From venipuncture to analysis results: what matters most for achieving quality samples and results?
What is the aim of blood collection? To achieve the best and most sample quality, which may then have a significant impact, for example, on diagnoses or therapy choices, impacting the life and health of the person concerned.
To achieve best possible analysis results, and thus the desired reliable diagnoses, leading to satisfied patients and ultimately reduced pressure on frontline staff due to erroneous sample material, it is essential to consider the entire process holistically. Every part of the value chain from the evaluation of the vein and selection of products, up until processing in the laboratory, can influence sample quality.
This means that a wide range of factors must be considered to ensure best practice in evacuated blood collection, so let us first discuss what ideally happens before the blood collection and what happens once the sample tubes have been filled.
Patient-centered
The blood collection value chain begins with the patient. From the moment of initially meeting the patient, the procedure starts. It is essential to create an atmosphere of calm before even beginning to evaluate veins, to ensure any anxiety or stress for the patient is prevented or minimized.
Stress does not just have a negative effect on the veins, as it leads to a spike in blood pressure, which can narrow the veins, it can also influence the blood parameters. When meeting a patient for blood collection, the window of time available to create an atmosphere of calm is small, so paying attention to appearance is a good way to create a feeling of trust and professionalism.
As the saying goes, first impressions count, so presenting with cleanliness, hygiene, and confidence is an opportunity that should not be wasted. Whilst meeting the patient, it should also be established if the patient has fulfilled any dietary restrictions, such as fasting, prior to the procedure and to make a note of this, should the patient not have fasted. This can have an influence on some parameters.
Another influential factor is ensuring the patient’s ID, either verbally and in written form, or if available electronically, by scanning a barcode on the patient’s wristband. Failing to ensure correct identification can have serious consequences in case of mixed identity, by prescribing an incorrect therapy which in the worst case may even be fatal. This step needs to be taken very seriously.
Hand hygiene
Once satisfied that patient and patient’s order are aligned, the patient is sitting or lying comfortable, and all the required products are within reach, then a puncture site is to be selected. To prevent any cross-contamination, proper hand hygiene must be performed first, by washing or sanitizing and disposable gloves should be worn during the procedure. Studies indicate that poor hygiene between patients and handling equipment is a significant cause of contamination [1]
Adapting to vein conditions
A comprehensive check should be made of the patient’s veins to ensure the best conditions for the venipuncture. It should not be underestimated, what an effect the choice of an unsuitable vein can have. Choose a vein that does not feel hard, has good blood flow and that does not divert or roll.
For evaluation purposes, a near infrared vein visualization device may be used, which is particularly helpful in making the right choice of needle size. If too small a diameter is selected for the conditions, for example, it may cause hemolysis [2] .
When there is a good understanding of the patient’s veins, an appropriate product can be selected. If a winged blood collection set has been chosen as the most appropriate product, it is essential to note that the air in the tubing of the set may cause the first tube to underfill, and it is recommendable to use a discard tube first to prevent an incorrect blood to additive ratio in the first tube, which could influence the analysis results, as described in CLSI PRE04 1st Edition [3].
Too much or too little blood for the amount of additive can have a negative effect on accurate test results. Incorrect fill volume is especially critical for coagulation tubes, which is why some manufacturers print a fill mark indicating + / - 10% of the nominal filling volume. It is highly recommended that sodium citrate coagulation tubes filled to below 90% of the fill volume be rejected [4].
Tourniquet application
At this point a tourniquet is applied, paying attention to the correct amount of pressure, no higher than 40mmHg2, which should feel comfortable whilst exerting a sufficient amount of pressure, meaning just enough to make the veins more prominent, any higher and the arterial blood flow may be blocked, resulting in failed or erroneous venipuncture.
If veins are not immediately visible after applying the tourniquet, the patient can be asked to make a fist, but should not be asked to pump, as this muscle movement can also influence some parameters.
As there may be possible microorganisms or contaminates on the patient’s skin, the puncture site must be suitably disinfected before inserting the needle. To ensure the skin is fully decontaminated, the disinfectant should also be allowed to air dry before puncture. It’s important to remember that the tourniquet must not be applied for over a minute, and should be loosened and then reapplied, should this time limit be exceeded.
Order of draw
Finally, the blood collection procedure is carried out, taking samples as required in the requested tubes according to the recommended order of draw, referring to CLSI GP41, 7th edition [5] as well as considering protocols in your own facility. Adhering to the order of draw makes a considerable contribution to sample quality, ensuring that the additives of the previous tube do not carry over into subsequent tubes, causing interference and ultimately erroneous results.
Handling of tubes
Once samples are collected, this is by no means the end of the value chain. The specimen tubes must be handled correctly to ensure analytes remain in an optimal condition. Tubes are gently inverted immediately on filling according to additive and instructions.
Shaking too vigorously can lead to rupture of the blood cells, possibly rendering the sample hemolytic and risking being rejected in the laboratory or if processed, incorrect results due to increased concentration of some analytes. Scientific literature suggests that hemolysis is one of the biggest causes of sample non-conformity in the laboratory [6].
Serum samples must be allowed to fully clot, and all tubes should be stored upright, including during transportation, as described in CLSI GP41, 7th edition. This ensures minimal interference caused by movement during the transportation, keeping samples intact, and reducing chances of hemolysis.
Centrifugation recommendations as recommended in the manufacturer’s instructions for use should be adhered to, ensuring the centrifugation time and recommended speeds for each tube type is observed. According to CLSI PRE046, plasma or fully clotted serum samples should be centrifuged within 2 hours, for the integrity of certain parameters, preventing any erroneous results [7].
Transport of samples
The next phase is transport into the laboratory, and the transportation path must be duly considered. The samples must be transported according to regulations for Category B biohazard samples, and care must be taken to prevent extremes of temperature, especially in hot summers and cold winters to ensure analytes remain stable until processing.
What other factors are important to consider?
Always be sure that the blood collection tubes you are using have not expired. If the shelf-life is exceeded, the vacuum of the tube could be insufficient or the additive may no longer be effective, impacting negatively on the blood sample quality.
Some parameters, for example bilirubin, are light sensitive and the tube may need to be protected against UV light by wrapping in protective foil or by using an amber tube [8].
[1] Kim JY, Ahn HJ, Lee EK, Chae HB. Anesthesiologist's hand hygiene and disinfection of reusable rubber tourniquet with alcohol swabs before intravascular cannulation. Korean J Anesthesiol. 2014 Dec;67(Suppl):S9-S10. doi: 10.4097/kjae.2014.67.S.S9. PMID: 25598925; PMCID: PMC4295999.
[2] WHO guidelines on drawing blood: best practices in phlebotomy, 2010, ISBN 978 92 4 159922 1
[3] CLSI PRE04 Handling, Transport, Processing and Storage of Blood Specimens for Routine Laboratory Examinations, 1st Edition., Clinical and Laboratory Standards Institute; August 2023
[4]Joint EFLM-COLABIOCLI Recommendation for venous blood sampling, v 1.1. June 2018, doi.org/10.1515/cclm-2018-0602
[5] CLSI GP41 Collection of Diagnostic Venous Blood Specimens, 7th Edition, April 2017
[6] Lippi, Giuseppe, von Meyer, Alexander, Cadamuro, Janne and Simundic, Ana-Maria. "Blood sample quality" Diagnosis, vol. 6, no. 1, 2019, pp. 25-31. https://doi.org/10.1515/dx-2018-0018
[7] CLSI PRE04 Handling, Transport, Processing and Storage of Blood Specimens for Routine Laboratory Examinations, 1st Edition., Clinical and Laboratory Standards Institute; August 2023
[8] Greiner Bio-One, Instructions for Use for VACUETTE® Evacuated Blood Collection System, Rev24, 05.2022, 980200
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