Importance of blood sample collection procedure & sample handling
Total testing process comprises of pre-analytical, analytical and post-analytical phases. With increased laboratory instrumentation & automation and technology advancements, the accuracy of results in laboratory (or analytical) phase has become smaller concern. However, the pre-analytical stage, the way the blood test sample is collected, pre-processed, stored and transported is an important step, which is still neglected. According to some studies, pre-analytical phase accounts for almost 68.2% of the errors in total testing process, much higher than analytical phase with 13.3% errors. As anyone might conclude, these errors result in higher healthcare costs due to avoidable investigations & inferior patient care.
Of all the errors occurring during all the stages, errors in pre-analytical stage are the hardest to detect and may go un-identified many a times. Therefore, prevention of these errors at the pre-analytical stage is the way forward. The errors in pre-analytical stage can happen either in sample collection, handling, transport, storage, pre-processing, or even due to variables influenced by patient.
Following are the typical errors which may occur during pre-analytical stage:
1. Physiological state of patient
The blood or urine report parameters are highly impacted by the various decisions entirely in control of patients. For many of the blood tests, it is preferred that patient should have fasted and rested before giving the sample. Diet, medication, dehydration, drinking / smoking, posture and exercise may have undesired impact on the results of a blood test.
2. Errors during sample collection (including phlebotomy)
Most of the errors in pre-analytical phase occur during specimen collection. These errors are because of incorrectly labeled samples, insufficient sample for testing, in-appropriate blood to anti-coagulant ratio, microbiological contamination of the venipuncture site (due to non-usage of gloves), or because of other sample quality issue due to incorrect phlebotomy procedures. Incorrect phlebotomy procedures may include, in-appropriate needle gauge size, wrong order of draw in various tubes (Gold top followed by Lavender top, & then Grey top), or a forced draw of blood. According to some studies, almost 30% of the errors occur at phlebotomy stage. Phlebotomist must avoid too vigorous shaking of sample tubes to prevent chances of haemolysis. Many manufacturers (like BD) specify the ideal ways & methods for blood sample and anti-coagulant mixing by gently inverting the tubes a number of times, as specified by the manufacturer.
All these seeming harmless errors can lead to in-accurate results or undesired state of blood samples (like haemolysis, lipemia or icterus). These states cause a variety of anylate interferences (or inaccurate results), as explained below. Technology has enabled measurement of Indices for measurement of these states. We will discuss about haemolysis and Lipemic samples, in detail, later.
3. Sample Handling: Transport, storage and pre-processing
Each of these samples needs to be transported at required temperature levels (frozen, refrigerated or room temperature as per the sample requirement) and processed at defined centrifugation speed levels / time. Non-compliance with any of these procedures may lead to deterioration of samples (like Haemolysis) and in-accurate laboratory results.
After the sample is collected in tubes, the tubes are placed vertically in the specially designed ice-boxes. These ice-box have been specially prepared for blood sample transport, which provide ideal transport temperature ranges, shock resistance, and providing some airspace to avoid direct contact of tubes with ice packs. This box is then kept in specially designed EPS (Expanded Styrofoam) casings with coolant gel packs for transport to Pre-Analytical centers, where they are pre-processed (especially centrifugations) before movement to testing laboratories. Longer transit times have specially designed packaging for maintaining temperatures within the permissible range. Curill’s pre-analytical technicians and phlebotomists have regular trainings and Standard Operating Procedures (SOPs) to ensure compliances for each of these steps.
Impact of improper handling of blood sample
As highlighted above, improper blood sample handling may lead to Haemolysis and Lipemia, which are the main causes for samples rejection. Lets understand a bit more about them and how they impact the results.
Haemolysis is caused by release of haemoglobin in serum or plasma due to rupture of RBCs. Visible haemolysis is concentration of free haemoglobin in greater than 100 mg/L. Though haemolysis impacts a variety of blood parameters (including but not limited to ALP, Chloride, HDL Cholesterol, glucose, magnesium, tri-glycerides, UIBC), studies have particularly indicated its major impact on Potassium & Bilirubin in case of moderate haemolysis (Hb > 1 g /L), and on ALT (SGPT), cholesterol & GGT in severely haemolyzed samples (>2.5 g / L). AST (SGOT) or LDH (Lactate Dehydrogenase) are impacted even at clinically insignificant levels of haemolysis (2,3). Laboratories employ a variety of methods, ranging from special visual check by trained biochemistry professionals to detection of plasma or serum free haemoglobin levels by optical sensors.
Lipemia is the turbidity of blood samples caused by excessive concentration levels of lipoproteins particles (mainly Chylomicrons). Most important cause of lipemia is not sufficient time given to blood withdrawal after a meal. Most laboratories employ visual methods to segregate lipemic samples. However, very high level of Triglycerides in the blood sample is a non-visual indicator of Lipemic sample (though high triglycerides is not a conclusive evidence, as some blood samples may genuinely be having high TG levels). Lipemia, in general is lesser cause of concern than a haemolyzed sample, however, it may impact electrophoresis based methods (SPEP), immunoassays (like IgG, IgM testing), and spectrophotometric methods (like AST, ALT, glucose). Though there are methods like Utra-centrifugation for separation of the turbidity, it is better for the patient to follow 12 hrs fasting before blood sample collection.
In short, pre-analytical phase is a very important and often ignored stage of pathological testing. Each and every member of this process, from patient to phlebotomist or lab technician, plays a very important role in minimizing these errors. At Curill, we understand and take our responsibility very seriously. We follow the optimal sampling and sample handling procedures to ensure quality results for all our customers.