🚧 Under construction — VoTechWorks is being built. A free tech program — complimentary, as our commitment to get America working.
voTechWorksGrade 13 · a vocational technology learning center, by urbanicity
newSchoolWorks.com › VoTechWorks › Health & Personal Services › Medical Assisting › Phlebotomy: Venipuncture, Capillary Collection, and Specimen Handling › Lesson 3
HLT-MEDI38-03 · Lesson 3 · 10.5 clock hours · demo

Equipment Identification: Tubes, Additives, Order of Draw, and Supplies

Objective. Students correctly identify all common evacuated tube types by color, state each tube's additive and mechanism of action, and recite the current CLSI-recommended order of draw for a multi-tube draw.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Tube Identification Matters

Every evacuated collection tube is engineered to do a specific job. Placing blood in the wrong tube—or drawing tubes in the wrong order—can cause erroneous laboratory results, patient harm, and repeated venipunctures. As a medical assistant, you must recognize each tube instantly and know exactly where it belongs in a multi-tube draw.

Evacuated Tube System Overview

The evacuated tube system (ETS) uses a vacuum-sealed tube, a double-pointed needle, and a tube holder (adapter) to draw blood directly from the vein. The needle's rear end punctures the rubber stopper and the vacuum pulls blood into the tube. Tubes contain measured amounts of additives—chemicals that either preserve the specimen or allow it to clot in a controlled way.

Safety note: Never remove the stopper of a filled tube to transfer blood between tubes. This changes the blood-to-additive ratio and creates a splash exposure risk.

Common Tube Colors, Additives, and Uses

Yellow — Blood Culture / SPS

Contains sodium polyanethol sulfonate (SPS), an anticoagulant that inhibits complement and phagocytosis so bacteria survive transport. Used for blood cultures. Always collected first to avoid microbial contamination from skin flora.

Light Blue — Sodium Citrate

Sodium citrate binds (chelates) calcium ions, reversibly preventing coagulation. The ratio of blood to additive is critical (typically 9:1). Used for coagulation studies: PT/INR, aPTT. If a butterfly needle is used, a discard tube is drawn first to purge air so the light-blue tube fills completely.

Red — No Additive (Plain)

Contains no additive; blood clots naturally. Used for serum chemistry tests and serology. Allow the tube to clot before centrifugation.

Gold / SST (Serum Separator Tube) — Clot Activator + Gel

Contains silica particles (clot activator) and an inert polymer gel. After centrifugation, the gel forms a barrier between serum and cells. Used for most routine chemistry panels: BMP, CMP, thyroid tests, drug levels. Invert 5 times after collection.

Green — Lithium Heparin or Sodium Heparin

Heparin inhibits thrombin and thromboplastin, preventing clot formation and yielding plasma. Used for stat chemistry tests and some special studies. Invert 8–10 times. Lithium heparin is most common; do not use for lithium level testing.

Lavender (Purple) — EDTA (Ethylenediaminetetraacetic Acid)

EDTA chelates calcium ions irreversibly, preventing coagulation and preserving cell morphology. Used for hematology: CBC, differential, blood smear, HbA1c, blood typing. Invert 8–10 times immediately after collection.

Gray — Potassium Oxalate / Sodium Fluoride

Sodium fluoride inhibits glycolysis (the breakdown of glucose by red blood cells), preserving glucose concentration. Potassium oxalate acts as an anticoagulant. Used for glucose and alcohol levels. Invert 8–10 times.

CLSI-Recommended Order of Draw

The Clinical and Laboratory Standards Institute (CLSI) document GP41 establishes the order of draw to minimize additive carryover between tubes. Carryover occurs when trace amounts of one tube's additive contaminate the next tube via the needle.

Current CLSI order for ETS (multi-tube draw):

1. Blood cultures (yellow / sterile bottles)

2. Sodium citrate (light blue)

3. Serum tubes — red (no additive), then gold/SST

4. Heparin tubes (green)

5. EDTA tubes (lavender)

6. Glycolytic inhibitor tubes (gray)

A common memory aid: "Boy Scout Always Goes Lightly Gray" (Blood culture → Sodium citrate → Serum → Green/heparin → Lavender/EDTA → Gray).

Why does order matter? EDTA is a powerful anticoagulant; if it carries over into a coagulation tube (light blue), it falsely prolongs clotting times. Sodium citrate carryover into a chemistry tube alters calcium results.

Mixing and Handling

After filling each tube, gently invert it the number of times specified by the manufacturer (usually 5–10) to mix blood with additive. Do not shake; shaking causes hemolysis. Hemolyzed specimens interfere with many chemistry assays and may require recollection.

Label every tube at the patient's side, immediately after collection, before leaving the room. Include patient name, date of birth, date, time, and collector's ID.

Needle and Supply Selection

Safety Priorities

Key terms10

Evacuated tube system (ETS)A blood collection system consisting of a vacuum-sealed tube, a double-pointed needle, and a tube holder; the vacuum draws a precise volume of blood into the tube.
AdditiveA chemical substance inside a collection tube that acts on blood to preserve, anticoagulate, or separate components for a specific type of laboratory test.
Order of drawThe CLSI-recommended sequence in which evacuated tubes are filled during a multi-tube venipuncture to prevent additive carryover between tubes.
Additive carryoverThe inadvertent transfer of a trace amount of one tube's additive into the next tube via the needle, which can falsify laboratory results.
HemolysisThe rupture of red blood cells, releasing hemoglobin and intracellular contents into the plasma or serum; it can interfere with many laboratory tests and is often caused by shaking tubes or improper technique.
EDTA (Ethylenediaminetetraacetic acid)An anticoagulant additive in lavender-top tubes that irreversibly chelates calcium ions, preventing clotting and preserving cell morphology for hematology testing.
Sodium citrateA reversible calcium-chelating anticoagulant in light-blue tubes used for coagulation studies; the blood-to-additive ratio must be maintained for accurate results.
Serum separator tube (SST)A gold-top tube containing a clot activator and polymer gel that, after centrifugation, forms a physical barrier between serum and cells for chemistry testing.
Sodium fluorideAn additive in gray-top tubes that inhibits glycolysis, preserving glucose levels in a blood specimen until it can be tested.
CLSI GP41The Clinical and Laboratory Standards Institute document that provides standardized guidelines for venipuncture technique, including the recommended order of draw.
In class: Handle a tray of actual evacuated tubes (yellow, light blue, red, gold/SST, green, lavender, gray) and complete an equipment identification card for each tube: color, additive, mode of action, and one common laboratory test ordered into that tube. · Watch the instructor perform a timed order-of-draw demonstration using a venipuncture training arm; students call out the next tube in sequence and correct any deviations before the instructor advances. · Complete a matching worksheet that presents 15 physician orders (e.g., CBC, PT/INR, BMP, blood culture) and requires students to select correct tube type(s) and arrange them in proper draw order.
Materials: Full set of evacuated collection tubes (real or simulation), tube holder/adapters, butterfly needle sets, straight multi-sample needles (21g and 23g), tourniquets, alcohol prep pads, gauze, bandages, CLSI GP41 order-of-draw reference card
Check: Students score 80% or higher on a practical tube-identification quiz in which the instructor holds up random tubes and asks students to state additive, use, and position in the order of draw.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Phlebotomy / Specimen Collection
1. A physician orders a CBC and a BMP on the same patient. In what order should the tubes be drawn?
Phlebotomy / Specimen Collection
2. A medical assistant draws a light-blue sodium citrate tube for a PT/INR using a butterfly needle. What additional step is required that is not needed with a straight needle?
Clinical Laboratory / Specimen Handling
3. Which additive in gray-top tubes prevents falsely low glucose results by stopping cellular metabolism of glucose?
Phlebotomy / Order of Draw
4. A lavender-top tube is drawn before a light-blue tube by mistake. Which result is most likely to be affected?
Phlebotomy / Order of Draw
5. Which collection tube should be drawn FIRST in a multi-tube venipuncture that includes a blood culture?
Specimen Handling / Quality Control
6. A medical assistant shakes a lavender-top tube vigorously to mix the EDTA. What is the most likely consequence?
Specimen Handling / Patient Safety
7. A physician orders a PT/INR and a CBC. The medical assistant has already filled the light-blue tube but notices the tube is only three-quarters full. What is the correct action?
Clinical Sciences / Laboratory Testing
8. Which statement correctly describes the mechanism of action of lithium heparin in a green-top tube?
Record this lesson on my transcript. Sign in with your key and enrollment email to record lessons (enroll free if you have no key). This page stays open to read and practise.
← Previous lessonProgram planNext lesson →