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CLT8 practice questions

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Question 1Specimen Collection and Handling

A phlebotomist is about to collect a specimen for a coagulation panel (PT/INR and aPTT). Which tube should be drawn and in what order relative to other tubes?

  1. Lavender EDTA tube, filled first to preserve platelets
  2. Light blue sodium citrate tube, filled before any serum tube Correct answer.
  3. Light blue sodium citrate tube, filled after the serum tube
  4. Red serum tube, filled after the citrate tube

Explanation

Coagulation testing requires a light blue tube containing sodium citrate, and the tube must be filled to the marked line to maintain the correct 9:1 blood-to-anticoagulant ratio. Order of draw places the citrate tube before serum tubes so no additive carryover occurs, and the discard or serum tube comes later.

Question 2Specimen Collection and Handling

A blood culture set is ordered for an adult patient. What is the standard collection practice for maximizing recovery of organisms?

  1. Collect one set from the line and one set from the same vein immediately after
  2. Collect two sets from two separate venipuncture sites before antimicrobial therapy begins Correct answer.
  3. Collect both sets from a single venipuncture using the same needle
  4. Collect a single aerobic bottle only to reduce contamination

Explanation

Blood culture yield is greatest when at least two sets are collected from separate venipuncture sites, ideally before antibiotics are started. Separate sites help distinguish true bacteremia from skin-flora contamination and increase detection of intermittent bacteremia.

Question 3Specimen Collection and Handling

A 24-hour urine collection for creatinine clearance is being set up. Which instruction is essential to give the patient?

  1. Collect only the overnight voids and stop at breakfast
  2. Collect the first void of the morning and discard all subsequent voids
  3. Discard the first void and collect all urine thereafter until the 24-hour mark, keeping it refrigerated Correct answer.
  4. Collect a midstream sample each time and pool only those portions

Explanation

A timed collection begins by discarding the first void so that the interval starts with an empty bladder, then all urine produced during the timed period is saved, including the final void at the endpoint. Refrigeration or appropriate preservative prevents analyte degradation during the collection.

Question 4Specimen Collection and Handling

A capillary blood gas specimen is being collected from a heel puncture on a neonate. Which practice best ensures a valid result?

  1. Collect the sample in a plain microtainer and transport it on ice for one hour
  2. Puncture the central pad of the heel and allow the blood to clot before analysis
  3. Squeeze the heel firmly and repeatedly to speed collection
  4. Warm the heel, puncture the lateral aspect, and fill the heparinized capillary tube without air bubbles Correct answer.

Explanation

Heel puncture should be performed on the lateral or medial plantar surface, avoiding the calcaneus and central pad, after warming to increase perfusion. The heparinized tube must be filled completely and sealed without air bubbles, since air alters pH and gas measurements.

Question 5Specimen Collection and Handling

A phlebotomist must collect blood from an arm with a running IV line in the antecubital fossa. What is the most appropriate action?

  1. Collect from the opposite arm; if unavoidable, draw below the IV site after the line is stopped briefly Correct answer.
  2. Collect from the same arm directly above the IV site without stopping the infusion
  3. Collect from the IV line after flushing it with saline
  4. Collect from the same arm below the IV site while the infusion continues

Explanation

Specimens should be drawn from the arm without an IV whenever possible. If the only available site is the IV arm, the line should be temporarily stopped and the sample drawn distal to the IV site to avoid dilution by infusate.

Question 6Specimen Collection and Handling

A specimen for serum potassium is collected in a tube with a lavender stopper and transported without separation. Which preanalytical problem is most likely?

  1. Falsely elevated calcium from EDTA binding
  2. No effect, since EDTA preserves electrolytes
  3. Falsely decreased potassium from anticoagulant dilution
  4. Falsely elevated potassium from hemolysis and prolonged contact with EDTA Correct answer.

Explanation

EDTA tubes are intended for hematology, and their potassium EDTA content can raise measured potassium when the sample is used for chemistry. Prolonged contact and hemolysis further increase potassium because it is released from red cells.

Question 7Specimen Collection and Handling

A urine specimen for routine culture cannot reach the laboratory within one hour. What is the recommended handling?

  1. Store it in a warm incubator to preserve fastidious organisms
  2. Freeze the specimen at minus 20 degrees Celsius until transport
  3. Leave it at room temperature and add a preservative tablet at the lab
  4. Refrigerate the specimen at 2 to 8 degrees Celsius and deliver it as soon as possible Correct answer.

Explanation

When transport delay is unavoidable, urine should be refrigerated at 2 to 8 degrees Celsius to slow bacterial overgrowth that can produce a false-positive culture. Prompt delivery remains the goal, and refrigeration should be documented.

Question 8Specimen Collection and Handling

A stool specimen is being collected for detection of ova and parasites. Which collection practice is correct?

  1. Collect a urine sample since parasites are excreted in urine
  2. Collect a rectal swab and transport it dry at room temperature
  3. Allow the stool to sit at room temperature for 24 hours before transport
  4. Collect fresh stool in a clean container and submit it promptly, or place it in a preservative vial if transport is delayed Correct answer.

Explanation

Ova and parasite examinations require fresh stool submitted promptly or preserved in an appropriate fixative to maintain trophozoite morphology. Delay without preservative allows organisms to degenerate and reduces detection.

Question 9Specimen Collection and Handling

A sputum specimen is ordered for bacterial culture. Which collection method yields the most useful specimen?

  1. Saliva collected by spitting into a cup
  2. Throat swab collected after a mouth rinse
  3. Nasal swab collected from the anterior nares
  4. Deep cough specimen collected after rinsing the mouth, submitted in a sterile container Correct answer.

Explanation

A deep cough specimen is needed to obtain lower respiratory secretions rather than oral contamination. Rinsing the mouth reduces saliva and food residue, and a sterile container prevents introduction of organisms.

Question 10Specimen Collection and Handling

A blood specimen is drawn into a tube containing sodium citrate, but the tube is only half filled. How does this affect aPTT results?

  1. The aPTT is unaffected because citrate does not influence clotting time
  2. The aPTT is falsely prolonged because the citrate-to-blood ratio is excessive Correct answer.
  3. The aPTT is falsely prolonged because calcium is added in excess
  4. The aPTT is falsely shortened because more anticoagulant is present

Explanation

Underfilled citrate tubes contain too much anticoagulant relative to plasma, which binds calcium and prolongs clotting times. The tube must be filled to the indicated line to preserve the 9:1 ratio.

Question 11Specimen Collection and Handling

A skin puncture is planned for a fingerstick glucose on an adult. Which site is preferred?

  1. The tip of the thumb
  2. The earlobe
  3. The center of the fingertip pad
  4. The side of the fingertip, avoiding the pad center Correct answer.

Explanation

The lateral aspect of the fingertip has fewer nerve endings and less callus, reducing pain and improving blood flow. The central pad is more sensitive and should be avoided.

Question 12Specimen Collection and Handling

A laboratory receives a pleural fluid specimen in a plain tube for cell count and differential. What is the primary concern?

  1. The plain tube is ideal because EDTA interferes with cell counts
  2. The specimen should be frozen before counting
  3. The specimen should be diluted with saline to prevent clotting
  4. Cells may clump or lyse, so an EDTA tube should have been used for the cell count Correct answer.

Explanation

Body fluid cell counts are best performed on an anticoagulated specimen, typically EDTA, because clotting and cell degeneration distort counts and differentials. A plain tube risks clumping that makes the count unreliable.

Question 13Specimen Collection and Handling

A patient reports fainting during previous blood draws. Which precaution is most appropriate before the venipuncture?

  1. Perform the draw quickly without any monitoring
  2. Position the patient reclining or supine and observe closely during and after the draw Correct answer.
  3. Have the patient stand and hold a chair for support
  4. Ask the patient to hyperventilate before the draw

Explanation

Patients with a history of syncope should be positioned so that a fall is prevented, ideally reclining or supine, and observed throughout and briefly afterward. This reduces injury risk if vasovagal syncope occurs.

Question 14Specimen Collection and Handling

A specimen for ammonia is collected and left at room temperature for two hours before analysis. What is the expected effect?

  1. Ammonia will be falsely decreased because it evaporates
  2. Ammonia will be falsely elevated because red cells continue to produce it Correct answer.
  3. Ammonia will be unchanged because it is stable at room temperature
  4. Ammonia will be falsely elevated only if the tube is heparinized

Explanation

Ammonia is unstable in whole blood, and continued red cell metabolism releases ammonia, causing falsely high results. The specimen should be placed on ice and separated promptly to minimize this preanalytical error.

Question 15Specimen Collection and Handling

A blood donor tube for a hematocrit must be collected. Which tube and handling are appropriate?

  1. Red clot tube, centrifuged immediately without mixing
  2. Light blue citrate tube, filled to half volume
  3. Gray fluoride tube, mixed vigorously to preserve cells
  4. Lavender EDTA tube, mixed gently and analyzed before cells settle Correct answer.

Explanation

Hematology testing requires an EDTA tube to preserve cell morphology, and gentle mixing prevents clotting without hemolysis. Prompt analysis avoids cell settling that can distort counts.

Question 16Specimen Collection and Handling

A patient is receiving a heparin infusion, and a specimen is collected from the arm with the IV. Which statement best describes the preanalytical risk?

  1. The specimen may be contaminated with heparin, falsely prolonging clotting times Correct answer.
  2. Heparin has no effect on coagulation testing
  3. The specimen will be falsely hemolyzed by heparin
  4. The specimen may be contaminated with heparin, falsely shortening clotting times

Explanation

Blood drawn near or from an IV line carrying heparin can be contaminated with the drug, which inhibits clotting and falsely prolongs aPTT and related tests. Collection from the opposite arm or careful line management is required.

Question 17Specimen Collection and Handling

A specimen for lactic acid is collected in a gray-top tube. Why is this tube chosen?

  1. The gray stopper indicates the tube must be kept warm
  2. Sodium fluoride lyses red cells to release lactate
  3. The tube contains EDTA to stabilize lactate
  4. Sodium fluoride inhibits glycolysis, limiting further lactate production Correct answer.

Explanation

Sodium fluoride in gray-top tubes inhibits glycolysis, slowing the continued production of lactate by cells after collection. Prompt processing and appropriate transport further protect the result.

Question 18Specimen Collection and Handling

A 24-hour urine specimen is accidentally collected without discarding the first morning void. What is the most appropriate action?

  1. Analyze the specimen and document the error on the report
  2. Refrigerate the specimen and analyze it without correction
  3. Discard the collection and restart the timed interval correctly Correct answer.
  4. Add the missed void volume from the patient's estimate

Explanation

Including the first void adds urine produced before the timed interval began, which overestimates the analyte amount for the collection period. The proper response is to discard the collection and restart with correct instructions.

Question 19Specimen Collection and Handling

A laboratory receives a specimen in a tube whose stopper is cracked, and the tube is leaking. What should be done first?

  1. Discard the label and relabel the tube with a new number
  2. Treat it as a biohazard, contain the leak, and reject the specimen for replacement Correct answer.
  3. Open the tube to check the contents and then analyze it
  4. Wipe the tube and place it directly on the analyzer

Explanation

A leaking or cracked tube is a biohazard and an integrity failure, so it must be contained safely and the specimen rejected. The collection should be repeated, and the incident handled per exposure-control procedures.

Question 20Specimen Collection and Handling

A patient has an order for a glucose tolerance test. Which instruction is correct for the fasting specimen?

  1. The patient should fast for 8 to 12 hours and a fasting glucose is drawn before the glucose load Correct answer.
  2. The patient should drink the glucose solution before the fasting specimen
  3. The patient should fast for 24 hours before the test
  4. The patient should eat a normal breakfast before the fasting draw

Explanation

A glucose tolerance test requires an 8- to 12-hour fast, and the baseline fasting specimen is drawn before the glucose load is administered. Timing of subsequent specimens follows the protocol.

Question 21Specimen Collection and Handling

A sputum specimen for acid-fast bacilli is being collected. Which practice is most important?

  1. Collect a throat swab instead of sputum
  2. Collect the specimen after starting antibiotics to reduce contamination
  3. Collect early-morning deep-cough specimens on consecutive days in a sterile container Correct answer.
  4. Collect a single saliva sample and transport it at room temperature

Explanation

AFB testing benefits from early-morning deep-cough specimens collected on consecutive days to increase yield. Specimens should be collected before or independent of antibiotic therapy and submitted in sterile containers.

Question 22Specimen Collection and Handling

A newborn screening specimen is collected by heel puncture on filter paper. Which action is required?

  1. Allow the card to remain wet and transport it immediately
  2. Collect the specimen from the central heel pad
  3. Apply multiple small drops to each circle to save time
  4. Fill the circles completely with blood and allow them to dry before transport Correct answer.

Explanation

Newborn screening cards must be saturated with a single continuous application of blood so the circles are completely filled, then air-dried before transport to preserve analyte stability. Layering drops can cause uneven saturation and invalid results.

Question 23Specimen Collection and Handling

A specimen for a cold agglutinin test is collected. What handling is required?

  1. Allow the specimen to clot at refrigerator temperature
  2. Keep the specimen warm and transport it promptly to the laboratory Correct answer.
  3. Freeze the specimen until analysis
  4. Place the specimen on ice immediately after collection

Explanation

Cold agglutinins cause red cells to clump at low temperatures, which can falsely lower counts and distort results. The specimen must be kept warm and delivered promptly so the agglutination does not occur before testing.

Question 24Specimen Collection and Handling

A phlebotomist collects a specimen for a therapeutic drug level and documents the draw time. Why is the timing record critical?

  1. Timing only matters for urine drug testing
  2. The tube type changes with the time of day
  3. Drug concentrations vary with dosing intervals, so interpretation depends on the time relative to the dose Correct answer.
  4. The specimen must be drawn at a fixed clock time regardless of dosing

Explanation

Therapeutic drug monitoring interprets concentrations relative to the dosing schedule, such as peak or trough levels. Accurate documentation of the collection time allows the result to be compared with the appropriate reference point.

Question 25Specimen Collection and Handling

A specimen is collected for a blood culture from a patient who has been on antibiotics for two days. What is the best guidance?

  1. Delay the culture until the patient is discharged
  2. Collect the culture as ordered and note the antibiotic therapy, since yield may be reduced Correct answer.
  3. Skip the culture because antibiotics make it useless
  4. Draw a single aerobic bottle to reduce cost

Explanation

Antibiotic therapy can reduce the number of viable organisms, but cultures are still collected as ordered with the therapy documented so the laboratory and clinician can interpret results appropriately. Collection before the next dose may improve yield.

Question 26Specimen Collection and Handling

A blood specimen is collected into a tube with a light blue stopper for coagulation testing. The phlebotomist fills the tube to the indicated mark and mixes it immediately. Which statement explains why the fill volume and mixing are critical?

  1. The tube contains EDTA, so underfilling causes excess EDTA that falsely elevates calcium and shortens clotting times.
  2. The tube contains a fixed amount of citrate, so underfilling causes excess citrate that binds calcium and falsely prolongs clotting times. Correct answer.
  3. The tube contains heparin, so underfilling causes excess heparin that falsely shortens clotting times.
  4. The tube contains no additive, so fill volume only affects the serum yield and not the test result.

Explanation

Light blue tubes contain a fixed volume of sodium citrate, which chelates calcium. The tube must be filled to the indicated mark so the blood-to-additive ratio is correct; underfilling leaves excess citrate that binds calcium and falsely prolongs clotting times. Immediate mixing ensures the citrate is distributed evenly and prevents microclots.

Question 27Specimen Collection and Handling

A laboratory receives a blood specimen for a fasting glucose test. The tube was collected in a gray-top tube and centrifuged within 30 minutes. Which statement best explains the purpose of the gray-top tube in this context?

  1. The gray top contains sodium fluoride, which inhibits glycolysis and preserves glucose concentration. Correct answer.
  2. The gray top contains citrate, which chelates calcium and preserves glucose concentration.
  3. The gray top contains heparin, which accelerates glycolysis and preserves glucose concentration.
  4. The gray top contains EDTA, which prevents clotting and preserves glucose concentration.

Explanation

Gray-top tubes contain sodium fluoride, an antiglycolytic agent that inhibits the enzyme enolase and stops glycolysis, preserving glucose levels. Without fluoride, glucose in whole blood decreases over time due to cellular metabolism. Centrifugation within 30 minutes also helps separate cells from serum or plasma.

Question 28Specimen Collection and Handling

A phlebotomist is performing a venipuncture on a patient with a history of syncope. After the draw, the patient reports feeling lightheaded and dizzy. Which action is most appropriate?

  1. Have the patient sit up quickly and drink a glass of water.
  2. Lower the patient's head and apply a cold compress to the forehead.
  3. Apply a bandage and escort the patient to the waiting room to lie down.
  4. Place the patient in a supine position with legs elevated and monitor vital signs. Correct answer.

Explanation

For a patient with syncope during or after venipuncture, the priority is to prevent injury from a fall. Place the patient supine with legs elevated to promote venous return to the heart and brain, and monitor vital signs. Do not allow the patient to sit up or walk immediately.

Question 29Specimen Collection and Handling

A 24-hour urine collection is being performed for creatinine clearance. The patient calls the laboratory at 10:00 AM on day 2 to report that the first morning void was accidentally discarded instead of being collected. What is the most appropriate instruction?

  1. Collect an additional 24-hour specimen immediately after the current one ends.
  2. Continue the collection as planned and note the error on the requisition.
  3. Discard the entire collection and restart the 24-hour period tomorrow morning. Correct answer.
  4. Add the discarded void volume to the collection container and continue.

Explanation

A 24-hour urine collection must include all urine produced during the exact time period. If the first morning void is discarded, the collection is incomplete and the results will be inaccurate. The correct action is to discard the current collection and restart the 24-hour period with the next morning's first void.

Question 30Specimen Collection and Handling

A blood specimen for ammonia is collected in an EDTA tube and transported on ice to the laboratory. The laboratory rejects the specimen. Which preanalytical error is the most likely reason for rejection?

  1. Ammonia is stable at room temperature, so icing the specimen causes falsely low results.
  2. EDTA interferes with the ammonia assay, and the specimen should have been collected in a heparin tube. Correct answer.
  3. The specimen should have been collected in a sodium citrate tube to prevent clotting.
  4. Ammonia requires immediate separation and freezing of the plasma, which was not done.

Explanation

Ammonia testing requires a heparinized tube (green top) because EDTA can interfere with the assay and cause falsely elevated results. Additionally, ammonia specimens should be placed on ice and separated quickly to prevent false elevation from red cell metabolism. Collecting in EDTA is a preanalytical error that warrants rejection.

Question 31Quality Control and Quality Assurance

In a clinical laboratory quality programme, which document defines the quality control procedures, acceptance criteria, and corrective actions for each analytical method?

  1. The safety data sheet
  2. The instrument purchase order
  3. The quality control plan Correct answer.
  4. The personnel training roster

Explanation

A quality control plan specifies, for each method, the control materials, frequency of testing, acceptance limits, and the actions taken when results fall outside limits. It is the operational document that links QC performance to corrective action. Other documents serve safety, procurement, or staffing purposes.

Question 32Quality Control and Quality Assurance

A laboratory plots daily control values on a Levey-Jennings chart. Which feature of the chart allows detection of a systematic shift in method performance?

  1. The colour coding of the chart background
  2. The control limits drawn at plus and minus two standard deviations
  3. The pattern of consecutive points on one side of the mean Correct answer.
  4. The date printed in the chart header

Explanation

A systematic shift appears as a run of consecutive points on the same side of the mean, which is a trend or shift rule violation. Control limits define the spread of acceptable random variation but do not by themselves reveal a sustained bias. Background colour and header date carry no analytical meaning.

Question 33Quality Control and Quality Assurance

Which statement best describes the purpose of an external quality assessment (proficiency testing) scheme?

  1. It documents staff attendance at continuing education sessions
  2. It calibrates the analyser using the manufacturer's master curve
  3. It replaces the need for internal quality control on routine patient samples
  4. It verifies that a laboratory's results agree with those of peer laboratories on the same unknown sample Correct answer.

Explanation

External quality assessment compares a laboratory's result on an unknown specimen with the consensus or assigned value from peer laboratories, providing an independent check on accuracy. It is complementary to internal QC and does not replace daily control testing. It also does not perform instrument calibration or record training attendance.

Question 34Quality Control and Quality Assurance

In a quality management system, which activity is an example of quality assurance rather than quality control?

  1. Testing a control material with each analytical run
  2. Repeating a patient sample because the result exceeded the control limit
  3. Recording the control value on the daily worksheet
  4. Reviewing audit findings to revise a specimen-handling procedure Correct answer.

Explanation

Quality assurance is the planned, systematic activity that ensures processes are designed and improved to meet quality requirements, such as acting on audit findings to revise procedures. Quality control is the operational testing of samples and controls to detect errors in individual runs. Repeating samples and recording control values are QC activities.

Question 35Quality Control and Quality Assurance

A laboratory receives a control material with an assayed value and an uncertainty statement. What is the most appropriate use of this information when establishing control limits?

  1. Use the assayed value as the target mean and derive limits from the laboratory's own observed standard deviation Correct answer.
  2. Discard the assayed value and set the target mean to zero
  3. Adopt the manufacturer's stated range as the control limits without further study
  4. Use the uncertainty value as the sole acceptance criterion for patient results

Explanation

The assayed value provides a target mean, but control limits should reflect the laboratory's own observed imprecision, usually from at least 20 data points. Manufacturer ranges are too wide or not representative of local performance. The uncertainty statement does not define patient-result acceptance criteria.

Question 36Quality Control and Quality Assurance

A single control observation falls beyond plus three standard deviations on a Levey-Jennings chart. According to common Westgard multirule logic, what is the appropriate first action?

  1. Ignore the point because it is an isolated outlier
  2. Reject the run and investigate for random error before reporting results Correct answer.
  3. Report patient results because only one control point is outside limits
  4. Recalibrate the instrument and immediately release all results

Explanation

A single control value exceeding three standard deviations is a 1-3s violation and signals unacceptable random error, so the run should be rejected and investigated. Patient results should not be reported until the cause is identified and corrected. Immediate release or dismissal of the point would risk reporting erroneous results.

Question 37Quality Control and Quality Assurance

Four consecutive control measurements fall on the same side of the mean but within two standard deviations. Which Westgard rule is violated and what type of error does it suggest?

  1. 1-2s rule, suggesting random error
  2. R-4s rule, suggesting random error
  3. 10x rule, suggesting a trend in calibration
  4. 4-1s rule, suggesting systematic error Correct answer.

Explanation

The 4-1s rule flags four consecutive control values on one side of the mean, which indicates a systematic shift such as a calibration drift or reagent lot change. A 1-2s violation involves a single value beyond two SD. The R-4s rule concerns the range between two controls, and the 10x rule requires ten consecutive values.

Question 38Quality Control and Quality Assurance

Which practice best supports traceability of measurement results in a clinical laboratory?

  1. Averaging duplicate patient results to reduce imprecision
  2. Using the same reagent lot indefinitely to avoid variation
  3. Comparing results with a neighbouring laboratory once per year
  4. Calibrating against reference materials with values assigned by a higher-order reference method Correct answer.

Explanation

Metrological traceability is established through an unbroken chain of calibrations to higher-order reference materials or methods, ideally certified reference materials. Peer comparison and lot consistency do not establish traceability. Averaging duplicates reduces random error but does not link results to a reference.

Question 39Quality Control and Quality Assurance

A laboratory documents that a reagent lot change caused a shift in control values. Which element of the quality system is being exercised when the laboratory investigates, corrects, and records the event?

  1. Preventive maintenance scheduling
  2. Competency assessment of technical staff
  3. Corrective action within nonconforming event management Correct answer.
  4. Proficiency testing enrolment

Explanation

Investigating a nonconformance, identifying its root cause, and implementing and recording a correction is corrective action management. Preventive maintenance addresses equipment upkeep before failure. Competency assessment and proficiency testing are separate quality activities.

Question 40Quality Control and Quality Assurance

What is the primary purpose of a root cause analysis following a significant quality failure?

  1. To satisfy the annual audit checklist without further action
  2. To identify underlying system causes so that recurrence is prevented Correct answer.
  3. To assign blame to the individual who performed the test
  4. To reduce the number of quality records retained

Explanation

Root cause analysis seeks the underlying process or system failures that allowed an error to occur, so that effective corrective and preventive actions can stop recurrence. It is not a disciplinary tool and should focus on systems rather than individuals. Completing checklists or reducing records does not address the cause.

Question 41Quality Control and Quality Assurance

A laboratory wants to estimate the imprecision of a new method before introducing it. Which approach is most appropriate?

  1. Test a pooled patient sample repeatedly over several days and calculate the coefficient of variation Correct answer.
  2. Use the calibration certificate uncertainty as the imprecision value
  3. Ask two technologists to estimate the variation by eye
  4. Test a single sample once and compare it with the manufacturer's claim

Explanation

Replicate testing of a stable sample over multiple days captures within-run and between-run variation, and the coefficient of variation expresses relative imprecision. A single measurement cannot estimate variation. Subjective estimation and calibration uncertainty do not measure method imprecision.

Question 42Quality Control and Quality Assurance

In a quality control chart, which change would increase the probability of detecting a small systematic shift?

  1. Removing the mean line from the chart
  2. Increasing the number of control observations per run and applying multirule criteria Correct answer.
  3. Reducing the frequency of control testing to once per week
  4. Widening the control limits to plus and minus four standard deviations

Explanation

More control observations and multirule criteria increase the sensitivity to small shifts while keeping false rejection acceptable. Widening limits or reducing testing frequency lowers error detection. Removing the mean line eliminates the reference needed to spot a shift.

Question 43Quality Control and Quality Assurance

Which of the following is the best example of a pre-analytical quality indicator in a clinical laboratory?

  1. Turnaround time for reporting a critical result after analysis
  2. Between-run coefficient of variation for a chemistry analyte
  3. Percentage of specimens rejected for insufficient volume or incorrect tube type Correct answer.
  4. Number of calibrations performed per month

Explanation

Pre-analytical indicators measure events before analysis, such as specimen collection, transport, and acceptability, including rejection rates for volume or tube type. Imprecision and calibration frequency relate to the analytical phase. Critical result reporting occurs after analysis.

Question 44Quality Control and Quality Assurance

A laboratory records a corrected report after discovering a transcription error in a patient result. Which quality activity does this documentation primarily support?

  1. Method validation
  2. Preventive maintenance of the analyser
  3. Post-analytical error monitoring and corrective action Correct answer.
  4. Reagent inventory control

Explanation

Detecting and correcting a reporting error is a post-analytical quality event, and documenting it supports monitoring and corrective action. Method validation, equipment maintenance, and inventory control belong to other phases of the quality system.

Question 45Quality Control and Quality Assurance

Which statement correctly distinguishes accuracy from precision?

  1. Accuracy describes closeness to the true value, while precision describes agreement among replicate measurements Correct answer.
  2. Precision can only be assessed with a certified reference material
  3. Accuracy describes agreement among replicates, while precision describes closeness to the true value
  4. Accuracy and precision are synonyms in laboratory quality control

Explanation

Accuracy reflects how close a result is to the true or assigned value, whereas precision reflects the closeness of repeated measurements to each other. A method can be precise but biased. Precision is assessed from replicate measurements and does not require a certified reference material.

Question 46Quality Control and Quality Assurance

A laboratory uses a moving average of patient results to monitor method stability. What is the main advantage of this approach?

  1. It replaces calibration of the analyser
  2. It provides continuous monitoring without additional control material consumption Correct answer.
  3. It directly assigns a reference value to the method
  4. It eliminates the need for any statistical control limits

Explanation

Patient-based moving averages allow frequent, continuous monitoring of method stability using routine specimens, reducing control material use. The technique still relies on statistical limits and does not assign reference values or replace calibration.

Question 47Quality Control and Quality Assurance

Which action is required when a laboratory's proficiency testing result is judged unacceptable for an analyte?

  1. Change the analyte reference interval to match the peer group
  2. Report the failure only at the next external audit
  3. Withdraw from the scheme to avoid further failures
  4. Investigate the cause, implement corrective action, and evaluate the effect on patient results Correct answer.

Explanation

An unacceptable proficiency testing result requires investigation of the root cause, corrective action, and assessment of whether patient results were affected. Withdrawing or delaying disclosure avoids the required improvement process. Altering reference intervals does not address analytical error.

Question 48Quality Control and Quality Assurance

In the context of analytical quality, which term describes the smallest change in analyte concentration that can be reliably distinguished from zero?

  1. Reference interval
  2. Limit of quantitation
  3. Total allowable error
  4. Limit of detection Correct answer.

Explanation

The limit of detection is the lowest analyte concentration that can be distinguished from a blank with a stated confidence. The limit of quantitation is the lowest level measurable with acceptable precision and accuracy. Reference intervals and total allowable error describe different concepts.

Question 49Quality Control and Quality Assurance

A laboratory wants to verify that a new analyser meets the manufacturer's claimed imprecision before routine use. Which approach is most defensible?

  1. Perform replicate measurements at clinically relevant concentrations and compare the observed CV with the claimed CV Correct answer.
  2. Ask the vendor representative to confirm performance verbally
  3. Run one patient sample and compare the result with the previous analyser
  4. Accept the manufacturer's claim without local verification

Explanation

Verification requires local replicate testing at clinically relevant levels and statistical comparison of observed imprecision with the manufacturer's claim. Single samples, unverified acceptance, and verbal assurances do not provide objective evidence of performance.

Question 50Quality Control and Quality Assurance

A control rule produces frequent false rejections without detecting real errors. What is the most likely consequence for laboratory operations?

  1. Increased repeat testing and delayed reporting, with staff becoming desensitised to alarms Correct answer.
  2. Lower total allowable error for the method
  3. Reduced need for calibration and maintenance
  4. Improved analytical accuracy from stricter limits

Explanation

Excessive false rejections cause unnecessary repeats and reporting delays and can lead staff to disregard genuine alarms. Stricter limits do not improve accuracy by themselves. Control rules do not affect calibration needs or the total allowable error specification.