Blood Collection Tube Colors Every Medical Assistant Should Know

Medical assistants who perform venipuncture play an important role in ensuring laboratory specimens are collected correctly the first time. One of the most important skills is understanding which blood collection tube color is used for which laboratory test. Selecting the wrong tube can result in specimen rejection, inaccurate laboratory results, delayed diagnosis, and unnecessary repeat blood draws.

While tube colors may vary slightly among manufacturers, the additive inside each tube determines how the specimen is processed and which laboratory tests can be performed.

This guide reviews the most common blood collection tube colors, their additives, and the tests medical assistants commonly encounter in clinical practice.

Why Do Blood Collection Tubes Have Different Colors?

Each blood collection tube is designed for a specific type of laboratory testing.

The additives inside the tube may:

• Prevent blood from clotting
• Promote clot formation
• Preserve blood cells
• Stabilize glucose levels
• Separate serum or plasma from blood cells

Selecting the correct tube is essential for obtaining accurate laboratory results and preventing specimen rejection.

Medical assistants who understand both tube colors and their additives help improve patient safety and laboratory quality.

 

Light Blue Tube

Additive

Sodium Citrate

Common Tests

Light blue tubes are primarily used for coagulation studies, including:

• Prothrombin Time (PT)
• International Normalized Ratio (INR)
• Activated Partial Thromboplastin Time (aPTT)
• Coagulation factor studies

Clinical Tip

Because coagulation testing depends on an exact blood-to-additive ratio, light blue tubes must be filled completely according to manufacturer guidelines.

 

Red Tube

Additive

Depending on the manufacturer:

• No additive
• Clot activator

Common Tests

Red-top tubes are commonly used for:

• Chemistry testing
• Serology
• Therapeutic drug monitoring
• Specialized laboratory testing

Clinical Tip

Blood collected in a red-top tube is generally allowed to clot before centrifugation.

 

Gold or Tiger-Top Tube (SST)

Additive

• Clot activator
• Serum separator gel

Common Tests

These tubes are commonly used for:

• Comprehensive Metabolic Panel (CMP)
• Basic Metabolic Panel (BMP)
• Lipid panel
• Liver function tests
• Thyroid testing
• Many routine chemistry tests

Clinical Tip

After centrifugation, the separator gel forms a barrier between the serum and blood cells, helping preserve specimen quality.

 

Green Tube

Additive

Heparin (lithium, sodium, or ammonium)

Common Tests

Green-top tubes are commonly used for:

• Plasma chemistry testing
• Electrolyte testing
• Certain STAT laboratory tests

Clinical Tip

Heparin prevents clot formation, allowing plasma to be analyzed quickly.

 

Lavender Tube

Additive

EDTA

Common Tests

Lavender tubes are commonly used in hematology for:

• Complete Blood Count (CBC)
• Hemoglobin
• Hematocrit
• White blood cell differential
• Hemoglobin A1C

Clinical Tip

EDTA preserves blood cell morphology, making it the preferred additive for hematology testing.

 

Pink Tube

Additive

EDTA

Common Tests

Pink-top tubes are used primarily by the blood bank for:

• Type and Screen
• Crossmatch
• Compatibility testing

Clinical Tip

Although both lavender and pink tubes contain EDTA, they are intended for different laboratory departments and should not be used interchangeably.

 

Gray Tube

Additive

Typically contains:

• Sodium fluoride
• Potassium oxalate

Common Tests

Gray-top tubes are commonly used for:

• Glucose testing
• Glucose tolerance testing
• Lactate levels
• Blood alcohol testing

Clinical Tip

The additives slow cellular metabolism, helping preserve accurate glucose levels after collection.

 

Yellow Tube

Additive

Depending on the manufacturer:

• Sodium Polyanethol Sulfonate (SPS)
• Acid Citrate Dextrose (ACD)

Common Tests

Yellow-top tubes may be used for:

• Blood cultures
• HLA testing
• Genetic studies
• Specialized immunohematology testing

Clinical Tip

Blood culture collection requires strict aseptic technique to minimize contamination.

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Common Tube Colors and Tests Chart

Tube Color	Additive	Common Tests
Light Blue	Sodium Citrate	PT, INR, aPTT
Red	None or Clot Activator	Chemistry, Serology
Gold/Tiger Top	Clot Activator + Gel	CMP, BMP, Lipid Panel
Green	Heparin	Plasma Chemistry
Lavender	EDTA	CBC, Hematology
Pink	EDTA	Blood Bank Testing
Gray	Sodium Fluoride/Potassium Oxalate	Glucose, Lactate
Yellow	SPS or ACD	Blood Cultures, Specialized Testing

Why Correct Tube Selection Matters

Choosing the wrong collection tube may result in:

• Specimen rejection
• Delayed laboratory results
• Repeat blood collections
• Additive contamination
• Inaccurate test results
• Delays in diagnosis and treatment

Even a perfectly collected specimen may be unusable if the incorrect tube is selected.

 

Tube Color vs. Tube Additive

A common misconception is that the tube color itself determines which tests can be performed.

In reality, the additive inside the tube is what matters most.

Although manufacturers may use slightly different shades or labeling, the additive determines the specimen requirements and testing applications.

Successful medical assistants learn both the tube colors and the additives associated with each tube.

 

Order of Draw Matters

Understanding tube colors goes hand in hand with understanding the order of draw.

Following the proper sequence helps prevent additive carryover between tubes and protects specimen integrity.

The standard order of draw is:

1. Blood Cultures
2. Light Blue
3. Serum Tubes (Red, Gold, Tiger Top)
4. Green
5. Lavender/Pink
6. Gray

Following the correct order helps improve specimen quality and supports accurate laboratory testing.

 

Why Medical Assistants Need to Know Tube Colors

Many medical assistants perform venipuncture daily in physician offices, urgent care centers, specialty practices, and outpatient clinics.

Knowing which tube to use helps medical assistants:

• Collect quality laboratory specimens
• Prevent collection errors
• Reduce repeat venipunctures
• Improve workflow efficiency
• Support timely diagnosis and treatment
• Provide safer patient care

Knowledge of tube selection is also commonly evaluated during certification exams, competency assessments, and employer training programs.

 

Continue Building Your Clinical Knowledge

Blood collection procedures and laboratory requirements continue to evolve. Ongoing education helps medical assistants stay current with best practices and improve patient care.

Continuing education topics include:

• Specimen integrity
• Order of draw
• Venipuncture techniques
• Laboratory quality assurance
• Infection prevention
• OSHA and CLIA requirements
• Patient safety

Continuing education through MARenew helps medical assistants strengthen their clinical skills, maintain certification requirements, and remain confident in today's healthcare environment.

Final Thoughts

Understanding blood collection tube colors is an essential clinical skill for medical assistants who perform venipuncture. Knowing the purpose of each tube, its additive, and the laboratory tests it supports helps ensure specimen quality, accurate results, and positive patient outcomes.

By mastering tube selection, following the correct order of draw, and continuing to build clinical knowledge, medical assistants play a vital role in delivering safe, efficient, and high-quality patient care.

References

1. Centers for Disease Control and Prevention. (n.d.). Laboratory quality resources. https://www.cdc.gov/labquality/
2. Clinical and Laboratory Standards Institute. (2017). Collection of diagnostic venous blood specimens (GP41). Clinical and Laboratory Standards Institute. https://clsi.org/standards/products/general-laboratory/documents/gp41/
3. World Health Organization. (2010). WHO guidelines on drawing blood: Best practices in phlebotomy. World Health Organization. https://www.ncbi.nlm.nih.gov/books/NBK138650/
4. American Association of Medical Assistants. (n.d.). Clinical practice resources. https://www.aama-ntl.org
5. U.S. Bureau of Labor Statistics. (2025). Medical assistants. Occupational Outlook Handbook. https://www.bls.gov/ooh/healthcare/medical-assistants.htm