In clinical laboratories and medical settings, the choice of blood collection tubes is critical for ensuring reliable and precise test results. One of the most commonly used tubes is the Purple Top Blood Collection Tube, recognized for its distinctive lavender or purple cap. This tube plays a vital role in blood sample collection, particularly for hematology and molecular diagnostics.

What is a Purple Top Blood Collection Tube?

The Purple Top Blood Collection Tube contains the anticoagulant Ethylenediaminetetraacetic acid (EDTA), usually in the form of a spray-dried or liquid coating inside the tube. EDTA works by binding calcium ions in the blood, which are essential for the clotting process. This action prevents the blood from coagulating, preserving the sample in a fluid state for various laboratory tests.

Why Use the Purple Top Tube?

• Prevents Blood Clotting: EDTA stops the clotting cascade immediately after blood collection, ensuring samples remain unclotted.

• Preserves Cellular Integrity: Maintains the morphology of red blood cells, white blood cells, and platelets, essential for accurate hematology analysis.

• Stabilizes Nucleic Acids: Ideal for molecular tests that require intact DNA or RNA.

• Compatible with Automated Instruments: Facilitates accurate readings on hematology analyzers.

Common Applications of the Purple Top Tube

• Complete Blood Count (CBC): The most frequent use, measuring various blood components like hemoglobin, hematocrit, and cell counts.

• Blood Smears: Used for preparing slides for microscopic examination of blood cells.

• Molecular Diagnostic Tests: Suitable for PCR and genetic testing, where nucleic acid stability is crucial.

• Blood Typing and Crossmatching: Essential in blood transfusion compatibility testing.

• Flow Cytometry and Other Specialized Tests: Often used in immunophenotyping and cell marker analysis.

Advantages of the Purple Top Blood Collection Tube

• Reliable Anticoagulation: Prevents clotting while preserving cells.

• Sample Stability: Maintains sample quality for several hours when stored properly.

• Widely Accepted Standard: The purple cap is universally recognized for EDTA tubes.

• Ease of Use: Available in various sizes and compatible with standard blood collection systems.

• Cost-Effective and Safe: Manufactured to meet stringent quality standards, ensuring safety for patients and laboratory staff.

Proper Handling and Usage Tips

1. Fill Volume: Always fill the tube to the recommended volume to maintain the correct blood-to-EDTA ratio.

2. Mixing: Immediately invert the tube gently 8-10 times after collection to ensure proper anticoagulant mixing.

3. Avoid Vigorous Shaking: Prevent hemolysis by avoiding rough handling.

4. Processing Time: For optimal results, process samples within 6 hours of collection.

5. Storage Conditions: Store at room temperature and avoid exposure to extreme temperatures.

Limitations and Considerations

• Not suitable for coagulation studies such as PT or aPTT, as EDTA removes calcium necessary for these tests.

• May interfere with assays measuring calcium and potassium.

• Underfilling or overfilling can impact the accuracy of test results.

Conclusion

The Purple Top Blood Collection Tube is a cornerstone of modern blood testing. Its ability to prevent clotting while preserving cellular detail makes it indispensable for hematology, molecular diagnostics, and many other critical tests. Understanding its proper use and limitations ensures accurate lab results and better patient care.

Whether in hospitals, diagnostic labs, or research facilities, the purple top tube remains a trusted and essential tool for blood collection.