Order of Draw and Tube Selection Practice Questions for NHA CPT

Mastering the order of draw and proper tube selection is absolutely critical for success on the NHA Certified Phlebotomy Technician (CPT) examination and for safe, effective clinical practice. This topic comprises a significant portion of the Routine Blood Collections domain, which accounts for 28-30% of the entire exam, making it one of the most heavily weighted areas you’ll encounter. Understanding the correct sequence of tube collection prevents cross-contamination of additives between specimens, which can lead to inaccurate test results, misdiagnosis, and potentially harmful patient outcomes. Each colored tube top corresponds to specific additives and anticoagulants designed for particular laboratory tests, and knowing which tube to use for each test type is essential knowledge for any competent phlebotomy technician. The order of draw follows a specific sequence: blood culture bottles first, followed by light blue (coagulation), then red or gold (serum), green (heparin), lavender (EDTA), and finally gray (glucose) tubes. Beyond simply memorizing this sequence, successful candidates must understand the rationale behind each step, including why coagulation tubes must be drawn before other additive tubes and why glucose tubes come last. Additionally, proper tube handling techniques, such as the correct number of inversions for each tube type and maintaining the proper blood-to-additive ratio (especially critical for coagulation studies), are frequently tested concepts. Many candidates report that questions about tube colors, additives, and the order of draw appear throughout the exam, often integrated into scenario-based questions that test your ability to apply this knowledge in realistic clinical situations. Capillary collection procedures follow a different order than venipuncture, with EDTA tubes collected first to minimize platelet clumping, representing another layer of complexity that the exam assesses. The consequences of errors in tube selection or order of draw can be severe, ranging from specimen rejection and patient recollection to delayed diagnosis and treatment, which is why regulatory bodies like CLSI (Clinical and Laboratory Standards Institute) have established strict guidelines that all phlebotomy technicians must follow. By thoroughly understanding these principles and practicing with realistic questions, you’ll build the confidence and competence needed to excel on this crucial section of the NHA CPT exam.

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Practice Questions

Question 1

What is the correct order of draw for venipuncture using evacuated tubes?

A) Light blue, red, green, lavender, gray
B) Yellow (blood culture), light blue, red, green, lavender, gray
C) Red, light blue, green, lavender, gray
D) Lavender, green, red, light blue, yellow

Correct Answer: B

Explanation: The proper order of draw is: blood culture bottles (yellow), light blue (coagulation), red or gold (serum), green (heparin), lavender (EDTA), and gray (glucose). This order prevents cross-contamination of additives between tubes and ensures accurate test results.

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Question 2

Which tube should be drawn first when collecting specimens for coagulation studies?

A) Red top tube
B) Light blue top tube
C) Lavender top tube
D) Green top tube

Correct Answer: B

Explanation: The light blue top tube (sodium citrate) for coagulation studies should be drawn first among additive tubes, or second if blood cultures are needed. This prevents contamination from other anticoagulants that could affect coagulation test results.

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Question 3

A lavender top tube contains which anticoagulant?

A) Sodium citrate
B) Heparin
C) EDTA (Ethylenediaminetetraacetic acid)
D) Sodium fluoride

Correct Answer: C

Explanation: Lavender (purple) top tubes contain EDTA, which prevents blood clotting by binding calcium. These tubes are primarily used for hematology tests such as complete blood counts (CBC).

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Question 4

How many times should a tube containing an anticoagulant be inverted immediately after collection?

A) 2-3 times
B) 5-10 times
C) 15-20 times
D) No inversion is necessary

Correct Answer: B

Explanation: Tubes with anticoagulants should be gently inverted 5-10 times immediately after collection to ensure proper mixing of blood with the additive. This prevents clotting and ensures accurate test results. Vigorous shaking should be avoided as it can cause hemolysis.

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Question 5

Which tube is used for glucose testing and contains sodium fluoride?

A) Red top tube
B) Gray top tube
C) Green top tube
D) Light blue top tube

Correct Answer: B

Explanation: Gray top tubes contain sodium fluoride (antiglycolytic agent) and potassium oxalate (anticoagulant). The sodium fluoride preserves glucose by preventing glycolysis, making these tubes ideal for glucose and lactate testing.

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Question 6

What is the primary reason for following the correct order of draw?

A) To save time during collection
B) To prevent cross-contamination of additives between tubes
C) To make labeling easier
D) To reduce patient discomfort

Correct Answer: B

Explanation: The order of draw is critical to prevent cross-contamination of tube additives, which can lead to inaccurate test results. Additives from one tube can be transferred to subsequent tubes via the needle, potentially affecting test outcomes.

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Question 7

A green top tube contains which anticoagulant?

A) EDTA
B) Sodium citrate
C) Heparin
D) No anticoagulant

Correct Answer: C

Explanation: Green top tubes contain heparin (either sodium or lithium heparin), which prevents clotting by inhibiting thrombin formation. These tubes are commonly used for chemistry tests requiring plasma.

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Question 8

Which tube should be used for blood bank testing and crossmatching?

A) Lavender top tube
B) Pink top tube or red top tube
C) Green top tube
D) Gray top tube

Correct Answer: B

Explanation: Pink top tubes (EDTA) or red top tubes (no additive) are specifically used for blood bank testing, type and crossmatch procedures. Pink tubes are preferred in many facilities as they are designated specifically for blood bank use to prevent mix-ups.

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Question 9

When performing a dermal puncture (capillary collection), what is the correct order of collection?

A) Lavender, then other tubes
B) EDTA tubes last
C) Lavender microtainer first, then other tubes
D) No specific order is required

Correct Answer: C

Explanation: For capillary collections, the order differs from venipuncture. EDTA tubes (lavender) should be collected first to minimize platelet clumping, followed by other additive tubes, and then serum tubes last.

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Question 10

A red top tube with no additive is used for which type of testing?

A) Hematology
B) Coagulation
C) Serum chemistry and serology
D) Glucose testing

Correct Answer: C

Explanation: Red top tubes contain no additives and allow blood to clot naturally. After centrifugation, serum is obtained and used for chemistry tests, serology, and immunology studies.

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Question 11

What is the purpose of the sodium citrate in a light blue top tube?

A) To preserve glucose levels
B) To bind calcium and prevent coagulation
C) To separate serum from cells
D) To prevent hemolysis

Correct Answer: B

Explanation: Sodium citrate in light blue tubes binds calcium ions, which are essential for the coagulation cascade. This prevents clotting and preserves the specimen for coagulation studies such as PT, PTT, and INR.

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Question 12

Which tube should be drawn last in the order of draw?

A) Light blue top tube
B) Red top tube
C) Gray top tube
D) Green top tube

Correct Answer: C

Explanation: Gray top tubes (containing sodium fluoride and potassium oxalate) should be drawn last in the order of draw. This prevents contamination of other tubes with the antiglycolytic agent, which could interfere with other test results.

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Question 13

What is the blood-to-additive ratio for a light blue top coagulation tube?

A) 5:1
B) 9:1
C) 10:1
D) No specific ratio required

Correct Answer: B

Explanation: Light blue top tubes require a precise 9:1 blood-to-additive ratio (9 parts blood to 1 part sodium citrate). Underfilling or overfilling these tubes can lead to inaccurate coagulation test results.

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Question 14

A gold or red-gray “tiger top” tube contains what type of additive?

A) Anticoagulant only
B) Clot activator and gel separator
C) EDTA
D) Sodium fluoride

Correct Answer: B

Explanation: Gold or SST (serum separator tube) tubes contain a clot activator to speed clotting and a gel separator that forms a barrier between serum and cells after centrifugation. These are commonly used for chemistry tests.

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Question 15

When collecting blood cultures, which tube or bottle should be drawn first?

A) Aerobic bottle
B) Anaerobic bottle
C) Either bottle, order doesn’t matter
D) Light blue top tube

Correct Answer: B

Explanation: When collecting blood cultures, the anaerobic bottle should be drawn first, followed by the aerobic bottle. This is because some air may enter the anaerobic bottle during collection, and drawing it first minimizes oxygen exposure. However, some facilities may follow different protocols, so always follow institutional guidelines.

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Study Tips

• Create flashcards with tube colors on one side and their additives/uses on the other
• Practice writing out the order of draw from memory multiple times daily
• Use mnemonics to remember the sequence (e.g., “Yellow Light Brings Good Luck Generally”)
• Pay special attention to the 9:1 ratio requirement for light blue tubes
• Remember that capillary collection order differs from venipuncture
• Review CLSI guidelines for the most current standards

Good luck with your NHA CPT exam preparation!