Blood is a fluid carrying numerous critically important substances necessary for biological human life. Imbalances in the homeostatic levels of blood components can help to rule in or out a myriad of pathologic conditions. The relative ease of sampling using Evacuated Tube System (ETS) tubes with a variety of additives facilitates the analysis of blood samples. Venous blood sampling is a practice ubiquitous to virtually all areas of medicine.
Procedures for blood sample collection by prehospital providers are not as ubiquitous and the acceptance of such samples varies by receiving facility. Study data suggest samples collected by EMS personnel are of the same quality as those collected in the ED and prehospital blood collection has positive effects on patient outcomes.1 The most significant positive effect of prehospital blood collection is decreased patient throughput time. This, in turn, decreases patient distress and relieves some of the burden on the ED.1 EMS providers must be competent in the proper ETS blood collection techniques for the practice to expand and patients to reap the benefits. These techniques should be included in agency protocols.
The Evacuated Tube System
Phlebotomy for purposes of clinical analysis is typically done using multisample hypodermic needles varying in size from 21 to 23 gauge.2 Collection from Vascular Access Devices (VAD), or peripheral venous catheters, is an accepted practice but not preferred over direct phlebotomy.2 Intravenous insertion by EMS providers is typically done using angiocatheters ranging from 22 to 14 gauge, all of which are suitable for ETS sample collection.
Evacuated tubes are generally plastic — although some are glass — and are sealed by a rubber stopper at the top. Most have some form of additive, either in liquid form or sprayed into the tube and dried before the air is evacuated.3 The vacuum pressure assists in drawing blood into the tube easily and consistently.3 Some tubes may also contain a thixotropic gel which physically separates the plasma or serum from the heavier components of the sample upon centrifugation. A variety of additive tube types exist, but the two types likely to be carried in an EMS blood draw kit are anticoagulant tubes for plasma testing and clot activator tubes for serum testing.4
Proper Collection Techniques
ETS tubes should be held in an orientation that allows them to fill from the bottom toward the rubber stopper at the top.5 This may require that a patient laying supine on the stretcher have his or her arm draped off the stretcher to allow a downward orientation. If a tube is held inverted during filling, causing the blood to pool against the rubber stopper, small quantities of blood containing the additive from the tube may reflux into the patient’s circulation as the vacuum pressure is expended.5 Tubes should not be filled partially because a full tube can be used for additional tests.
For coagulation testing, the additive to blood ratio must be precise; expending all vacuum pressure consistently ensures this ratio.2 A tube that is inverted during filling can leave traces of the additive in blood remaining inside the sheathed needle. When the needle punctures an additional stopper, this additive can be carried into the next vial. Additive crossover is an undesired phenomenon in ETS blood collection that can be mitigated both by proper technique and order of draw.5
Latex or nitrile tourniquets used in typical multisample phlebotomy, and those used in pre-hospital venous cannulation, are identical and used for the same purpose. During standard IV insertion, the duration of time that the tourniquet is applied affects little aside from patient comfort. For the purposes of venous sampling, a tourniquet should not be left in place longer than one minute. Adverse effects of prolonged tourniquet time may affect test results after one minute.2 Additionally, fist pumping by patients during venous sampling is known to cause pseudohyperkalemia, which can be a particularly problematic false lab finding for patients.2 Patients who are candidates for ETS blood collection should be instructed to hold a fist without clenching or not to make one at all.2
The proper order of draw for multiple tube collections is set and standardized in the United States by the Clinical and Laboratory Standards Institute (CLSI). The order of draw is designed to minimize interference between the different additives in the tubes, hopefully resulting in consistent testing and accurate results.2 Tests done on plasma will result inaccurately — or be rejected altogether — if they arrive in the testing lab clotted.4 Serum tests which do not properly clot may also result inaccurately or be rejected.4 Following a standardized, proper order of draw minimizes the risk of these adverse events.
Competence in the procedure for venous blood sampling by providers who collect samples for analysis is critically important. Failure to comply with standard practices can cause erroneous results, potentially resulting in inappropriate treatment decisions .
A basic blood draw kit carried on an ambulance would most likely consist of the following, arranged in proper CLSI order of draw: a blue top, orange or red top, green top, and lavender top.2 A kit with these tubes would allow rapid processing of a comprehensive battery of coagulation labs, blood chemistries, and blood component counts.6 Some sample types must be centrifuged within certain time limits, so it may be inappropriate or unproductive to draw these samples on patients whose transport times will likely exceed these limits.
The following is a step-by-step procedural outline for venous sampling via ETS which could be followed by EMS providers in the field:
1. Don PPE and set up your equipment, including your IV catheter, IV start kit, ETS tube holder, tubes, IV lock and saline flush. Prepare your saline flush by attaching the lock and filling the tubing with saline, per agency protocol.
2. Place the tourniquet and identify a suitable vein. Remove the tourniquet if necessary.
3. Use antiseptic wipe to prepare the venipuncture site, then place the tourniquet and prepare the IV needle/catheter. Using proper aseptic technique, insert the IV catheter into the vein. Ensure that the tourniquet remains in place for no more than one minute before beginning to fill tubes.
4. Once the catheter is in place, attach the tube holder to the IV catheter.
5. Fill the tubes in order of draw, holding the tubes in an orientation to fill from bottom to top. Gently invert the tubes according to manufacturer recommendations to ensure complete mixing with the additives. Do not shake.
6. When the last tube is full, release the tourniquet, manually occlude the vein to prevent loss of blood, remove the ETS tube holder, and attach the saline lock. Flush the catheter, secure the IV and apply a dressing following your agency’s IV insertion protocol.
7. Label each tube with identifying information as required by the receiving facility.
As prehospital providers, EMS personnel can be better partners with our receiving facilities by providing competent care that anticipates needs beyond the ED doors. Establishing protocols for venous blood collection is a simple, effective way to reduce throughput and improve patient satisfaction. Medical directors considering protocols for venous blood sample collection may need to consult with their receiving facilities for specific recommendations on tube selection, labeling and collection protocols.
- Harrison G, Speroni KG, Dugan L, et al. A comparison of the quality of blood specimens drawn in the field by ems versus specimens obtained in the emergency department. Journal of Emergency Nursing. 2010;36(1), 16-20.
- CLSI: GP-41 Collection of Diagnostic Venous Blood Specimens – Seventh Edition. Clinical and Laboratory Standards Institute: Wayne, PA, 2017.
- CLSI: GP39-A6 Tubes and Additives for Venous and Capillary Blood Specimen Collection; Approved Standard–Sixth Edition. Clinical and Laboratory Standards Institute: Wayne, PA, 2010.
- Kiechle, F. L., MD, PhD. So You’re Going to Collect a Blood Specimen, An Introduction to Phlebotomy (14th ed.). College of American Pathologists Press. Northfield, Illinois, 2013.
- McCall, R. E., & Tankersley, C. M.: Phlebotomy essentials (6th ed.). Wolters Kluwer: Philadelphia, PA, 2016.
- Ernst D. J.: Applied phlebotomy. Lippincott Williams & Wilkins: Baltimore, MD., 2005.