In clinical diagnostics, the accuracy of test results starts with proper blood sample collection. Among the variety of blood collection tubes, the Purple Top Blood Collection Tube stands out as a widely used and trusted option, especially for hematology and molecular testing. Its unique design and anticoagulant properties ensure blood samples remain suitable for a range of laboratory analyses.

What Is a Purple Top Blood Collection Tube?

A Purple Top Blood Collection Tube is a vacuum tube pre-coated with the anticoagulant EDTA (Ethylenediaminetetraacetic acid). EDTA prevents blood clotting by binding calcium ions, a vital component in the clotting process. This anticoagulation keeps the blood fluid, making it ideal for tests that require whole blood or plasma.

The purple color on the tube cap is a standardized code used worldwide to indicate the presence of EDTA inside the tube.

Why Are Purple Top Tubes Used?

• Prevents Clotting: The EDTA anticoagulant rapidly inhibits clot formation immediately after blood collection.

• Preserves Blood Cells: It maintains the shape and integrity of red blood cells, white blood cells, and platelets, crucial for accurate blood counts and morphology studies.

• Supports Molecular Tests: It stabilizes DNA and RNA, enabling genetic and infectious disease testing.

• Compatible With Automated Equipment: Samples collected in these tubes can be processed efficiently by hematology analyzers and molecular diagnostic machines.

Common Uses of Purple Top Tubes

• Complete Blood Count (CBC): Most routine hematology test using whole blood.

• Blood Smears: For microscopic examination of blood cells.

• Flow Cytometry: For immunophenotyping and detecting cell surface markers.

• Molecular Diagnostics: Including PCR-based assays and genetic tests.

• Blood Typing: Essential for transfusion compatibility tests.

Best Practices for Using Purple Top Tubes

• Fill to the Mark: Tubes should be filled to the recommended volume to keep the correct blood-to-EDTA ratio.

• Mix Gently: Immediately after collection, invert the tube gently 8 to 10 times to mix blood with the anticoagulant thoroughly.

• Avoid Vigorous Shaking: This prevents damage to blood cells and hemolysis.

• Process Promptly: Ideally, samples should be tested within 6 hours for optimal results.

• Store Properly: Keep tubes at room temperature away from extremes of heat or cold.

Advantages of Purple Top Tubes

• Highly effective anticoagulant with minimal impact on blood cell morphology.

• Widely accepted and standardized for hematology testing worldwide.

• Versatile, suitable for a broad range of hematological and molecular tests.

• Easy to identify by the purple cap, reducing collection errors.

• Available in various sizes to accommodate different volume requirements.

Limitations

• Not Suitable for Coagulation Testing: EDTA interferes with clotting assays like PT or aPTT.

• May Affect Certain Biochemical Tests: Such as calcium and potassium measurements.

• Improper filling (under or overfilling) may cause inaccurate results.

Conclusion

The Purple Top Blood Collection Tube remains a vital component in clinical laboratories. Its EDTA anticoagulant ensures that blood samples remain unclotted and cellularly intact, enabling accurate hematology and molecular test results. Adhering to proper collection and handling protocols maximizes its effectiveness, ultimately supporting better diagnosis and patient care.