CPT Phlebotomy Order of Draw Practice Exam Study Guide Updated 2026
| Verified Questions and Answers with Detailed Rationales | Order
of Draw Sequence (Blood Culture, Light Blue, Red, Gold/SST, Green,
Lavender, Gray), Tube Additives and Color Codes, Specimen Collection
Techniques, Venipuncture Procedures, Contamination Prevention, CLSI
Guidelines, Specimen Handling and Processing, Patient Safety and
Identification, Laboratory Accuracy and Quality Control, CPT Certification
Exam Prep | Complete Exam Prep Resource for Phlebotomy Technician
Success
Question 1: What is the correct first tube in the CLSI standard order of draw for
venipuncture?
A. Light blue top sodium citrate tube
B. Red top plain serum tube
C. Yellow top blood culture bottle
D. Lavender top EDTA tube
CORRECT ANSWER: C. Yellow top blood culture bottle
RATIONALE: Blood culture bottles must always be collected first in the order of draw to
minimize the risk of microbial contamination from the venipuncture site. Collecting
blood cultures first ensures that any skin flora introduced during needle insertion does
not contaminate the specimen, which could lead to false-positive culture results and
inappropriate antibiotic therapy
open-exam-prep.com
.
Question 2: Which tube additive requires a precise 9:1 blood-to-additive ratio for
accurate test results?
A. EDTA in lavender top tubes
B. Sodium citrate in light blue top tubes
C. Heparin in green top tubes
D. Sodium fluoride in gray top tubes
CORRECT ANSWER: B. Sodium citrate in light blue top tubes
RATIONALE: Light blue top tubes containing sodium citrate require an exact 9:1 ratio of
blood to anticoagulant for accurate coagulation testing (PT, PTT, INR). Underfilled citrate
tubes contain excess anticoagulant relative to blood volume, which falsely prolongs
clotting times and may lead to specimen rejection
open-exam-prep.com
.
,Question 3: What is the primary purpose of inverting blood collection tubes after
venipuncture?
A. To cool the specimen to room temperature
B. To ensure proper mixing of blood with tube additives
C. To activate the clotting process in serum tubes
D. To remove air bubbles from the collection system
CORRECT ANSWER: B. To ensure proper mixing of blood with tube additives
RATIONALE: Gentle inversion immediately after collection ensures thorough mixing of
blood with the tube's additive, preventing microclot formation in anticoagulant tubes
and ensuring accurate test results. Vigorous shaking should be avoided as it causes
hemolysis, which can interfere with multiple analytes
open-exam-prep.com
.
Question 4: If a lavender top EDTA tube is accidentally drawn before a light blue
citrate tube, which laboratory result is most likely to be affected?
A. Falsely decreased potassium levels
B. Falsely prolonged PT and PTT values
C. Falsely elevated glucose concentration
D. Falsely decreased white blood cell count
CORRECT ANSWER: B. Falsely prolonged PT and PTT values
RATIONALE: EDTA is a potent calcium chelator. If EDTA carryover occurs into a citrate
tube, it binds additional calcium beyond what the citrate is designed to bind, disrupting
the calcium-dependent coagulation cascade and producing falsely prolonged
prothrombin time (PT) and partial thromboplastin time (PTT) results
open-exam-prep.com
.
Question 5: How many gentle inversions are recommended for a green top heparin
tube after collection?
A. 2-3 inversions
B. 3-4 inversions
C. 5 inversions
D. 8-10 inversions
CORRECT ANSWER: D. 8-10 inversions
RATIONALE: Green top tubes containing heparin require 8-10 gentle inversions
immediately after collection to ensure adequate mixing of blood with the anticoagulant.
,Insufficient mixing may result in microclot formation, while excessive or vigorous mixing
can cause hemolysis
open-exam-prep.com
.
Question 6: Which tube should be collected immediately after blood culture
bottles in the standard order of draw?
A. Red top plain serum tube
B. Light blue top sodium citrate tube
C. Gold top SST tube
D. Green top heparin tube
CORRECT ANSWER: B. Light blue top sodium citrate tube
RATIONALE: Following CLSI guidelines, the light blue top sodium citrate tube is
collected second in the order of draw, immediately after blood cultures. This positioning
protects coagulation specimens from contamination by additives in subsequent tubes
that could interfere with clotting factor analysis
open-exam-prep.com
.
Question 7: What is the maximum recommended time a tourniquet should remain
applied during venipuncture?
A. 30 seconds
B. 1 minute
C. 2 minutes
D. 3 minutes
CORRECT ANSWER: B. 1 minute
RATIONALE: Tourniquets should not remain applied for longer than 1 minute to prevent
hemoconcentration, which can falsely elevate levels of proteins, potassium, and
cellular elements. Prolonged tourniquet application may also cause patient discomfort
and compromise specimen integrity
open-exam-prep.com
.
Question 8: When using a butterfly needle collection set and the first tube ordered
is a light blue citrate tube, what additional step is required?
A. Warm the collection site for 3 minutes
B. Draw a discard tube before collecting the citrate tube
C. Use a smaller gauge needle to reduce hemolysis
D. Collect the citrate tube using a syringe instead
, CORRECT ANSWER: B. Draw a discard tube before collecting the citrate tube
RATIONALE: Butterfly needle sets contain approximately 0.5 mL of dead space in the
tubing. When a citrate tube is the first tube collected with a butterfly set, this dead
space causes the tube to be underfilled, altering the critical 9:1 blood-to-citrate ratio. A
discard tube (typically plain red) should be drawn first to fill the dead space
open-exam-prep.com
.
Question 9: Which additive is contained in gray top blood collection tubes?
A. Sodium citrate
B. Lithium heparin
C. EDTA
D. Sodium fluoride and potassium oxalate
CORRECT ANSWER: D. Sodium fluoride and potassium oxalate
RATIONALE: Gray top tubes contain sodium fluoride (a glycolytic inhibitor that prevents
glucose metabolism by blood cells) and potassium oxalate (an anticoagulant). These
additives preserve glucose levels for accurate testing and are why gray tubes are drawn
last in the order of draw to prevent contamination of other specimens
open-exam-prep.com
.
Question 10: What is the primary reason gray top tubes are positioned last in the
order of draw?
A. They contain the most contaminating additives
B. They require the longest centrifugation time
C. They are used for the least critical laboratory tests
D. They have the smallest blood volume capacity
CORRECT ANSWER: A. They contain the most contaminating additives
RATIONALE: Gray top tubes contain potassium oxalate and sodium fluoride, which are
highly contaminating additives. Drawing these tubes last minimizes the risk of additive
carryover into other specimens, which could significantly alter test results for
chemistry, hematology, and coagulation assays
open-exam-prep.com
.
Question 11: Which tube is appropriate for collecting a specimen for a complete
blood count (CBC)?
| Verified Questions and Answers with Detailed Rationales | Order
of Draw Sequence (Blood Culture, Light Blue, Red, Gold/SST, Green,
Lavender, Gray), Tube Additives and Color Codes, Specimen Collection
Techniques, Venipuncture Procedures, Contamination Prevention, CLSI
Guidelines, Specimen Handling and Processing, Patient Safety and
Identification, Laboratory Accuracy and Quality Control, CPT Certification
Exam Prep | Complete Exam Prep Resource for Phlebotomy Technician
Success
Question 1: What is the correct first tube in the CLSI standard order of draw for
venipuncture?
A. Light blue top sodium citrate tube
B. Red top plain serum tube
C. Yellow top blood culture bottle
D. Lavender top EDTA tube
CORRECT ANSWER: C. Yellow top blood culture bottle
RATIONALE: Blood culture bottles must always be collected first in the order of draw to
minimize the risk of microbial contamination from the venipuncture site. Collecting
blood cultures first ensures that any skin flora introduced during needle insertion does
not contaminate the specimen, which could lead to false-positive culture results and
inappropriate antibiotic therapy
open-exam-prep.com
.
Question 2: Which tube additive requires a precise 9:1 blood-to-additive ratio for
accurate test results?
A. EDTA in lavender top tubes
B. Sodium citrate in light blue top tubes
C. Heparin in green top tubes
D. Sodium fluoride in gray top tubes
CORRECT ANSWER: B. Sodium citrate in light blue top tubes
RATIONALE: Light blue top tubes containing sodium citrate require an exact 9:1 ratio of
blood to anticoagulant for accurate coagulation testing (PT, PTT, INR). Underfilled citrate
tubes contain excess anticoagulant relative to blood volume, which falsely prolongs
clotting times and may lead to specimen rejection
open-exam-prep.com
.
,Question 3: What is the primary purpose of inverting blood collection tubes after
venipuncture?
A. To cool the specimen to room temperature
B. To ensure proper mixing of blood with tube additives
C. To activate the clotting process in serum tubes
D. To remove air bubbles from the collection system
CORRECT ANSWER: B. To ensure proper mixing of blood with tube additives
RATIONALE: Gentle inversion immediately after collection ensures thorough mixing of
blood with the tube's additive, preventing microclot formation in anticoagulant tubes
and ensuring accurate test results. Vigorous shaking should be avoided as it causes
hemolysis, which can interfere with multiple analytes
open-exam-prep.com
.
Question 4: If a lavender top EDTA tube is accidentally drawn before a light blue
citrate tube, which laboratory result is most likely to be affected?
A. Falsely decreased potassium levels
B. Falsely prolonged PT and PTT values
C. Falsely elevated glucose concentration
D. Falsely decreased white blood cell count
CORRECT ANSWER: B. Falsely prolonged PT and PTT values
RATIONALE: EDTA is a potent calcium chelator. If EDTA carryover occurs into a citrate
tube, it binds additional calcium beyond what the citrate is designed to bind, disrupting
the calcium-dependent coagulation cascade and producing falsely prolonged
prothrombin time (PT) and partial thromboplastin time (PTT) results
open-exam-prep.com
.
Question 5: How many gentle inversions are recommended for a green top heparin
tube after collection?
A. 2-3 inversions
B. 3-4 inversions
C. 5 inversions
D. 8-10 inversions
CORRECT ANSWER: D. 8-10 inversions
RATIONALE: Green top tubes containing heparin require 8-10 gentle inversions
immediately after collection to ensure adequate mixing of blood with the anticoagulant.
,Insufficient mixing may result in microclot formation, while excessive or vigorous mixing
can cause hemolysis
open-exam-prep.com
.
Question 6: Which tube should be collected immediately after blood culture
bottles in the standard order of draw?
A. Red top plain serum tube
B. Light blue top sodium citrate tube
C. Gold top SST tube
D. Green top heparin tube
CORRECT ANSWER: B. Light blue top sodium citrate tube
RATIONALE: Following CLSI guidelines, the light blue top sodium citrate tube is
collected second in the order of draw, immediately after blood cultures. This positioning
protects coagulation specimens from contamination by additives in subsequent tubes
that could interfere with clotting factor analysis
open-exam-prep.com
.
Question 7: What is the maximum recommended time a tourniquet should remain
applied during venipuncture?
A. 30 seconds
B. 1 minute
C. 2 minutes
D. 3 minutes
CORRECT ANSWER: B. 1 minute
RATIONALE: Tourniquets should not remain applied for longer than 1 minute to prevent
hemoconcentration, which can falsely elevate levels of proteins, potassium, and
cellular elements. Prolonged tourniquet application may also cause patient discomfort
and compromise specimen integrity
open-exam-prep.com
.
Question 8: When using a butterfly needle collection set and the first tube ordered
is a light blue citrate tube, what additional step is required?
A. Warm the collection site for 3 minutes
B. Draw a discard tube before collecting the citrate tube
C. Use a smaller gauge needle to reduce hemolysis
D. Collect the citrate tube using a syringe instead
, CORRECT ANSWER: B. Draw a discard tube before collecting the citrate tube
RATIONALE: Butterfly needle sets contain approximately 0.5 mL of dead space in the
tubing. When a citrate tube is the first tube collected with a butterfly set, this dead
space causes the tube to be underfilled, altering the critical 9:1 blood-to-citrate ratio. A
discard tube (typically plain red) should be drawn first to fill the dead space
open-exam-prep.com
.
Question 9: Which additive is contained in gray top blood collection tubes?
A. Sodium citrate
B. Lithium heparin
C. EDTA
D. Sodium fluoride and potassium oxalate
CORRECT ANSWER: D. Sodium fluoride and potassium oxalate
RATIONALE: Gray top tubes contain sodium fluoride (a glycolytic inhibitor that prevents
glucose metabolism by blood cells) and potassium oxalate (an anticoagulant). These
additives preserve glucose levels for accurate testing and are why gray tubes are drawn
last in the order of draw to prevent contamination of other specimens
open-exam-prep.com
.
Question 10: What is the primary reason gray top tubes are positioned last in the
order of draw?
A. They contain the most contaminating additives
B. They require the longest centrifugation time
C. They are used for the least critical laboratory tests
D. They have the smallest blood volume capacity
CORRECT ANSWER: A. They contain the most contaminating additives
RATIONALE: Gray top tubes contain potassium oxalate and sodium fluoride, which are
highly contaminating additives. Drawing these tubes last minimizes the risk of additive
carryover into other specimens, which could significantly alter test results for
chemistry, hematology, and coagulation assays
open-exam-prep.com
.
Question 11: Which tube is appropriate for collecting a specimen for a complete
blood count (CBC)?
