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Lab Man > Chapter 10: Quality Control > Flashcards

Chapter 10: Quality Control Flashcards

1
Q
  • Also known as “Internal Quality Control or Statistical Process Control”
  • is a process to periodically examine a measurement procedure to verify that it is performing according to pre-established specifications.
A

Quality Control

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2
Q

Clinical Laboratory Test

A
  • To evaluate the pathophysiologic condition of an individual patient
  • To assist with diagnosis
  • To guide or monitor therapy
  • To assess risk for a disease or for the progression of a disease.
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3
Q

Factors that contribute to TOTAL ERROR

A
  • Pre-analytic variability
  • Analytic variability
  • Interfering substances
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4
Q

sample collection, transportation, processing, and storage

A

Pre-analytic variability

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5
Q

test performance

A

Analytic variability

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6
Q

drugs or metabolic components

A

Interfering substances

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7
Q
  • Called “QC sample materials”
  • are measured periodically in the same manner as clinical samples, and their results are examined to determine that the measurement procedure meets performance requirements appropriate for patient care.
A

Surrogate samples

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8
Q
  • Dispersion of results

- SD is a measure of expected imprecision in a measurement procedure when it is performing correctly

A

Imprecision

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9
Q
  • is the difference between the observed mean and the expected value for a QC material.
  • If the calibration changes for any reason, a systematic bias is introduced
A

Systematic Bias

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10
Q

a method which eliminates systematic bias (within uncertainty limits)

A

-Correct calibration

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11
Q
  • Closeness of measured value to a standard or known value
A

Accuracy

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12
Q
  • Refers to the closeness of two or more measurements to each other, regardless of whether those measurements are close to the known value
A

Precision

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13
Q

Primary Purpose of Measuring QC Samples

A
  • statistically evaluate the measurement process to verify that the method continues to perform within the specifications consistent with acceptable systematic bias and imprecision
  • identify that a change in performance occurred that needs to be corrected.
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14
Q

The performance of a new method can be assessed for accuracy by _____

A

Assaying patient specimens or interlaboratory survey materials with known values

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15
Q
  • Used for individual results and is a combination of systematic bias and imprecision that occurred for that specific measurement.
A

Assaying Patient Specimens

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16
Q

used to refer to an average systematic bias that may be present in a given method

A

Trueness

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17
Q

most often performed by the laboratory using calibrator materials provided by the method or instrument manufacturer

A

Calibration

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18
Q

require calibration or calibration verification at least every 6 months, or more frequently if recommended by the method manufacturer

A

Clinical Laboratory Improvement Act (CLIA) regulations, Section 493.1255

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19
Q
  • component of a quality management system
  • part of the process management component of the quality system that integrates good laboratory practices to ensure correct patient results.
A

Statistical Quality Control

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20
Q
  • required for all aspects of laboratory operation, including statistical quality control
A

Standard Operating Procedures (SOPs)

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21
Q

If the QC result is within acceptable limits of the known value

A

the measurement procedure is verified to be stable and results for patient samples can be reported

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22
Q

If a QC result is not within acceptable limits

A

the measurement procedure is not performing correctly, results for patient samples are not reported, and corrective action is necessary

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23
Q
  • also called Shewhart plot (Shewhart, 1931)

- most common presentation for evaluating QC results

A

Levey-Jennings (Levey, 1950)

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24
Q

±1 SD

A

68.3% of observations

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25
Q

±2 SD

A

95.4% of observations

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26
Q

±3 SD

A

99.7% of observations

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27
Q

QC materials should be selected to

A

Provide analyte concentrations that monitor the analytic measurement range of the method

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28
Q

Common response of quantitative measurement procedures

A

Linear Response

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29
Q

In the case of non-linear method response, it may be necessary to

A

Use additional controls at intermediate concentrations

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30
Q

The QC materials selected must be

A

Manufactured to provide a stable product that can be used for an extended time period, preferably 1 or more years for stable analytes.

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31
Q

Use of a single lot for an extended period allows

A

reliable interpretive criteria to be established that will permit efficient identification of an assay problem, avoid false alerts due to poorly defined expected ranges for the QC results and minimize limitations in interpreting values following reagent and calibrator lot changes

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32
Q

Limitations of Quality Control Materials

A

o Non-commutable
o Deterioration of the analyte during storage
o Multi-constituent control materials caused by solubility considerations or potential interactions between different constituents, particularly at higher concentrations.

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33
Q

Several Parameter for the Frequency to Assay QC Samples

A
  • Analytic stability of the measurement procedure
  • Risk of harm to a patient from clinical action being taken before a significant error is detected
  • Number of patient results produced in a period of time when an error condition existed but was not yet detected
  • Events such as recalibration or maintenance that may alter the current performance condition of the measurement system
  • Training and competency of the test operator, particularly for manual or semi-automated methods
  • Risk of failure of the measuring device
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34
Q

The more stable the system

A

The less frequently a statistical QC evaluation needs to be performed

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35
Q

examine controls at least once per 24 hours, or more frequently if specified by the method manufacturer, or if the laboratory determines that more frequent QC assays are necessary for the performance characteristics of a method

A

CLIA regulations, section 493.1256 (Department of Health and Human Services, 2003)

36
Q 
EP23 Guidelines 
(RISK OF HARM TO A PATIENT AND NUMBER OF PATIENTS WHO MAY BE AT RISK)
A
  1. how to develop a QC plan based on evaluation of risk of harm to a patient
  2. assessment of the effectiveness of risk mitigation procedures using information from the manufacturer and from other sources
  3. combined with the clinical requirements of the local health care setting and conditions in the laboratory
37
Q

responsible for ensuring that a result has a high probability to be correct at the time it is reported for clinical use

A

Laboratory Director

38
Q
  • Introduced in the CLIA quality control requirements Survey Procedures and Interpretive Guidelines for Laboratories and Laboratory Services
  • Justify less frequent QC for measurement systems that utilized built-in control procedures to monitor various aspects of the measurement process.
A

Equivalent Quality Control (EQC)

39
Q

New option introduced by the Centers for Medicare and Medicaid Services

A

Individualized Quality Control Plan (IQCP) in 2014

40
Q

When is it necessary to do an Event-Based Quality Control Sample Assay

A

Before and After a scheduled event

41
Q
  • estimated for a QC material that represents the typical imprecision of the method when it is performing according to its design specifications
  • conventional way to express method variability and assumes the QC data can be described by a Gaussian (normal) distribution even though non-Gaussian components of variability influence the QC results
A

SD

42
Q

• When a method has been established in a laboratory, and a new lot of QC material is being introduced

A

the target value for the new lot of QC material is used along with the well-established SD from the previous lot.

43
Q

• If target values for the old and new lots are substantially different

A

a different SD may occur, and adjustment to the SD may be necessary as additional experience with the new lot is accumulated

44
Q

commonly used to assess how well a method performs relative to the medical requirement

A

Sigma metric

45
Q

compares the variability in a measurement process in standard deviations to the variability that is acceptable because it will not cause an error in diagnosis or treatment of a patient

A

Sigma scale

46
Q

the sigma metric is calculated as

A

(TEa − bias ) SD

47
Q

TEa

A

the total error

48
Q

refer to performance characteristics of the laboratory method

A

absolute value of bias and SD

49
Q

used to determine if a change in bias has occurred compared to the condition established by calibration of a method

A

QC Results

50
Q

assumes a Gaussian or normal distribution for repeated measurements

A

Sigma

51
Q

refers to a condition when the variability in the measurement process is sufficiently smaller than the medical requirement that erroneous results are very uncommon

A

six sigma

52
Q

less robust and have a higher probability that erroneous results could be produced but still at a fairly low frequency

A

four sigma

53
Q

produce enough erroneous results even though it met its performance specifications that it would not be very reliable for patient care

A

two sigma

54
Q

preferred to monitor for bias trends

A

cumulative sum (CUSUM) or exponentially weighted moving averages (EWMA)

55
Q

used to express the probability that a QC interpretive rule will detect an analytic error of a given magnitude

A

Power function graphs

56
Q

frequently used to establish acceptance criteria (rules) to evaluate QC results based on data acquired over a long enough time to adequately quantify the expected variability when a method is working correctly

A

Empirical Judgement

57
Q

does not identify random events (e.g., a temporary clot in a sample pipette, a random reagent pipette error) that do not persist until the next QC sample is measured

A

Periodic measurement of QC samples

58
Q

Determines that a method’s performance is marginal or inadequate to meet medical requirements

A

process of reviewing statistical parameters for QC data

59
Q

If the method performance cannot be improved and a better method is not available

A

the laboratory can either discontinue the test if the performance is inadequate or apply more stringent QC practices when the performance is marginal

60
Q

More stringent QC will

A

NOT improve method performance but is intended to identify smaller changes in method performance that could affect patient care decisions based on the results

61
Q

occurs when a QC result fails an evaluation rule, which indicates that an analytic problem may exist

A

QC Alert

62
Q

Repeating the QC measurement on the same QC sample is not recommended because,

A

it is more likely that a measurement system problem exists than the QC result was a statistical outlier

63
Q

When repeat testing of a new QC sample does not resolve the alert situation

A

the instrument and reagents should be inspected for component deterioration, empty reagent containers, mechanical problems, and so on

64
Q

establish acceptable criteria to determine if the repeat results agree adequately to permit reporting of original results without issuing a corrected report

A

Laboratory Director

65
Q

determine if patient results can be reported and used for clinical decision making

A

immediate impact of QC data

66
Q

QC review process two major functions

A

o It verifies that test procedures are stable and meet performance specifications
o It identifies test procedures that may need intervention to address trends in performance deterioration

67
Q

an opportunity to examine any aspect of assay performance that is relevant for a given measurement procedure to provide results that meet the requirements for clinical care decisions

A

QC review

68
Q

Why is careful reagent lot crossover evaluation of QC target values is necessary?

A

Because the matrix-related interaction between a QC material and a reagent can change with a different reagent lot, QC results may not be a reliable indicator of a method’s performance for patient samples following a reagent lot change

69
Q

• The number of patient samples to use for verifying the performance of a new reagent lot will depend on

A

the imprecision of an assay, and the concentrations at which key clinical decisions are made

70
Q

recommends a minimum of 3 patient samples and possibly more, depending on the number of key clinical decision concentrations and the imprecision of an assay

A

CLSI document EP26 (CLSI, 2013)

71
Q

The second step for the Assessment of Potential Matrix Impact on QC target values following reagent lot change
- keeps the expected variability centered around the QC target value so that QC interpretive rules will remain valid

A

evaluation of results for each QC material to determine if its target value is correct for use with the new lot of reagent

72
Q

Failure to make a target value adjustment will

A

introduce an artifactual bias in subsequent QC results, causing both an increased false alert rate and a decreased ability to detect some error conditions

73
Q

typically performed on a single day and will likely provide only a few QC results from which to evaluate if the target value has changed

A

reagent lot verification

74
Q

Failure to adjust the QC target value will

A

Cause inappropriate acceptability criteria to be used for evaluating the QC results

75
Q

When a new lot of calibrator is used, with no change in reagents

A

There is no change in matrix interaction between the QC material and the reagents

76
Q

provide a reliable indication of calibration status with the new lot of calibrator

A

QC results

77
Q

If the QC results indicate a bias following use of a new lot of calibrator

A

the calibration has changed and needs to be corrected to ensure consistent results for patient samples

78
Q

four principal ways to support the QC processes in a laboratory

A

o To verify consistency of patient results when changing lots of reagent or calibrators for a method (discussed in the previous section)
o To identify inconsistent results using a delta check with a previous result for a patient
o To verify consistency of patient results when an analyte is measured using more than one instrument or method in a health care system
o To verify method performance using results from patient samples in a statistical QC scheme

79
Q

errors that can be identified by comparing a patient’s current test result to a previous result for the same analyte
-useful to identify an interfering substance

A

delta check

80
Q

require that the relationship between test results from different methods or from multiple locations should be evaluated at least twice a year

A

• CLIA regulations, section 493.1281

81
Q

important limitation for using patient data to evaluate consistency within a single method, or between different methods for the same analyte

A

physiologic homogeneity of results

82
Q

 Aka “external quality assessment” and “interlaboratory comparison”
 Samples are passed on to different laboratories where they will be tested, then the results are compared to the reference value.
 Used to verify if the performance of a laboratory is acceptable.

A

PROFICIENCY TESTING

83
Q

It is the “property of a PT/EQA sample whereby the sample has the same numeric relationship between measurement procedures as observed for a panel of representative clinical patient samples”.

A

commutability

84
Q

Why are non-commutable PT materials subjected to peer group grading?

A

There is no reference target value because of matrix-related bias. Hence, they use the second method in comparing results which is to get the mean of all the results. Keep in mind that only laboratories that used the same method and similar technologies can be grouped together.

85
Q

refers to the overall process used to ensure that laboratory results meet the requirements for health care services to patients

A

QUALITY MANAGEMENT

86
Q

useful indicators of method performance issues

A
  • Frequency of QC alerts
  • Frequency of recalibration based on QC alerts
  • Number of reagent changes due to QC alerts
  • Number of times controls were repeated because of QC alerts
  • Frequency of unscheduled maintenance due to QC alerts
  • Number of patient samples repeated based on QC alerts
  • Frequency that patient samples are repeated based on QC alerts
  • Number of patient results corrected

Lab Man (9 decks)

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