Lecture 10: Quality Control

Question 1

Quality control vs quality assurnace

Answer 1

Quality Control - QC refers to the measures that must be included during each assay run to verify that the test is working properly.

Quality Assurance - QA is defined as the overall program that ensures that the final results reported by the laboratory are correct.

“The aim of quality control is simply to ensure that the results generated by the test are correct. However, quality assurance is concerned with much more: that the right test is carried out on the right specimen, and that the right result and right interpretation is delivered to the right person at the right time”

Question 2

Consequences of unreliable performance

Answer 2

patient misdiagnosis
delays in treatment
increased costs

Question 3

What are the 3 types of errors and when do they occur?

Answer 3

Pre-analytical:-
errors before the sample reaches the laboratory

Analytical:-
errors during the analysis of the sample

Post-analytical:-
errors occurring after the analysis

Question 4

6 forms of pre-analytical errors and example

Answer 4

1. Improper preparation of the patient
   Not fasted for glucose test

2.Improper collection of the blood sample:
sample haemolysis
LDH, potassium or inorganic phosphate

3.insufficient sample volume
unable to carry out all requested tests

4.collection timing
24 hour urine

5.Incorrect specimen container:-
serum or plasma
fluoride tubes for glucose
to inhibit glycolysis
EDTA unsuitable anti-coagulant for calcium

6.Incorrect specimen storage:-
sample left overnight at room temperature
falsely elevated K, Pi and red cell enzymes
delay in sample delivery
falsely lowered levels of unstable analytes

Question 5

Other factors on pre analytical errors

Answer 5

The sex of the patient
male or female

The age of the patient
new born / juvenile / adult / geriatric

Dietary effects
low carbohydrate / fat
high protein / fat

When the sample was taken
early morning urine collection pregnancy testing

Patient posture
urinary protein in bed-ridden patients

Effects of exercise
creatine kinase / CRP

Medical history
heart disease / diabetes / existing medication

Pregnancy
hormonal effects

Effects of drugs and alcohol
liver enzymes / dehydration

Question 6

4 Analytical errors regarding the sample

Answer 6

labelling
barcoding / aliquoting

preparation
centrifugation / aspiration

storage temperature
short –term refrigeration
medium term freezing at –20oC
long term freezing at -80oC

correct test selection
Laboratory Information Management System (LIMS)

Question 7

Analytical errors regarding glassware/pippetes/balances

Answer 7

used incorrectly
contaminated
poorly calibrated
reuse of pipette tips

Question 8

Analytical errors regarding reagents, calibrators and controls

Answer 8

poor quality

inappropriate storage
correct temperature
badly maintained fridges or freezers

stability
shelf-life / working reagent

incorrect preparation

Question 9

Analytical errors regarding the application

Answer 9

incorrect analytical procedures
poorly optimised instrument settings

Question 10

Anayltical errors regarding the instrument

Answer 10

operational limitations
temperature control/read times/mixing/carry-over

lack of maintenance
worn tubing / optics / cuvettes / probes

Question 11

5 Anayltical other factors

Answer 11

Calculation errors:
incorrect factor / wrong calibration values

Transcription errors:

Dilutions errors:
incorrect dilution or dilution factor used

Lack of training:

The human factor:
tiredness / carelessness / stress

Question 12

Post anayltical errors

Answer 12

The prompt and correct delivery of the correct report on the correct patient to the correct Doctor.

How the Clinician interprets the data to the full benefit of the patient.

Question 13

Accuracy vs percision

Answer 13

Accuracy refers to the agreement between your value and the ‘true’ value, that is how correct your result is.

Accuracy is generally measured by direct comparison to a reference value or more commonly by using assayed quality control serum, with an accurate value assigned by the manufacturer.

When analysed the closer your result obtained is to this target value, the greater your accuracy.

Precision refers to the reproducibility of your results, or the agreement between replicate measurements.

The closer your results, are to each other, for the same analyte in the same serum, the better your precision.

When evaluating a method, precision should be assessed in terms of within run performance (Intra-assay precision) and between run performance (Inter-assay precision).

Question 14

Sensitivity vs specificity and what do they affect, accuracy or percision?

Answer 14

Sensitivity: The ability to detect small quantities of a measured component.

will affect both precision and accuracy at the bottom end of the assay range.

Specificity: The ability of a method to measure solely the component of interest.


A lack of specificity will affect accuracy
falsely elevated values
hormones and drugs
falsely low values
Bromocresol purple method with bovine albumin

Question 15

SD and percision

Answer 15

the lower the SD the better the percision

Question 16

Coefficient of Variation equation and defination

Answer 16

A %CV takes into consideration the magnitude of the overall result.
The coefficient of variation (CV) is the ratio of the standard deviation to the mean. The higher the coefficient of variation, the greater the level of dispersion around the mean. Shows variability of test performance

CV = (SD/ Mean) x 100%

Question 17

How can Analytical 
Quality be Controlled ?

Answer 17

Internal Quality Control (IQC).
daily monitoring of quality control sera


External Quality Assessment (EQA).
comparing of performance to other laboratories.

Question 18

What is involved in internal quality control?

Answer 18

Daily monitoring
precision
accuracy


Quality control sera
results within control limits indicates that analytical system is running satisfactorily

Question 19

Purpose of westgard rules?

Answer 19

defines acceptability
minimises false rejections
maintains high error detection
detect random and systemic errors

Question 20

how many mandatory and warning rules are there AND what happens when a mandatory and warning rule is broken?

Answer 20

3 are warning rules and the other 3 mandatory rules.

The violation of warning rules should trigger a review of test procedures, reagent performance and equipment calibration.

The violation of mandatory rules should result in the rejection of the results obtained with patients’ serum samples in that assay.

Question 21

Describe the warning rules

Answer 21

Warning 12SD : It is violated if the IQC value exceeds the mean by ±2SD. It is an event likely to occur normally in less than 5% of cases.

Warning 22SD : It detects systematic errors and is violated when two consecutive IQC values exceed the mean on the same side of the mean by ±2SD.

Warning 41SD : It is violated if four consecutive IQC values exceed the same limit (mean ± 1SD) and this may indicate the need to perform instrument maintenance or reagent calibration.

Question 22

Describe the mandatory rules

Answer 22

Mandatory 13SD : It is violated when the IQC value exceeds the mean by ±3SD. The assay run is regarded as out of control.

Mandatory R4SD : It is only applied when the IQC is tested in duplicate. This rule is violated when the difference in SD between the duplicates exceeds 4SD.

Mandatory 10x : This rule is violated when the last 10 consecutive IQC values are on the same side of the mean or target value.

Question 23

QA vs QC (4 additional aspects)

Answer 23

QA:
Prevent Defect
Proactive process
Process based approach
Manage quality

QC:
Identify defect
Reactive process
Product based approach
Verify quality

Question 24

What does each westgard rule affect - cause inaccuracy or imprecision?

Answer 24

12s - inaccuracy/impercision
22S - impercision
41S - inaccuracy

13S - inaccuracy/impercision
R4S - impercision
10X - inaccuracy

Question 25

Poor Accuracy causes…
Poor Precision causes

Answer 25

Poor Accuracy causes systemic errors
Poor Precision causes Random errors

Question 26

IQC vs EQA

Benefits of EQA?

Answer 26

Internal quality control monitors the daily precision and accuracy of methodologies, personnel, and instruments.
External quality control maintains long term accuracy.

Some key benefits of participation in a proficiency program include:
- Demonstration of technical competence
- Identification of potential areas for improvement
- Increased confidence in the accuracy of the laboratory’s testing results
- Verification of the effectiveness of training

Question 27

Parts of IQC and EQA

Answer 27

Internal Quality Control (IQC)
Intra-lab Comparisons
Intra-lab Precision
Daily Evaluation

External QA
External Quality Assurance Programs (EQAP)
Proficiency Testing
Inter-lab Patient Swaps/Exchanges/Comparisons
Long Term Evaluation

Question 28

How often do u run QC

Answer 28

• Within-run (intra-batch)
• Between-run or within-day
• Day-to-day (inter-batch) (BEST OPTION)

Quality Control materials shall be periodically examined with a frequency that is based on the stability of the procedure and the risk of harm to the patient from an erroneous result.”

Question 29

aspects of Pre, ana, post anayltical testing

Answer 29

Pre-analytical: test request, patient and specimen identification, specimen collection, transport, accessioning and processing

Analytical: specimen testing

Post-analytical: reporting test results, interpretation, follow up, storage, retesting if needed.