Chapter 16 Laboratory Specimens
General Principles of Specimen Collection
The following are general principles for all specimen collection:
• Identify the patient with two unique identifiers, such as name and date of birth. See institutional policy regarding which identifiers should be used.
• Prepare the site antiseptically.
• Observe standard precautions and hand hygiene.
• Label the specimen collection tubes and bottles at the patient’s bedside after specimens are collected as per institutional policy.
• Avoid drawing excessive amounts of blood, especially from critically ill patients. The volume of blood collected often exceeds the need and can contribute to anemia. Consider pediatric tubes for fragile veins or an anemic patient.1
Use the following procedures to prevent hemolysis of blood specimens1:
• Promptly transport the specimen to the laboratory.
• Use a properly sized syringe (no larger than 20 mL) to prevent excessive suction.
• If transferring blood from the syringe into blood collection tubes, allow the vacuum of the tubes to facilitate the transfer of the blood specimen. Do not exert pressure to force blood through the needle into the tubes. Use a needleless transfer device, if available, to decrease the risk of needlesticks and spray.
• Drawing blood specimens through a small needle or catheter can rupture the blood cells and potentially cause inaccurate results that require recollection of blood specimens.
• Gently invert the tube approximately five times to mix the blood specimen with any preservative that may be present in the tube.2 Do not invert tubes without additives to reduce the incidence of hemolysis.
• Release the tourniquet as the final tube is filling. See Chapter 10, Intravenous Therapy, for more information.
Hemolyzed specimens can occur in as many as 3.3% of all routine samples, nearly five times higher than other causes for unsuitable blood specimens.3 Hemolysis is less likely when blood is collected in evacuated tubes rather than with a syringe.2
Order of Specimen Tube Draws
Proper tube order prevents cross-contamination of preservatives that are found in specimen collection tubes. The Clinical and Laboratory Standards Institute (CLSI) indicates the order should be as follows4:
• Blood cultures: This minimizes potential contamination.
• Light blue: This tube contains sodium citrate, which removes calcium. This prevents contamination of the clot activator and interference with coagulation cascade.
• Red: This tube has no additive and is for the collection of serum.
• “Tiger” or Yellow: These serum separator tubes contain a polymer gel and clot activator in order to separate the serum with centrifuge.
• Green: This tube contains lithium heparin.
• Lavender: This tube contains ethylenediaminetetraacetic acid (EDTA), an anticoagulant additive that chelates calcium.
• Gray: This tube contains sodium fluoride and potassium oxalate anticoagulant to inhibit glycolysis.
Blood Collection Procedures
Venous Blood Samples
Use the following techniques to find a good site for venous access:
• Lower the extremity so that the site is below the level of the heart.
• Apply a warm compress to the area.
• Palpate for a vein using fingertips. Some large veins are deep and cannot be visualized but can be palpated. If available, use an ultrasound vein finder to assist in locating veins.
Once access is established, to obtain the best specimen follow these guidelines:
• Avoid having the patient repeatedly clench and unclench his or her fist when blood is being draw for potassium; making a single fist is acceptable. Fist exercises, with excessive tourniquet use, before venipuncture may cause an elevation of potassium as high as 1 mEq/L.1,5
• Limit the use of a tourniquet to no more than 2 minutes (1 minute is optimal) during specimen collection.
• Avoid using a site that is heavily scarred, is excessively swollen, has a hematoma, is on the affected side after a mastectomy, is an extremity affected by stroke or neurological injury, or has a fistula in the same extremity.
• Do not use a pulsating, thick-walled vessel (classic for an artery) or a cordlike, easily rolled vessel (classic for thrombosed vein) for blood specimen collection.
• Avoid drawing a blood specimen from a vein above the site of an infusing intravenous solution since this can lead to false results.
Venous Access Procedure
• Perform hand hygiene. Don clean examination gloves and prepare the site with available antiseptic.
• Palpate the site above the proposed needle entry point; do not touch the actual site.
• Stabilize the vein with the thumb of the nondominant hand.
• Draw the skin taut below the site to prevent the vein from moving when punctured.
• Insert the needle at a 30-degree angle with the bevel facing up (downward in small children). An angle steeper than this increases the risk of passing through the vein.
• Draw blood into specimen tubes in the order established by facility policy. See “Order of Specimen Tube Draws” which begins on page 167.
• Remove gloves, dispose of supplies, and perform hand hygiene.
Peripherally Inserted Central Catheter, Central Line, or Port
In preparing to collect blood specimens, it is important to review what laboratory tests have been ordered to ensure gathering of the appropriate supplies. It is important when using an established intravenous (IV) or central line for blood collection that the nurse clears the IV or central line from potential contamination from recently administered IV fluids or other medications. For additional information, see Chapter 10, Intravenous Therapy.
General principles for clearing the IV or central line include the following:
• Gather required supplies, such as the following:
• Inform the patient of the need to obtain blood specimens.
• Perform hand hygiene. Don clean examination gloves.
• Stop the infusion for at least 2 minutes prior to the blood specimen draw. If the central line has multiple lumens, stop all infusions and clamp the lumens not being used for the specimen collection.
• Aggressively cleanse the hub of the IV adaptor with an alcohol wipe or chlorhexadine.
• Flush the peripheral line or lumen being used with 10 mL of normal saline.
• Attach a 10-mL syringe and withdraw 8 to 10 mL of blood from the lumen and discard.
• Attach a 10-mL syringe and withdraw 10 mL of blood and transfer to the blood collection tubes until all specimens are collected.
• Flush the lumen with 10 mL of normal saline or heparin as per institutional protocol.
• Replace the hub of the IV adaptor used for the blood draw.
• Unclamp any lumens currently in use and clamped and resume all infusions.
• Label all blood collection tubes per institutional policy and send to the laboratory for processing.
Additional tips for specimen collection with a peripheral line or port:
• When using a peripheral line, slight manipulation of the catheter (pull back slightly on the catheter, move catheter from left to right) may be required to facilitate withdrawal of the blood.
• Do not use a peripheral line for blood specimen collection if there is a risk of compromising the integrity of the site when completed. Perform a venipuncture instead.
• Do not leave the tourniquet on for prolonged periods of time, especially if drawing a lactate or potassium level.
• Turn off IV infusion and discard an adequate amount of blood to ensure accuracy of the results.
• If collecting the blood specimen from a saline lock or unused port of a multiple lumen central line, flush with saline or heparin lock solution per institutional policy.
• If available, use needleless blood collection systems when collecting blood specimens from a peripheral IV line or central line to reduce the risk of needlestick and exposure to blood.
Arterial Puncture for Blood Gas Collection
General principles guiding collection of an arterial blood sample include the following:
• Gather the appropriate supplies. Inform the patient of the need to obtain the ABG specimen.
• Perform hand hygiene. Don clean examination gloves.
• Perform an Allen test. The modified Allen test is an option for the radial site to check the collateral ulnar circulation.4
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