MLT GlobeLaboratory Operations: Phlebotomy & specimen handling
42 Laboratory Operations MCQs on Phlebotomy & specimen handling with answers and explanations.
A heparinized syringe is the standard collection device for which specimen?
Blood gas samples are drawn arterially into syringes containing dry balanced heparin, which does not alter pH or ions. CBCs use EDTA and serum requires clotting.
To obtain serum rather than plasma, blood must be collected into which tube?
Serum is the fluid left after clotting consumes fibrinogen. Anticoagulated tubes yield plasma, which still contains fibrinogen.
Why is K2EDTA the anticoagulant of choice for a routine CBC?
EDTA chelates calcium and keeps cells well preserved for counting and smears. It does not bind iron as its anticoagulant action, and it is unsuitable for coagulation factor assays.
When transferring blood from a syringe into an EDTA tube, which practice best prevents a spurious result?
Correct fill ratio and gentle inversion ensure mixing without hemolysis. Forcing blood through a needle or shaking causes hemolysis; underfilling gives excess EDTA and cell shrinkage.
A clinician requests a CBC with blood film. Which tube should be drawn?
EDTA preserves cell counts and morphology. Citrate is for coagulation, heparin for chemistry (it causes platelet clumping and poor staining), and fluoride-oxalate for glucose.
For routine venipuncture, the vein of first choice in the antecubital fossa is the:
The median cubital vein is large, well anchored and away from major nerves and the brachial artery. The basilic vein lies near the artery and median nerve.
Serum differs from plasma because serum:
Serum is the fluid left after blood clots, so fibrinogen and factors V and VIII are consumed. Plasma comes from anticoagulated blood and retains them.
According to the CLSI order of draw, a collection requires blood culture, light blue, gold (SST), green, lavender and gray tubes. Which tube is drawn immediately before lavender?
CLSI order: blood culture, citrate, serum tubes, heparin, EDTA, then glycolytic inhibitor. So green (heparin) comes just before lavender; gray is last.
A 3.2% sodium citrate tube for PT and aPTT is received only half full. What effect is expected if it is tested?
The correct blood-to-citrate ratio is 9:1. Underfilling leaves excess citrate, which binds the added calcium in the test and falsely prolongs PT and aPTT.
Which antecubital vein is usually the first choice for routine venipuncture because it is large, well anchored and less painful?
The median cubital vein is well anchored and away from major nerves and arteries. The basilic vein lies near the brachial artery and median nerve, so it is the last choice.
A patient has an IV infusion running in the left forearm. The right arm has suitable veins. Where should blood be collected?
Blood should be drawn from the arm without the IV to avoid dilution and contamination by IV fluid. Drawing above an IV site is never acceptable.
During venipuncture, a seated patient becomes pale, sweaty and says she feels faint. The phlebotomist should first:
Stop the draw immediately, remove tourniquet and needle, apply pressure and lower the head or have the patient lie down. Ammonia inhalants are not recommended.
A neonatal bilirubin specimen is collected. Which special handling is required?
Bilirubin is broken down by light, which can lower the result by a significant amount within an hour. Use an amber tube or wrap it in foil.
Which statement about needle gauge is correct?
Gauge is inversely related to bore diameter: a 23 G needle is thinner than a 21 G needle. Routine adult venipuncture commonly uses 21–22 G; 16 G is used for blood donation.
During routine venipuncture, the needle should enter the vein at an angle of about:
An angle of about 15–30 degrees (bevel up) allows smooth vein entry without passing through the back wall. Steeper angles increase the risk of going through the vein.
Before collecting blood from an inpatient, the phlebotomist must positively identify the patient by:
At least two unique identifiers, checked against the wristband and request, are required. Room numbers are not identifiers, and a yes/no question may be answered wrongly by a confused patient.
A patient had a right mastectomy with removal of axillary lymph nodes. Where should blood be drawn without a doctor's permission?
The arm on the side of lymph node removal may have lymphoedema and infection risk, and results may be affected. The opposite arm is used unless a doctor approves otherwise.
The gel in a serum separator tube (SST) serves to:
The gel has a density between serum and cells, so it moves up to form a barrier during centrifugation.
Immediately after collection, an EDTA tube should be mixed by:
Gentle inversion mixes the anticoagulant without haemolysing cells; vigorous shaking causes haemolysis.
Blood collected in a plain or gel serum tube should be allowed to clot before centrifugation for about:
About 30 minutes at room temperature allows complete clotting; centrifuging too early leaves fibrin in the serum.