MLS Clinical Procedures & Protocols 3 — Questions and Answers
Question 1: Which quality control rule is violated when two consecutive QC values fall more than 2 standard deviations from the mean on the same side?
- Westgard 1-3s rule
- Westgard 2-2s rule (Correct answer)
- Westgard R-4s rule
- Westgard 1-2s warning rule
Correct answer: Westgard 2-2s rule
The 2-2s rule is violated when two consecutive controls exceed ±2 SD in the same direction, signaling a systematic error.
Question 2: A lab receives a request for a STAT troponin on a patient in the ED. The tube arrives unlabeled. What should the MLS do?
- Label it using the requisition and process immediately
- Call the ED to verify and relabel, then process if confirmed
- Reject the specimen and document per policy (Correct answer)
- Process the test and document the discrepancy afterward
Correct answer: Reject the specimen and document per policy
Unlabeled specimens must be rejected per CLSI and accreditation standards because mislabeling errors can cause patient harm; the ED must recollect with proper labeling.
Question 3: What does a corrected reticulocyte count (reticulocyte production index, RPI) below 2 indicate?
- Adequate bone marrow response to anemia
- Hypoproliferative or ineffective erythropoiesis (Correct answer)
- Hemolytic process with increased RBC destruction
- Polycythemia vera with erythroid hyperplasia
Correct answer: Hypoproliferative or ineffective erythropoiesis
An RPI <2 suggests the bone marrow is not producing enough red cells to compensate for anemia, pointing to hypoproliferative or ineffective erythropoiesis.
Question 4: When performing a Gram stain, decolorization with acetone-alcohol is the most critical step. Over-decolorization will cause:
- Gram-positive organisms to appear purple
- Gram-negative organisms to appear purple
- Gram-positive organisms to appear pink/red (Correct answer)
- No change because the safranin counterstain corrects this
Correct answer: Gram-positive organisms to appear pink/red
Over-decolorization removes the crystal violet-iodine complex from gram-positive organisms, causing them to stain pink with safranin and appear false gram-negative.
Question 5: A 24-hour urine is received for creatinine clearance. The volume is 850 mL. The serum creatinine is 1.2 mg/dL and the urine creatinine is 90 mg/dL. The patient weighs 70 kg and is 175 cm tall (BSA 1.8 m²). What should the MLS check FIRST before calculating clearance?
- Verify the specimen was kept refrigerated during collection
- Confirm the collection start and end times are documented (Correct answer)
- Repeat the serum creatinine on a new specimen
- Check if the patient took any nephrotoxic drugs
Correct answer: Confirm the collection start and end times are documented
Accurate timed collection is the most common source of error; without verified start and stop times, the volume cannot be correctly interpreted.
Question 6: Which blood component is stored at 20–24°C with continuous agitation?
- Packed red blood cells
- Fresh frozen plasma
- Cryoprecipitate
- Platelets (Correct answer)
Correct answer: Platelets
Platelets must be stored at room temperature (20–24°C) with continuous gentle agitation to prevent aggregation and maintain viability for up to 5–7 days.
Question 7: A cerebrospinal fluid specimen arrives with three tubes numbered 1, 2, and 3. Which tube should be sent to microbiology for culture?
- Tube 1, because it has the freshest sample
- Tube 2, because it is the cleanest for cell counts
- Tube 3, because it is least likely to be contaminated with skin flora from the tap (Correct answer)
- Any tube, because all CSF tubes are equivalent for culture
Correct answer: Tube 3, because it is least likely to be contaminated with skin flora from the tap
Tube 3 is sent for culture because later tubes are less likely to be contaminated with skin organisms introduced at the time of the lumbar puncture.
