LET’S GET THIS OUT OF THE WAY: NEVER POUR ONE TUBE INTO ANOTHER. Doing this can cause all kinds of problems with testing.
Moving on…
When a phlebotomist draws tubes for the lab, they are color codes to easily distinguish which is used for what purpose. So, for example, if the orders are for a BMP and a CBC, the phlebotomist knows they can draw a green top and a lavender top. And if they are drawing a PT, they know they need to get a light blue top tube. These are standardized and knowledge can generally be used across different hospitals and clinics.
So, we’ll start with the most common types and then move to the less common tubes that are used for specialty testing not done in most laboratories.
Common Types of Tubes, by Color
Light Blue Top Tube
Additive: Sodium Citrate (anticoagulant)
Used for: Coagulation studies (PT, APTT, D-dimer, fibrinogen)
Concerns/Limitations: Must be filled to the correct volume to ensure proper anticoagulation; otherwise, results may be inaccurate.
Some coagulation test require special blue top tubes made of glass instead of plastic.
Red Top Tube
Additive: None (sometimes a clot activator)
Used for: Serum testing (chemistry, serology, blood bank)
Concerns/Limitations: Requires time for blood clot formation before centrifugation (usually 30 minutes); not suitable for urgent or STAT testing unless processed quickly.
Gold Top Tube (SST - Serum Separator Tube) or Tiger Top Tube (Red and Black striped cap)
Additive: Clot activator and gel for serum separation
Used for: Serum testing (chemistry panels, immunology, serology)
Concerns/Limitations: The gel can interfere with certain drug levels and other sensitive assays, so the tube may not be suitable for some specific tests.
Green Top Tube
Additive: Heparin (either lithium or sodium heparin)
Used for: Plasma testing (chemistry tests, including electrolyte panels and ammonia levels)
Concerns/Limitations: Heparin can interfere with some assays, such as coagulation tests, and must be selected carefully depending on the test ordered.
Lavender (or Purple) Top Tube
Additive: EDTA (anticoagulant)
Used for: Hematology (CBC, blood smears, blood typing, HbA1c)
Concerns/Limitations: EDTA can interfere with certain chemistry tests and clotting factor assays, so it is unsuitable for tests other than hematology.
Pink Top Tube
Additive: EDTA (anticoagulant)
Used for: Blood bank testing (crossmatch, type, and screen)
Concerns/Limitations: Similar to the lavender tube but specifically designated for blood banking to avoid mix-ups.
Since these are essentially the same as lavender top tubes, they can be used interchangeably if necessary.
Gray Top Tube
Additive: Potassium oxalate and sodium fluoride (anticoagulant and glycolysis inhibitor)
Used for: Glucose testing, lactate measurements, and alcohol levels
Concerns/Limitations: Not ideal for electrolyte or enzyme testing due to interference from the additives; the fluoride preserves glucose levels but also inhibits many enzymes.
Less common types of tubes used
Yellow Top Tube (ACD - Acid Citrate Dextrose)
Additive: Acid citrate dextrose
Used for: HLA typing, DNA studies, and some specialized immunological studies
Concerns/Limitations: Limited use outside of genetic or immunological testing; the anticoagulant is unsuitable for routine chemistry or hematology testing.
Royal Blue Top Tube
Additive: Sodium EDTA, or no additive depending on the tube
Used for: Trace element testing (zinc, copper, lead, mercury) and toxicology
Concerns/Limitations: Meticulously clean tubes are needed to avoid contamination of trace elements; EDTA versions are not appropriate for all trace elements.
Black Top Tube
Additive: Sodium citrate (similar to light blue, but at a higher concentration)
Used for: Erythrocyte Sedimentation Rate (ESR)
Concerns/Limitations: This tube is specifically designed for ESR and is unsuitable for other types of testing.
Tan Top Tube
Additive: EDTA (anticoagulant)
Used for: Lead testing
Concerns/Limitations: Specially treated to avoid lead contamination; not suitable for other testing purposes.
Orange Top Tube (RST - Rapid Serum Tube)
Additive: Thrombin (clot activator)
Used for: STAT serum testing (chemistry, cardiac markers)
Concerns/Limitations: Designed for rapid clotting, so it is ideal for urgent testing but may not be suitable for certain sensitive assays where clotting activators could interfere.
White Top Tube
Additive: EDTA with gel for plasma separation
Used for: Molecular diagnostics (PCR, viral loads, etc.)
Concerns/Limitations: EDTA may interfere with some assays, so it should be used only for the specific molecular tests for which it is intended.
SPS (Yellow Top) Tube
Additive: Sodium Polyanethol Sulfonate (SPS)
Used for: Blood culture collection for microbiological testing
Concerns/Limitations:
Prevents clotting: The SPS additive helps prevent blood from clotting and inhibits the immune system's response, allowing microorganisms to grow if present. This makes it ideal for isolating bacteria and fungi from the blood in cases of suspected septicemia or bloodstream infections.
Inhibits some antibiotics: SPS can neutralize certain antibiotics and complement proteins, which can help detect bacteria even if the patient is on antibiotics.
Limitations: Not suitable for routine blood testing, chemistry, or hematology tests. Strict sterility must be maintained to avoid contamination. Overfilling or underfilling the tube can affect the recovery of organisms, so the correct blood-to-additive ratio is essential for reliable results.
DRAW ORDER
1. Blood Cultures (and/or SPS)
Reason: Blood cultures are drawn first to avoid contamination by additives from other tubes, which could interfere with microbiological results.
Be sure to properly clean and decontaminate the area being drawn to prevent contamination.
2. Light Blue Top (Sodium Citrate)
Reason: This tube is used for coagulation studies, and it's important to draw it before tubes with additives that may interfere with clotting, such as EDTA or heparin.
Be sure to fill to the line (no more, no less) to ensure the proper ratio of blood to additive.
3. Gold Top or Tiger Top (SST - Serum Separator Tube) or Red Top (no additive)
Reason: The clot activator in the gold tube could contaminate subsequent tubes, so it’s drawn early after the citrate tube to avoid affecting plasma results.
4. Green Top (Heparin)
Reason: Heparin is an anticoagulant and should be drawn after tubes that require clotting, such as the SST. Drawing it later helps to prevent cross-contamination that could affect clot-based testing.
5. Lavender Top (EDTA) or Pink Top Blood Bank Tube
Reason: EDTA is a strong anticoagulant and can interfere with many other tests, especially coagulation and enzyme activity, so it is drawn later in the order to avoid contamination.
IF EDTA gets into other tubes it can greatly affect testing, so avoid cross-contamination.
6. Gray Top (Sodium Fluoride/Potassium Oxalate)
Reason: This tube is usually drawn last because it contains an additive that inhibits glycolysis and can affect enzyme and electrolyte testing in earlier tubes.
It is generally done with the tourniquet removed. When oxygen is cut off, cells go into anerobic respiration and produce lactic acid (what we are generally testing for with the gray top tube).
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