In the medical laboratory, precision starts at the point of collection. One of the most critical steps in ensuring diagnostic accuracy is adhering to the Order of Draw.

The order of draw is the standardized sequence in which blood collection tubes must be filled during venipuncture. This sequence prevents additive carryover—where chemicals from one tube contaminate another—and ensures the most accurate test results possible. Laboratories rely on the consistency of this process to maintain sample integrity and patient safety.

Why the Order of Draw Is Essential

Following the correct sequence is not just a best practice; it is a clinical necessity for several reasons:

1. Accurate Results: Additives serve unique purposes—preservation, clot activation, or anticoagulation. Unintentional mixing can alter electrolytes or clotting times.

2. Reduced Contamination: Incorrect sequencing causes chemical interference, compromising the quality of the specimen before it even reaches the analyzer.

3. Standardization: A universal method keeps phlebotomy practices consistent and safe across all healthcare settings globally.

4. Better Patient Experience: High accuracy means fewer repeat draws, reducing patient discomfort and increasing trust in the facility.

The Correct Order of Draw (CLSI Standard)

To ensure the best outcomes, follow this officially recognized sequence according to the Clinical and Laboratory Standards Institute (CLSI):

1. Blood Culture Bottles (Yellow/BC Sets)

Purpose: Used to detect infections in the bloodstream. These are collected first to maintain sterility.

2. Light Blue Tube (Sodium Citrate)

Used for: Coagulation studies (PT, PTT). Precise filling is vital here to maintain the 9:1 blood-to-additive ratio.

3. Red or Gold/SST Tube (Serum Separator)

Used for: Chemistry, serology, and immunology tests. These contain clot activators or no additives.

4. Green Tube (Heparin)

Used for: STAT chemistries and electrolytes. Contains Lithium or Sodium Heparin.

5. Lavender or Pink Tube (EDTA)

Used for: CBC (Hematology) and blood bank tests. EDTA is a strong anticoagulant that preserves cell morphology.

6. Gray Tube (Potassium Oxalate/Sodium Fluoride)

Used for: Glucose and lactate testing. The additive inhibits glycolysis (the breakdown of sugar).

Pro-Tip: Always invert your tubes gently the recommended number of times (usually 5–10) immediately after collection to ensure the blood and additives mix thoroughly without causing hemolysis.

Mastering the order of draw is a hallmark of a professional phlebotomist. By following these standards, you protect the integrity of the diagnostic process and contribute to better patient care.