MLPAO - Medical Laboratory Professionals Association of Ontario Specimen Collection and Handling Questions and Answers 2 — Questions and Answers

Question 1: When performing venipuncture, the tourniquet should be removed from the patient's arm at what point?

Immediately after needle insertion
After the last tube has been filled and before needle removal (Correct answer)
Only after applying pressure to the site
Before inserting the needle to prevent hemoconcentration

Correct answer: After the last tube has been filled and before needle removal

The tourniquet should be released after the last tube is filled and before the needle is withdrawn to prevent hematoma formation and restore normal circulation.

Proper venipuncture technique requires removing the tourniquet before withdrawing the needle to prevent formation of a hematoma and to restore normal venous blood flow. The tourniquet should be in place no longer than 1 minute total, as prolonged application can cause hemoconcentration (falsely elevated protein, cell counts, and other analytes). The sequence is: insert needle, confirm blood flow, fill tubes in proper order, release tourniquet after the last tube begins filling, withdraw needle, apply pressure. This technique minimizes patient discomfort and pre-analytical errors.

Question 2: For a coagulation test such as PT/INR, which is the correct blood-to-anticoagulant ratio in a sodium citrate (blue top) tube?

5:1
9:1 (Correct answer)
3:1
1:9

Correct answer: 9:1

The correct blood-to-anticoagulant ratio for sodium citrate tubes used in coagulation testing is 9 parts blood to 1 part citrate (9:1).

Sodium citrate tubes (blue top) used for coagulation studies must be filled to exactly the correct volume to maintain the 9:1 blood-to-anticoagulant ratio. Under-filled tubes have excess citrate relative to plasma, which can prolong clotting times and produce falsely elevated PT/INR and APTT results. Over-filled tubes are not a concern since excess blood doesn't affect results as critically. For patients with polycythemia (high hematocrit >55%), reduced citrate volume is required because there is less plasma volume. Proper tube fill is a critical pre-analytical factor for coagulation testing quality.

Question 3: What is the correct order of draw when collecting blood in multiple tube types during a single venipuncture?

EDTA → Sodium Citrate → Serum Separator → Heparin
Blood Culture → Sodium Citrate → Serum → Heparin → EDTA → Glucose (Correct answer)
Serum → EDTA → Heparin → Sodium Citrate
Heparin → Serum → EDTA → Blood Culture

Correct answer: Blood Culture → Sodium Citrate → Serum → Heparin → EDTA → Glucose

The correct CLSI order of draw is: blood culture, sodium citrate (blue), serum/SST (red/gold), heparin (green), EDTA (purple), glucose/fluoride (grey).

The Clinical and Laboratory Standards Institute (CLSI) order of draw is established to prevent additive carryover between tubes, which can cause erroneous results. The correct order is: 1) Blood cultures (sterile technique), 2) Sodium citrate (blue — coagulation), 3) Serum or SST (red/gold — chemistry), 4) Lithium heparin (green — chemistry), 5) EDTA (purple — hematology), 6) Fluoride/oxalate (grey — glucose). EDTA contamination of coagulation tubes would cause falsely prolonged clotting times; citrate before serum prevents calcium contamination. This sequence is standardized across Ontario laboratory practice.

Question 4: A 2-year-old patient requires blood collection. Which specimen collection method is most appropriate?

Standard venipuncture from the antecubital fossa using a 21-gauge needle
Arterial puncture from the radial artery
Capillary puncture from the heel or fingertip using a lancet (Correct answer)
Central venous catheter access only

Correct answer: Capillary puncture from the heel or fingertip using a lancet

Capillary puncture is the preferred method for young children as it is less invasive, requires smaller volumes, and is appropriate for the types of tests typically ordered in pediatric patients.

In young children (typically under 2 years or those with difficult venous access), capillary (skin puncture) blood collection from the heel (neonates/infants) or fingertip (older children) is the preferred method. This approach requires smaller blood volumes, is less traumatic, and avoids the risks of large-needle venipuncture in small veins. The heel is used in neonates; the fingertip can be used in children old enough to have developed sufficient capillary bed. Antecubital fossa venipuncture with standard needles is inappropriate for toddlers. Arterial puncture is reserved for blood gas analysis only. CMLTO exam candidates must know pediatric collection protocols.

Question 5: Which of the following specimens requires protection from light during transport and storage?

Serum for calcium analysis
Whole blood for CBC
Serum or plasma for bilirubin analysis (Correct answer)
Urine for microalbumin

Correct answer: Serum or plasma for bilirubin analysis

Bilirubin is photosensitive and degrades rapidly when exposed to light. Specimens for bilirubin analysis must be protected from light during collection, transport, and storage.

Bilirubin (both total and direct fractions) is highly photosensitive and degrades by up to 50% within 1-2 hours of exposure to fluorescent or sunlight. Specimens for bilirubin analysis must be collected in amber-coloured tubes or wrapped in foil immediately after collection, kept protected during transport, and processed promptly. This is particularly critical in neonatal jaundice monitoring where bilirubin results guide clinical management decisions. Failure to protect bilirubin specimens from light is a common pre-analytical error that leads to falsely low results, potentially missing clinically significant hyperbilirubinemia.

Question 6: What is the maximum time a peripheral blood smear should be made after collecting an EDTA blood sample for accurate WBC differential?

Within 30 minutes of collection (Correct answer)
Within 1 hour of collection
Within 4 hours if refrigerated
Within 24 hours if stored at room temperature

Correct answer: Within 30 minutes of collection

Blood smears for WBC differential should ideally be made within 30 minutes of collection to prevent cellular morphology changes, particularly neutrophil lobulation and lymphocyte vacuolation.

Blood films for differential leukocyte counting and cellular morphology assessment should be prepared within 30 minutes of venipuncture (or from EDTA blood within 1 hour maximum). After collection, WBCs undergo progressive morphological changes: neutrophils develop hypersegmentation of nuclei (pseudo left shift), lymphocytes show vacuolation, and monocytes develop pseudopod extensions. These changes can lead to incorrect classification of cells and erroneous differential counts. If immediate smear preparation is not possible, specimens can be stored at 4°C and smears made within 4 hours, but room temperature storage accelerates deterioration.

MLPAO - Medical Laboratory Professionals Association of Ontario Specimen Collection and Handling Questions and Answers 2

When performing venipuncture, the tourniquet should be removed from the patient's arm at what point?