A laboratory's creatinine EQAS results over three cycles have SDIs of +2.4, +2.6 and +2.3, against a peer group using the same analyser and reagent (acceptable within ±2). Its internal QC, with limits set from its own data, has stayed within ±2 SD throughout. The most appropriate conclusion is:

A constant bias that internal QC cannot detect; check calibration

Peer group mismatch; change the comparison group

Poor precision; widen the internal QC limits

Random error on the EQAS samples; no action needed

A glucose method uses two controls: level 1 mean 100 mg/dL, SD 3 mg/dL; level 2 mean 300 mg/dL, SD 8 mg/dL. All previous runs were within ±1 SD. Today level 1 reads 107 mg/dL and level 2 reads 318 mg/dL. Which interpretation and action are correct?

2-2s across levels: systematic error; reject the run

1-2s warning only; accept and report the run

1-3s: random error; reject the run

R-4s: random error; reject the run

In an EQAS report, a laboratory's results for two samples are plotted against each other on a Youden plot. Its point lies far from the centre, along the 45° diagonal. This mainly indicates:

A transcription error on one sample

Both levels of a urea control move abruptly to about +2.5 SD on the day a new reagent lot is started and stay there, while earlier runs scattered around the mean. This pattern is:

A shift caused by systematic error

Normal variation needing no action

A trend caused by reagent deterioration

Random error from poor pipetting

Quality control and automation

29 Kerala MSc MLT Entrance practice questions on Quality control and automation, part of Biochemistry. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A laboratory's creatinine EQAS results over three cycles have SDIs of +2.4, +2.6 and +2.3, against a peer group using the same analyser and reagent (acceptable within ±2). Its internal QC, with limits set from its own data, has stayed within ±2 SD throughout. The most appropriate conclusion is:
1. APeer group mismatch; change the comparison group
2. BPoor precision; widen the internal QC limits
3. CRandom error on the EQAS samples; no action needed
4. DA constant bias that internal QC cannot detect; check calibration
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Answer: D · A constant bias that internal QC cannot detect; check calibration
The SDI is (laboratory result - peer mean) / peer SD, and three consecutive values above +2 show a consistent positive bias. Internal QC detects change from the laboratory's own established mean; if that mean was set while the bias already existed, IQC stays in control and cannot reveal it. The calibration, calibrator lot and traceability should be checked and corrected. Random error would give SDIs of varying sign and size, and the peer group already matches the method.
- A: The peer group uses the same analyser and reagent, so it is the right comparison.
- B: The problem is bias, not imprecision; wider limits would hide errors.
- C: Random error would not give three consecutive SDIs above +2 in the same direction.
Question 2 · Hard
A glucose method uses two controls: level 1 mean 100 mg/dL, SD 3 mg/dL; level 2 mean 300 mg/dL, SD 8 mg/dL. All previous runs were within ±1 SD. Today level 1 reads 107 mg/dL and level 2 reads 318 mg/dL. Which interpretation and action are correct?
1. A2-2s across levels: systematic error; reject the run
2. B1-2s warning only; accept and report the run
3. C1-3s: random error; reject the run
4. DR-4s: random error; reject the run
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Answer: A · 2-2s across levels: systematic error; reject the run
Level 1 is (107 - 100) / 3 = +2.3 SD and level 2 is (318 - 300) / 8 = +2.25 SD. Both controls in the same run exceed +2 SD on the same side, which breaks the 2-2s rule across levels. This points to a systematic error, such as calibration drift, so patient results are held and the cause corrected before rerunning. Neither control exceeds 3 SD, and the range between them is far below 4 SD.
- B: The 1-2s warning leads on to 2-2s, which is broken here, so the run cannot be accepted.
- C: Neither control exceeds 3 SD, so 1-3s is not broken.
- D: R-4s needs one control above +2 SD and the other below -2 SD.
Question 3 · Easy
Medical laboratories seeking NABL accreditation must meet the requirements of which standard?
1. AISO 9001
2. BISO 15189
3. CISO 17025
4. DISO 14001
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Answer: B · ISO 15189
The National Accreditation Board for Testing and Calibration Laboratories assesses medical laboratories against ISO 15189, which sets requirements for quality and competence specific to medical laboratories. It covers management, staff competence, equipment, pre-analytical to post-analytical processes, internal QC and participation in EQAS. NABL accreditation is increasingly required for empanelment by insurers and government schemes.
- A: ISO 9001 is a general quality management standard, not specific to medical laboratories.
- C: ISO 17025 covers general testing and calibration laboratories.
- D: ISO 14001 is the environmental management standard.
Question 4 · Medium
In an EQAS report, a laboratory's results for two samples are plotted against each other on a Youden plot. Its point lies far from the centre, along the 45° diagonal. This mainly indicates:
1. AExpected peer-group variation
2. BRandom error (imprecision)
3. CA transcription error on one sample
4. DSystematic error (bias)
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Answer: D · Systematic error (bias)
A Youden (twin) plot puts the result for sample A on one axis and sample B on the other, with the target values at the centre. A point far out along the diagonal means both results were high (or both low) by a similar amount, which is a systematic error such as a calibration bias. Points scattered away from the diagonal suggest random error or a mistake on one sample. The laboratory should check calibration and calibrator traceability.
- A: A point far from the centre is outside expected variation and needs review.
- B: Random error scatters points away from the diagonal, not along it.
- C: An error on one sample moves the point off the diagonal, parallel to one axis.
Question 5 · Medium
Both levels of a urea control move abruptly to about +2.5 SD on the day a new reagent lot is started and stay there, while earlier runs scattered around the mean. This pattern is:
1. ANormal variation needing no action
2. BA trend caused by reagent deterioration
3. CRandom error from poor pipetting
4. DA shift caused by systematic error
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Answer: D · A shift caused by systematic error
A sudden, sustained change of both control levels in the same direction is a shift, a systematic error. Its timing points to the new reagent lot, which may need recalibration or a lot-to-lot comparison. A trend is a gradual drift over many runs, as when a reagent or lamp deteriorates. Random error widens the scatter in both directions rather than moving the mean.
- A: Two levels held at +2.5 SD break the 2-2s rule and need action.
- B: A trend develops gradually over several runs, not abruptly.
- C: Random error increases scatter in both directions; it does not move both levels together.
Question 6 · Easy
What does the accuracy of a laboratory method describe?
1. AHow close results are to the true value
2. BHow close repeated results are to each other
3. CThe lowest amount the method can detect
4. DThe range over which results are linear
Answer and explanation in LearnFree account
Question 7 · Medium
Which statement correctly distinguishes a calibrator from a control?
1. ABoth set the scale but at different concentrations
2. BA calibrator sets the result scale; a control checks it
3. CBoth are patient pools with no assigned values
4. DA control sets the result scale; a calibrator checks it
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Question 8 · Medium
Replicate results of a control are very close to one another but all lie well above the target value. This method is:
1. ABoth biased and imprecise
2. BBoth accurate and precise
3. CPrecise but biased
4. DAccurate but scattered
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Question 9 · Hard
A ward patient's serum creatinine was 1.0 mg/dL yesterday and is 4.6 mg/dL today, while urea and potassium have changed markedly in a way that does not match yesterday's pattern. QC for the run is within limits and no dialysis or nephrotoxic drug is recorded. The LIS delta check flags the result. The best action is:
1. AWithhold the report and request a fresh, re-identified sample
2. BReport the result as a critical acute kidney injury
3. CRecalibrate creatinine and rerun all patients
4. DRerun the same sample and report if it agrees
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Question 10 · Medium
How is sample-to-sample carry-over on a chemistry analyser usually checked?
1. ACompare duplicate results on two analysers
2. BRun the same normal sample twenty times
3. CRun a high sample three times, then a low sample three times
4. DRun the low control after every patient sample
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Question 11 · Hard
To check carry-over, a high sample (H) and then a low sample (L) were each run three times. Results: H3 = 1,050 U/L; L1 = 70 U/L; L3 = 50 U/L. Using (L1 - L3) / (H3 - L3) x 100, the carry-over is:
1. A6.7%
2. B40%
3. C2.0%
4. D0.02%
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Question 12 · Easy
Barcode labelling of sample tubes linked to a laboratory information system mainly reduces errors in which phase of testing?
1. APre-analytical phase
2. BPost-analytical phase
3. CAnalytical phase
4. DCalibration phase
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Question 13 · Easy
Under the 2-2s rule, a run is rejected when:
1. AAny two controls in a month exceed 2 SD
2. BTwo controls differ from each other by 2 SD
3. CTwo consecutive controls exceed the same 2 SD limit
4. DTwo controls fall within 2 SD of the mean
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Question 14 · Medium
A new lot of control material is introduced. Before using its own limits on the Levey-Jennings chart, the laboratory should establish its mean and SD from:
1. ATwo runs on the first day
2. BThe mean of the previous lot
3. CThe manufacturer's stated range only
4. DAt least 20 runs on different days
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Question 15 · Medium
Dry-chemistry analysers such as Vitros use multilayer slides. The coloured product in the slide is measured by:
1. AFlame emission
2. BTransmission photometry
3. CFluorescence polarisation
4. DReflectance photometry
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Question 16 · Hard
For a creatinine method, the allowable total error is 10%, the bias against the EQAS target is 2% and the CV is 2%. Using Sigma = (TEa - bias) / CV, what is the sigma metric?
1. A5
2. B4
3. C2
4. D6
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Question 17 · Easy
The precision of a laboratory method is best expressed by its:
1. AMean of replicate results
2. BRecovery of added analyte
3. CCoefficient of variation
4. DBias from the target value
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Question 18 · Hard
A cholesterol control gave a mean of 200 mg/dL and an SD of 6 mg/dL over 20 days. What is the coefficient of variation?
1. A0.03%
2. B33.3%
3. C3.0%
4. D6.0%
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Question 19 · Medium
NABL (ISO 15189) asks laboratories to estimate the measurement uncertainty of each quantitative test. In a routine biochemistry laboratory this is mainly worked out from:
1. AThe reference range printed in the reagent kit insert
2. BThe number of samples the analyser can test in an hour
3. CThe time from sample receipt to release of the report
4. DLong-term internal QC imprecision combined with bias from EQAS or calibrator data
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Question 20 · Medium
The main purpose of an external quality assessment scheme (EQAS) is to:
1. ACompare the laboratory's accuracy with other laboratories
2. BReplace daily internal quality control runs
3. CCalibrate the analyser with assigned values
4. DDecide whether today's patient results can be released
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Question 21 · Hard
A glucose method has a bias of 3% and a CV of 2%. Using total error = |bias| + 1.65 x CV, what is the total analytical error?
1. A7.0%
2. B6.3%
3. C3.3%
4. D5.0%
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Question 22 · Medium
In Skeggs' continuous-flow AutoAnalyzer, air bubbles were introduced into the stream at regular intervals in order to:
1. ASegment samples and reduce carry-over
2. BMeasure the sample volume accurately
3. CCool the stream before the colorimeter
4. DSupply oxygen for the enzyme reactions
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Question 23 · Medium
On a Levey-Jennings chart, the glucose control rises a little each day over two weeks, from the mean to +2 SD. Which cause is most likely?
1. AOne mislabelled control vial
2. BA sudden change to a new calibrator lot
3. CGradual deterioration of the reagent or lamp
4. DAn air bubble in the sample probe
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Question 24 · Hard
In an EQAS cycle, a laboratory reports sodium as 146 mmol/L. The peer group mean is 140 mmol/L with an SD of 2 mmol/L. What is the SDI, and how is the performance judged?
1. A-3.0; unacceptable, investigate
2. B+1.5; acceptable
3. C+3.0; unacceptable, investigate
4. D+6.0; acceptable
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Question 25 · Easy
In the Westgard multirule scheme, which rule is used only as a warning that triggers checking by the other rules?
1. A2-2s
2. B1-2s
3. C1-3s
4. DR-4s
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Study Biochemistry

Quality control and automation

A laboratory's creatinine EQAS results over three cycles have SDIs of +2.4, +2.6 and +2.3, against a peer group using the same analyser and reagent (acceptable within ±2). Its internal QC, with limits set from its own data, has stayed within ±2 SD throughout. The most appropriate conclusion is:

A glucose method uses two controls: level 1 mean 100 mg/dL, SD 3 mg/dL; level 2 mean 300 mg/dL, SD 8 mg/dL. All previous runs were within ±1 SD. Today level 1 reads 107 mg/dL and level 2 reads 318 mg/dL. Which interpretation and action are correct?

Medical laboratories seeking NABL accreditation must meet the requirements of which standard?

In an EQAS report, a laboratory's results for two samples are plotted against each other on a Youden plot. Its point lies far from the centre, along the 45° diagonal. This mainly indicates:

Both levels of a urea control move abruptly to about +2.5 SD on the day a new reagent lot is started and stay there, while earlier runs scattered around the mean. This pattern is:

What does the accuracy of a laboratory method describe?

Which statement correctly distinguishes a calibrator from a control?

Replicate results of a control are very close to one another but all lie well above the target value. This method is:

How is sample-to-sample carry-over on a chemistry analyser usually checked?

To check carry-over, a high sample (H) and then a low sample (L) were each run three times. Results: H3 = 1,050 U/L; L1 = 70 U/L; L3 = 50 U/L. Using (L1 - L3) / (H3 - L3) x 100, the carry-over is:

Barcode labelling of sample tubes linked to a laboratory information system mainly reduces errors in which phase of testing?

Under the 2-2s rule, a run is rejected when:

A new lot of control material is introduced. Before using its own limits on the Levey-Jennings chart, the laboratory should establish its mean and SD from:

Dry-chemistry analysers such as Vitros use multilayer slides. The coloured product in the slide is measured by:

For a creatinine method, the allowable total error is 10%, the bias against the EQAS target is 2% and the CV is 2%. Using Sigma = (TEa - bias) / CV, what is the sigma metric?

The precision of a laboratory method is best expressed by its:

A cholesterol control gave a mean of 200 mg/dL and an SD of 6 mg/dL over 20 days. What is the coefficient of variation?

NABL (ISO 15189) asks laboratories to estimate the measurement uncertainty of each quantitative test. In a routine biochemistry laboratory this is mainly worked out from:

The main purpose of an external quality assessment scheme (EQAS) is to:

A glucose method has a bias of 3% and a CV of 2%. Using total error = |bias| + 1.65 x CV, what is the total analytical error?

In Skeggs' continuous-flow AutoAnalyzer, air bubbles were introduced into the stream at regular intervals in order to:

On a Levey-Jennings chart, the glucose control rises a little each day over two weeks, from the mean to +2 SD. Which cause is most likely?

In an EQAS cycle, a laboratory reports sodium as 146 mmol/L. The peer group mean is 140 mmol/L with an SD of 2 mmol/L. What is the SDI, and how is the performance judged?

In the Westgard multirule scheme, which rule is used only as a warning that triggers checking by the other rules?