CLC PRACTICE EXAM 2026 | Clinical Laboratory Concepts |
A-Graded Q&A | CLSI/OSHA/NHA Standards | Pass
Guaranteed - A+ Graded
Section 1: Phlebotomy Procedures & Venipuncture Techniques
(Q1-22)
Q1. A phlebotomist is preparing to collect a complete blood count (CBC),
comprehensive metabolic panel (CMP), and prothrombin time (PT) from a patient.
According to the 2026 CLSI order of draw guidelines, which tube should be drawn
first?
A. Red top (no additive)
B. Light blue top (sodium citrate)
C. Green top (heparin)
D. Lavender top (EDTA)
Rationale: The light blue top (sodium citrate) for coagulation studies must be drawn
first when blood cultures are not ordered, as it is the most sensitive to tissue
thromboplastin contamination. Drawing EDTA or heparin first could contaminate
subsequent coagulation tubes and cause falsely prolonged clotting times.
Correct Answer: B
Q2. A patient presents for a fasting lipid panel and fasting glucose. The phlebotomist
notices the patient is drinking black coffee. Which action is most appropriate?
A. Proceed with the draw; black coffee does not affect fasting status
B. Cancel both tests and reschedule for another day
C. Proceed with the lipid panel but cancel the glucose test
D. Document the coffee intake and notify the ordering provider before proceeding
,Rationale: Black coffee without additives does not significantly affect fasting glucose
or lipid results, but proper documentation ensures transparency. Rescheduling is
unnecessary for black coffee, though cream/sugar would invalidate fasting status.
Correct Answer: A
Q3. During a routine venipuncture using a straight needle and holder, the
phlebotomist feels a "pop" as the needle enters the vein but no blood flows into the
tube. The bevel is fully within the vein. What is the most likely cause?
A. The needle angle is too steep
B. The tube vacuum has been lost
C. The tourniquet was applied too tightly
D. The patient has collapsed veins
Rationale: When the bevel is fully within the vein but no blood flows, the most
common cause is loss of tube vacuum, which can occur with expired tubes or if the
tube was previously punctured. A steep angle or collapsed veins would typically
prevent entry sensation.
Correct Answer: B
Q4. A phlebotomist is using a butterfly needle with a 12-inch tubing extension to
collect a light blue top and then a lavender top. According to CLSI guidelines, what
must be done to ensure proper additive-to-blood ratios?
A. Draw a discard tube before the light blue top
B. Invert the light blue top 8-10 times immediately after collection
C. Use a syringe instead of vacuum tubes
D. Apply the tourniquet only during the first tube fill
Rationale: When using butterfly systems with tubing extensions, a non-additive
discard tube must be drawn first to clear the air from the tubing; otherwise, the light
blue top will be underfilled, resulting in an incorrect 9:1 blood-to-citrate ratio.
,Inversion is important but does not address the underfill issue.
Correct Answer: A
Q5. A phlebotomist is preparing to draw blood from an obese patient whose
antecubital veins are not palpable. The patient states previous successful draws were
from the dorsal hand veins. Which equipment modification is most appropriate?
A. Use a 23-gauge butterfly needle with a warming pack
B. Use a 21-gauge straight needle with a standard tourniquet
C. Use a 25-gauge butterfly needle without a tourniquet
D. Use an 18-gauge straight needle with a blood pressure cuff
Rationale: Dorsal hand veins in obese patients are typically small and fragile; a 23-
gauge butterfly needle minimizes trauma while a warming pack promotes
vasodilation. A 21-gauge needle is too large for hand veins, and a 25-gauge may
cause hemolysis in certain tests.
Correct Answer: A
Q6. A phlebotomist draws a blood culture set from a patient with suspected sepsis.
The first bottle shows growth within 8 hours, while the second bottle remains
negative. Which pre-analytical error most likely explains this discrepancy?
A. Inadequate skin antisepsis leading to contamination of the first bottle
B. Drawing the aerobic bottle before the anaerobic bottle
C. Using a 23-gauge needle instead of a 21-gauge needle
D. Filling both bottles to exactly 10 mL each
Rationale: Rapid growth in only one bottle of a blood culture set strongly suggests
skin flora contamination due to inadequate antisepsis. The correct order is aerobic
then anaerobic, but order reversal would not cause selective growth. Needle gauge
and exact fill volumes do not explain this pattern.
Correct Answer: A
, Q7. A patient requires a therapeutic drug monitoring (TDM) draw for phenytoin at
trough level. The patient received their last dose at 8:00 PM yesterday. When should
the blood be drawn?
A. 6:00 AM, before the next scheduled dose
B. 12:00 PM, at the midpoint between doses
C. 8:00 PM, exactly 24 hours after the last dose
D. Immediately after the morning dose is administered
Rationale: Trough levels for phenytoin are drawn immediately before the next
scheduled dose to measure the lowest drug concentration. Drawing at peak (after
dosing) or midpoint provides different clinical information and could lead to
inappropriate dosing adjustments.
Correct Answer: A
Q8. During a venipuncture, the phlebotomist notices the blood is bright red and
appears to be flowing under pressure rather than by vacuum. What is the most likely
explanation?
A. The needle has penetrated through the vein into an artery
B. The patient is severely anemic
C. The tube additive has activated prematurely
D. The tourniquet was applied for less than 1 minute
Rationale: Arterial blood is bright red (high oxygen content) and flows under
pressure due to arterial blood pressure, unlike venous blood which flows by vacuum.
This is a serious complication requiring immediate needle withdrawal and prolonged
pressure application.
Correct Answer: A
A-Graded Q&A | CLSI/OSHA/NHA Standards | Pass
Guaranteed - A+ Graded
Section 1: Phlebotomy Procedures & Venipuncture Techniques
(Q1-22)
Q1. A phlebotomist is preparing to collect a complete blood count (CBC),
comprehensive metabolic panel (CMP), and prothrombin time (PT) from a patient.
According to the 2026 CLSI order of draw guidelines, which tube should be drawn
first?
A. Red top (no additive)
B. Light blue top (sodium citrate)
C. Green top (heparin)
D. Lavender top (EDTA)
Rationale: The light blue top (sodium citrate) for coagulation studies must be drawn
first when blood cultures are not ordered, as it is the most sensitive to tissue
thromboplastin contamination. Drawing EDTA or heparin first could contaminate
subsequent coagulation tubes and cause falsely prolonged clotting times.
Correct Answer: B
Q2. A patient presents for a fasting lipid panel and fasting glucose. The phlebotomist
notices the patient is drinking black coffee. Which action is most appropriate?
A. Proceed with the draw; black coffee does not affect fasting status
B. Cancel both tests and reschedule for another day
C. Proceed with the lipid panel but cancel the glucose test
D. Document the coffee intake and notify the ordering provider before proceeding
,Rationale: Black coffee without additives does not significantly affect fasting glucose
or lipid results, but proper documentation ensures transparency. Rescheduling is
unnecessary for black coffee, though cream/sugar would invalidate fasting status.
Correct Answer: A
Q3. During a routine venipuncture using a straight needle and holder, the
phlebotomist feels a "pop" as the needle enters the vein but no blood flows into the
tube. The bevel is fully within the vein. What is the most likely cause?
A. The needle angle is too steep
B. The tube vacuum has been lost
C. The tourniquet was applied too tightly
D. The patient has collapsed veins
Rationale: When the bevel is fully within the vein but no blood flows, the most
common cause is loss of tube vacuum, which can occur with expired tubes or if the
tube was previously punctured. A steep angle or collapsed veins would typically
prevent entry sensation.
Correct Answer: B
Q4. A phlebotomist is using a butterfly needle with a 12-inch tubing extension to
collect a light blue top and then a lavender top. According to CLSI guidelines, what
must be done to ensure proper additive-to-blood ratios?
A. Draw a discard tube before the light blue top
B. Invert the light blue top 8-10 times immediately after collection
C. Use a syringe instead of vacuum tubes
D. Apply the tourniquet only during the first tube fill
Rationale: When using butterfly systems with tubing extensions, a non-additive
discard tube must be drawn first to clear the air from the tubing; otherwise, the light
blue top will be underfilled, resulting in an incorrect 9:1 blood-to-citrate ratio.
,Inversion is important but does not address the underfill issue.
Correct Answer: A
Q5. A phlebotomist is preparing to draw blood from an obese patient whose
antecubital veins are not palpable. The patient states previous successful draws were
from the dorsal hand veins. Which equipment modification is most appropriate?
A. Use a 23-gauge butterfly needle with a warming pack
B. Use a 21-gauge straight needle with a standard tourniquet
C. Use a 25-gauge butterfly needle without a tourniquet
D. Use an 18-gauge straight needle with a blood pressure cuff
Rationale: Dorsal hand veins in obese patients are typically small and fragile; a 23-
gauge butterfly needle minimizes trauma while a warming pack promotes
vasodilation. A 21-gauge needle is too large for hand veins, and a 25-gauge may
cause hemolysis in certain tests.
Correct Answer: A
Q6. A phlebotomist draws a blood culture set from a patient with suspected sepsis.
The first bottle shows growth within 8 hours, while the second bottle remains
negative. Which pre-analytical error most likely explains this discrepancy?
A. Inadequate skin antisepsis leading to contamination of the first bottle
B. Drawing the aerobic bottle before the anaerobic bottle
C. Using a 23-gauge needle instead of a 21-gauge needle
D. Filling both bottles to exactly 10 mL each
Rationale: Rapid growth in only one bottle of a blood culture set strongly suggests
skin flora contamination due to inadequate antisepsis. The correct order is aerobic
then anaerobic, but order reversal would not cause selective growth. Needle gauge
and exact fill volumes do not explain this pattern.
Correct Answer: A
, Q7. A patient requires a therapeutic drug monitoring (TDM) draw for phenytoin at
trough level. The patient received their last dose at 8:00 PM yesterday. When should
the blood be drawn?
A. 6:00 AM, before the next scheduled dose
B. 12:00 PM, at the midpoint between doses
C. 8:00 PM, exactly 24 hours after the last dose
D. Immediately after the morning dose is administered
Rationale: Trough levels for phenytoin are drawn immediately before the next
scheduled dose to measure the lowest drug concentration. Drawing at peak (after
dosing) or midpoint provides different clinical information and could lead to
inappropriate dosing adjustments.
Correct Answer: A
Q8. During a venipuncture, the phlebotomist notices the blood is bright red and
appears to be flowing under pressure rather than by vacuum. What is the most likely
explanation?
A. The needle has penetrated through the vein into an artery
B. The patient is severely anemic
C. The tube additive has activated prematurely
D. The tourniquet was applied for less than 1 minute
Rationale: Arterial blood is bright red (high oxygen content) and flows under
pressure due to arterial blood pressure, unlike venous blood which flows by vacuum.
This is a serious complication requiring immediate needle withdrawal and prolonged
pressure application.
Correct Answer: A
