**Specimen Processing
This lesson focuses on the processing and handling of hematology and coagulation specimens, critical for accurate laboratory results. You will learn about the different blood collection tubes, proper techniques for processing, and the factors that can affect test results in these crucial areas of the lab.
Learning Objectives
- Identify and differentiate the various blood collection tubes used for hematology and coagulation testing.
- Describe the proper procedures for specimen centrifugation and storage for hematology and coagulation.
- Explain the common pre-analytical errors that can impact hematology and coagulation test results.
- Recognize the importance of quality control in specimen processing and handling for accurate results.
Text-to-Speech
Listen to the lesson content
Lesson Content
Hematology Tubes and Testing
Hematology testing primarily uses lavender-top tubes (containing EDTA anticoagulant). EDTA prevents clotting and preserves cell morphology. Common tests include Complete Blood Count (CBC), which measures red blood cells (RBCs), white blood cells (WBCs), platelets, hemoglobin, and hematocrit. Other tests include erythrocyte sedimentation rate (ESR), which can be run using the same EDTA tube. When collecting blood for hematology, ensure the tube is properly filled to the designated fill line. Underfilling can lead to inaccurate results due to the anticoagulant-to-blood ratio. Overfilling is less likely but can also interfere with results. Always gently invert the tube 8-10 times immediately after collection to ensure proper mixing of the blood and anticoagulant, preventing clot formation.
Coagulation Tubes and Testing
Coagulation testing relies on light-blue-top tubes containing sodium citrate anticoagulant. The citrate binds calcium, preventing clotting. Coagulation tests, such as Prothrombin Time (PT), Partial Thromboplastin Time (PTT), and Fibrinogen, assess the blood's ability to clot. These tubes require a specific fill volume to ensure the correct anticoagulant-to-blood ratio (usually 9:1). Underfilling is a significant source of error and can falsely prolong clotting times. Overfilling is uncommon but can lead to falsely short clotting times. Like hematology tubes, immediately invert the light-blue-top tube 3-4 times after collection to mix the anticoagulant and blood effectively. This must be done gently to avoid hemolysis. If multiple tubes are drawn, the light-blue top tube should always be drawn first (if only a coag tube and a hematology tube are required) to minimize the chance of platelet contamination from other tubes. If the patient has a hematocrit greater than 55%, the amount of citrate anticoagulant must be adjusted. Consult your lab's protocol.
Centrifugation and Storage
After collection and proper mixing, specimens need to be processed according to the lab’s Standard Operating Procedures (SOPs).
- Centrifugation: Hematology tubes typically do not require centrifugation immediately unless testing requires it. Coagulation tubes are always centrifuged to separate the plasma from the cells. Centrifuge according to the lab's instructions (usually for 10-15 minutes at a specific speed). Balance the tubes carefully in the centrifuge to avoid damage and inaccurate results.
- Storage: Most hematology tests are stable at room temperature for several hours. Coagulation tests are more time-sensitive. Plasma for coagulation testing should be separated from the cells and either tested immediately or stored properly (usually frozen at -20°C or colder) if the test cannot be run within the required timeframe, as specified by laboratory SOPs. Follow lab-specific protocols for storage times and temperatures to maintain sample integrity. Always label specimens with the date, time, and your initials if you are separating and/or storing them.
Pre-Analytical Errors and Quality Control
Pre-analytical errors are those that occur before testing and are the most common source of errors in the laboratory. Common errors include:
- Incorrect Tube Selection: Using the wrong tube for a test will invalidate the results.
- Improper Fill Volume: Both underfilling and overfilling can affect test results.
- Clotting: Clots in hematology or coagulation samples render them unusable. This can occur due to inadequate mixing, difficult draws, or delayed processing.
- Hemolysis: The breakdown of red blood cells, which can interfere with some tests. This can occur from vigorous shaking, small needle gauge, or difficulties with the venipuncture.
- Delayed Processing: Delays can affect the stability of some analytes, leading to inaccurate results.
Quality control (QC) is crucial for ensuring accurate results. QC procedures, such as running control samples, help to monitor the accuracy and precision of testing. Always check the lab's QC protocols and follow them meticulously before processing specimens.
Deep Dive
Explore advanced insights, examples, and bonus exercises to deepen understanding.
Phlebotomy: Advanced Specimen Processing & Handling - Day 4 (Intermediate)
Deep Dive: Beyond the Basics
Let's delve deeper into the nuances of specimen processing and handling, focusing on the subtle yet critical aspects that can dramatically influence test accuracy. We'll examine the physics and chemistry behind some key processes, and explore the complexities of handling specimens from diverse patient populations. Understanding these concepts will help you troubleshoot issues and consistently deliver high-quality results.
1. Centrifugation Considerations: Beyond RPMs
While RPM (Revolutions Per Minute) is crucial, Relative Centrifugal Force (RCF), measured in 'g' (gravity units), is the more accurate indicator of separation power. This force is affected by the rotor radius. A larger radius, even at the same RPM, generates a higher RCF. Incorrect RCF can lead to inadequate separation (e.g., incomplete clot formation in coagulation tubes) or damage to blood cells (hemolysis). Always refer to your laboratory's SOP for the specific g-force required for each test, rather than solely relying on RPM.
Consider the impact of temperature during centrifugation. Some analytes are temperature-sensitive. Refrigerated centrifuges are essential for specimens like those used for certain coagulation tests, where factor degradation can occur at higher temperatures. Be aware of temperature fluctuations within the centrifuge and how these can vary across different models.
2. Anticoagulant Actions: A Chemical Perspective
Understanding how anticoagulants work at the molecular level allows for a deeper understanding of potential pre-analytical errors. For example:
- EDTA (Ethylenediaminetetraacetic acid): EDTA chelates calcium ions, preventing the coagulation cascade. However, excessive EDTA can cause cellular changes (e.g., shrinking of red blood cells), especially if the blood-to-anticoagulant ratio is incorrect.
- Citrate (Sodium Citrate): Citrate also chelates calcium ions, but in a reversible manner, allowing for coagulation testing. The citrate concentration (e.g., 3.2% or 3.8%) must be precise. Underfilling citrate tubes will lead to inaccurate results because the ratio of citrate to blood is off, leading to falsely prolonged clotting times. Overfilling can dilute the sample.
- Heparin: Heparin enhances the activity of antithrombin, which inhibits several coagulation factors. Different forms of heparin (e.g., lithium heparin, sodium heparin) may be used depending on the test.
3. Special Populations: Neonates & Geriatrics
Processing specimens from neonates and geriatric patients presents unique challenges. Neonates often have smaller blood volumes and more fragile veins. Geriatric patients may have fragile veins, medications that affect coagulation, and may have limited mobility. When drawing from these populations, consider the following:
- Neonates: Microcollection techniques (e.g., capillary tubes) and heel sticks are often employed. Ensure proper order of draw to avoid contamination. Minimize blood volume collection to prevent iatrogenic anemia.
- Geriatrics: Gentle handling of veins, appropriate needle gauge, and meticulous site selection are crucial. Consider the patient's medications and potential impact on test results (e.g., anticoagulants, antiplatelet drugs). Post-phlebotomy care, including pressure application, is especially important to prevent hematoma.
Bonus Exercises
Exercise 1: Troubleshooting a Clotting Time
You receive a coagulation sample with a prolonged PT (Prothrombin Time) and a normal INR (International Normalized Ratio). The sample was drawn using a blue-top tube. List at least three possible pre-analytical errors that could be contributing to this result, and suggest how you would investigate each potential error.
Exercise 2: Calculating Centrifugal Force
A centrifuge has a rotor radius of 15 cm. The laboratory's SOP specifies a centrifugation speed of 3000 RPM for a certain test. Calculate the Relative Centrifugal Force (RCF) in 'g' units. (Hint: You can find online calculators for this). Then, research why knowing the RCF is superior to only knowing the RPM.
Real-World Connections
The principles of proper specimen processing extend far beyond the laboratory. Consider how these skills apply in these situations:
- Patient Safety: Accurate results directly impact diagnoses, treatment decisions, and patient safety. Any error you introduce in the pre-analytical phase has the potential to endanger a patient.
- Laboratory Efficiency: Proper specimen handling reduces the need for recollects, saving time, resources, and patient inconvenience.
- Legal & Ethical Considerations: Following proper protocols protects the laboratory and patient in the event of legal challenges. It is part of your professional responsibility.
- Interdepartmental Collaboration: Effective communication with nurses, doctors, and other laboratory staff concerning specimen requirements and issues.
Challenge Yourself
Research and prepare a short presentation (5-7 minutes) on the impact of pre-analytical errors on one specific hematology or coagulation test. Consider the following questions:
- What is the test and what is it used for?
- What are the most common pre-analytical errors that affect this test?
- How can these errors be prevented?
- What are the consequences of these errors for the patient?
Further Learning
Continue your learning journey by exploring these topics and resources:
- External Quality Control (EQC) and Proficiency Testing: Learn about how labs ensure their results match those of peers.
- Point-of-Care Testing (POCT): Research how this affects specimen handling and results interpretation.
- Laboratory Information Systems (LIS): Learn about how LIS systems track samples and flag potential errors.
- CLSI Guidelines: (Clinical and Laboratory Standards Institute). A primary source for standardized laboratory procedures.
- Online Journals: Search for articles on pre-analytical errors in the American Journal of Clinical Pathology or other related journals.
Interactive Exercises
Tube Identification Quiz
Examine a set of blood collection tubes. Identify each tube by color and the anticoagulant it contains. Then state the tests that each tube is typically used for. Consider the order of draw and its importance.
Specimen Processing Simulation
Simulate the processing of a hematology and coagulation specimen. Include proper mixing, centrifugation (if necessary), and storage protocols as outlined by a provided lab SOP. Document each step and the rationale behind it.
Error Scenario Analysis
Analyze several scenarios involving pre-analytical errors. For each scenario, identify the error, explain its potential impact on the test results, and describe the corrective action that should be taken.
QC Procedure Review
Review a set of lab QC data for a coagulation assay. Interpret the data to determine if the assay is within acceptable limits. If not, suggest potential troubleshooting steps.
Practical Application
Develop a mock laboratory protocol for processing hematology and coagulation specimens. Include tube selection, order of draw, mixing techniques, centrifugation parameters, storage requirements, and QC procedures. Include a troubleshooting section.
Key Takeaways
Correct tube selection is critical for accurate hematology and coagulation testing.
Proper mixing of blood with anticoagulants is essential to prevent clotting.
Centrifugation and storage must adhere to lab protocols to ensure specimen integrity.
Pre-analytical errors are the leading cause of inaccurate results, so careful attention to detail is vital.
Next Steps
Prepare for the next lesson on Point of Care Testing (POCT) and the roles and responsibilities of a phlebotomist in POCT environments, including quality control and patient safety.
Your Progress is Being Saved!
We're automatically tracking your progress. Sign up for free to keep your learning paths forever and unlock advanced features like detailed analytics and personalized recommendations.
Extended Learning Content
Extended Resources
Extended Resources
Additional learning materials and resources will be available here in future updates.