may change, it is essential to check the

tube label as well.The anticoagulants most frequently used are:

EDTA. This anticoagulant is used primarily whenperforming complete blood cell counts (CBC).There also are other applications, such asdetermining red cell folate, blood lead, andhemoglobin A1c levels; monitoringimmunosuppressant drugs (eg, tacrolimus);and blood typing.

Sodium citrate. This anticoagulant is usedprimarily when performing coagulation studies,eg, prothrombin time (PT).

Heparin. This anticoagulant is used for a varietyof routine and specialized tests. Note: Tubescontaining heparin may contain either sodiumheparin or lithium heparin. In general, lithiumheparin is used for chemistry tests. However, alithium heparin tube must never be used todetermine a patients blood lithium or heparinlevel. Lithium heparin tubes must not be used whensodium heparin is indicated. Sodium heparin isused for specimens requiring the use of viablelymphocytes, such as HLA testing. A sodiumheparin tube must never be used to determine apatients blood sodium or heparin level. Thespecific type of heparin will be noted on the tubelabelread the label!

Fluoride-oxalate. This anticoagulant is usedprimarily for glucose and alcohol determinations.Enzymes, which may change glucose or alcoholconcentrations, are inhibited by the fluoride in thetube, and clotting is prevented by the oxalate.

Important tips to remember

To confirm the patients identity prior tocollecting any blood specimen, two uniquepatient identifiers should be used, such aspatient name, date of birth, medical recordnumber, or social security number.

The vacuum in the collection tube allowsthe correct amount of blood to enter thetube. Do not underfill (short draw) or

overfill additive tubes because this cancause erroneous test results and is a causeof specimen rejection by the laboratory.Never transfer blood from one tube toanother blood collection tube, even if ithas the same color stopper. This also is acause of specimen rejection by thelaboratory.

If your facility is located at a high altitude,the vacuum in the tube may be decreased.Extra care may be needed to ensure that

tubes are properly filled (consult yoursupervisor). Blood collected in tubes containing an

additive must be promptly and thoroughlymixed. Do not shake the tube. Mix bygently inverting the tube so that theadditive is thoroughly mixed with theblood (see table on page 14 for numberof inversions). If the blood and theanticoagulant are not thoroughly mixed,a partial clot may form and seriouslyinterfere with the test results. One of themost common preanalytic errors isinadequate mixing.


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The blood collection tray

A well-equipped, organized, blood collection tray is necessary for successful blood collection.

The blood collection tray must be kept clean and neat at all times. The tray should be checkedfrequently and decontaminated as needed with a 10% bleach solution or other decontaminatingsolution used by your institution. Supplies should be replenished as needed.

A typical tray should contain at least the following:

Disposable, properly fitted gloves

Packaged alcohol swabs or pads

Chlorhexidine gluconate/alcohol pads

Blood culture prep kits

Gauze pads (2" 2")

Adhesive tape or bandages

Permanent ink marking pen

Safety needle devices, includingblood tube holders and sterileneedles or butterfly needles

Blood collection tubes

Glass slides Microcollection tubes

Capillary tubes, if required

Capillary tube sealer, if required

Retractable, sterile blood lancet devices

Tourniquets(Note: Single-use, disposable, preferably latex-free tourniquets are becoming the standard of care.At a minimum, tourniquets must be discarded immediately when contaminated with blood or body

fluids, or if contamination is suspected.) Sterile syringes and safety needles

Puncture-resistant sharps container

Bar code reader/printer, as applicable

Preprinted labels may be included, if computerized order entry is used and the hospital has acentralized phlebotomy team. Labels should be appropriately separated by patient and location,and identification should be confirmed prior to the blood draw.

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