Order of Draw in Phlebotomy: Why It Matters
In laboratory medicine, accuracy begins at the point of specimen collection. One of the most important practices in phlebotomy is adhering to the Order of Draw—the standardized sequence in which blood collection tubes are filled during venipuncture.
The order of draw is designed to prevent additive carryover, a phenomenon in which additives from one collection tube contaminate the next tube collected. Even small amounts of contamination can alter test results, potentially affecting patient diagnosis and treatment decisions. By following the correct sequence, healthcare professionals help ensure specimen integrity, diagnostic accuracy, and patient safety.
Why the Order of Draw Is Important
Following the correct order of draw is more than a procedural requirement—it is a critical quality assurance measure.
1. Ensures Accurate Test Results
Each collection tube contains specific additives designed for particular laboratory tests. If additives are carried over into subsequent tubes, they can interfere with test results, leading to inaccurate findings.
2. Minimizes Specimen Contamination
Collecting tubes in the correct sequence reduces the risk of chemical contamination between specimens and preserves sample quality before laboratory analysis.
3. Promotes Standardization
The order of draw provides a globally recognized standard that supports consistency in specimen collection practices across healthcare facilities.
4. Improves Patient Care
Accurate specimens reduce the likelihood of rejected samples and repeat collections, minimizing patient discomfort and ensuring timely clinical decisions.
Recommended Order of Draw (CLSI Guidelines)
According to the Clinical and Laboratory Standards Institute (CLSI), the recommended order of draw for venous blood collection is:
1. Blood Culture Bottles or Tubes
Purpose: Detection of bloodstream infections and sepsis.
Blood cultures are collected first to maintain sterility and reduce the risk of contamination.
2. Light Blue Tube (Sodium Citrate)
Purpose: Coagulation testing, including PT/INR, aPTT, D-dimer, and other coagulation studies.
These tubes must be filled correctly to maintain the required blood-to-additive ratio.
3. Serum Tubes (Red, Gold, or Tiger-Top SST)
Purpose: Chemistry, serology, immunology, and certain therapeutic drug monitoring tests.
These tubes contain either no anticoagulant, a clot activator, or a serum separator gel.
4. Green Tube (Heparin)
Purpose: Chemistry testing, plasma determinations, and certain STAT laboratory tests.
Contains lithium heparin, sodium heparin, or ammonium heparin as an anticoagulant.
5. Lavender, Pink, or White Tube (EDTA)
Purpose: Hematology testing, complete blood counts (CBC), blood bank testing, and molecular diagnostics.
EDTA preserves cellular morphology and prevents clotting.
6. Gray Tube (Sodium Fluoride/Potassium Oxalate)
Purpose: Glucose, lactate, and blood alcohol testing.
These additives help preserve glucose levels by inhibiting glycolysis.
Best Practice: Proper Tube Mixing
After collection, tubes containing additives should be gently inverted according to the manufacturer's recommendations—typically 5 to 10 inversions, depending on the tube type. Vigorous shaking should be avoided, as it can cause hemolysis and compromise specimen quality.
Conclusion
Mastering the order of draw is a fundamental skill for every phlebotomist and laboratory professional. By following established CLSI guidelines, healthcare workers help preserve specimen integrity, ensure accurate laboratory results, and contribute to safer, more effective patient care.
Remember: a high-quality laboratory result begins with a high-quality specimen.
Technical note: Some laboratories also include additional tube types (such as royal blue, yellow ACD, tan, or white/PPT tubes) depending on the tests being performed. The sequence above represents the standard order most commonly used in routine venous blood collection.