Lecture 6: Quality Assessment and Quality Control

Question 1

Describe what quality is

Answer 1

• Quality= degree of excellence of something
• Quality: “key measurable characteristics of a product or process whose performance standards or specification limits must be met to satisfy the customer

Question 2

Describe what quality assessment and quality control means in a lab

Answer 2

• Assessment of quality of results for analyses

- Important in operation of a high-quality lab

Question 3

Compare quality assessment and quality control

Answer 3

Quality assessment:

• management systems to guarantee integrity of data
• everybody’s business
• goal=value addition
• management strategy

Quality control:

• measurement used to check quality of analytical data
• restricted to a specific area and performed by authorised staff
• goal= error prevention
• error detected ethology

Question 4

Define the 2 types of error and describe how they can occur

Answer 4

 Active error: Occurs at the interface between a health care worker and the patient
 Latent error: Are related to the organisation or design of a laboratory
Active errors:
- failing to identify patient before phlebotomy
- missing blood vessel during phlebotomy
- errors with collection tubes
- errors with transportation system
- errors with data entry

Latent errors:

• staffing problems-> chronic shortages
• no interface w/ technology
• equipment malfunction-> old error-prone analysers
• work environment-> multitasking, poor lab layout
• policy and procedures-> relabelling tubes
• teamwork factors -> poor communication
• management/ organisation -> hen profit is goal

Question 5

What are the ways to improve overall errors

Answer 5

Training on the safety of the patient

2. Enhanced communication
3. Quality improvement projects
   - >Involving patient outcomes data and feedback of the data to lab staff, with an analysis of the consequences of high-quality and low-quality work

Question 6

What are the cost of these errors?

Answer 6

• These errors:
  1. Cost to patient
  2. Cost to hospitals

Question 7

State why Quality assessment programmes are essential

Answer 7

-> reduces and eliminates lab errors

Question 8

State the 2 components of quality assessment

Answer 8

• Non-analytical factors

- Analytical factors

Question 9

List the non-analytic factors for quality control

Answer 9

1. Qualified personnel
2. Established Lab Policies
3. Lab Procedure Manual
4. Test demand
5. Patient identification, Specimen Procurement and Labelling
6. Specimen Transportation and Processing
7. Replicate analyses using control specimens
8. Preventive Maintenance of Equipment

Question 10

Explain the analytic factors for quality control

Answer 10

• pre-analytical-> specimen collection, specimen transport, specimen quality
• analytic-> result accuracy, clerical errors, assay repeat rates
• post-analytic-> result reporting, record keeping for patient +QC

Question 11

List the errors that can occur during each stage of analysis

Answer 11

Pre-analytical errors:
- Specimen obtained from wrong
patient
- Specimen procured at the wrong
time
- Specimen collected in the wrong
tube or container
- Blood specimens collected in the
wrong order
- Incorrect labelling of specimen
- Improper processing of
specimen

Analytical errors:
- Oversight of instrument
flags
- Out-of-control quality
control results
- Wrong assay performed

Post-analytical errors:
- Verbal reporting of results
- Confusion about reference
ranges

Question 12

Define precision + accuracy

Answer 12

• Accuracy: closeness of a measured value to the true value

- Precision: ‘spread’ or variability of repeated measures of the same value

Question 13

Describe the importance of accuracy and precision

Answer 13

• Inaccurate and imprecise measurements= errors

Question 14

Define sensitivity and specificity, as well as positive and negative predictive values

Answer 14

• Sensitivity: proportion of patients with a positive test result among all the patients with the disease
• Specificity: proportion of patients with a negative test result among all the patients without the disease
• Positive predictive value (PPV): proportion of patients with the disease among all the patients with a positive test result
• Negative predictive value (NPV): proportion of patients without the disease among all the patients with a negative test result

Question 15

Give the equations for calculating sensitivity and specificity, as well as positive and negative predictive values

Answer 15

Sensitivity= TP/ TP+FN
Specificity= TN/TN +FP
PPV= TP/
TP+ FP 
NPV= TN/ TN+FN

Question 16

Define quality control

Answer 16

• Quality control: Procedures to monitor the accuracy and precision of analysis performance over time

Question 17

What activities are included in QC

Answer 17

• Quality control (QC) activities include:
• Monitoring the performance of lab instruments, reagents, other testing products and equipment
• A written record of QC activities for each procedure or function with deviation from the usual results
• How to detect the source of error? →Use of control specimens

Question 18

Describe the requirements from the control specimens and what it shows

Answer 18

• Control specimens:
  1. Sample with a known concentration of the analyte
  2. Must be treated in exactly the same way as the test specimen
  3. Overall reliability (both accuracy and precision) of the results

Question 19

Define mean, median + mode

Answer 19

• Mean: mathematical average
• Median: Middle value of a list
• Mode: Value most frequently occurring in a list

Question 20

What is the Guassian distribution and what is it used for

Answer 20

• The distribution of subsequent control runs approaches a Gaussian distribution (normal distribution curve)
• Can use the standard deviation to set control ranges to our measurements

Question 21

What are Levey-Jennings Charts

Answer 21

• Plot of the daily control specimen values on a quality control chart

Question 22

Define shift and trend and state their causes

Answer 22

• Shift: Sudden and sustained change in one direction
• > Causes: Sudden malfunction of an instrument
• Trend (drift): Gradual change
• > Causes: Progressive problem with the testing system or control sample

Question 23

List the sources of variation of the control sample

Answer 23

1. Sampling factors:
   a) Time of the day when the sample is obtained
   b) Patient’s position (lying down or seated)
   c) Patient’s state of physical activity (in bed, ambulatory or physically active)
   d) Interval since last eating (fasting or not)
   e) Time interval and storage conditions between collections
2. Procedural factors:
   a) Aging of chemicals or reagents
   b) Personal bias or limited experience of the person performing the test
   c) Lab bias

Question 24

What are the Westgard rules

Answer 24

• Westgard rules used to determine if certain results should be excluded or not

Question 25

What does violation of warning rules and violation of mandatory rules mean

Answer 25

- The violation of warning rules ->trigger a review of test procedures, reagent performance and equipment calibration - The violation of mandatory rules -> rejection of the results obtained with patients’ serum samples in that assay

Question 26

Recall the Westgard rules

Answer 26

- 13s rule: A run is rejected when a single control measurement exceeds the mean ± 3SD - 12s rule: Warning rule. Triggers careful inspection of the following measurements - 22s rule: Reject when two consecutive control measurements exceed mean ± 2 SD - R4s rule: Reject when a control measurement exceeds the mean + 2 SD and another exceeds the mean – 2 SD - 41s rule: Reject when four consecutive control measurements exceed the mean ± 1SD - 10x rule: Reject when ten consecutive control measurements fall on one side of the mean, regardless of the SD.

Question 27

How can we follow up from a violation of a Westgard rule

Answer 27

- Accept the test run in its entirety - this usually applies when only a warning rule is violated - Reject the whole test run - this applies only when a mandatory rule is violated - Enlarge the grey-zone and thus re-test range for that particular assay run - this option can be considered in the event of a violation of either a warning or mandatory rule.