QC % Westgard

Question 1

Mean, median, and mode

Answer 1

Mean= average

Median = the middle value in a body of media

Mode – value most frequently occurring

Question 2

Standard Deviation

Answer 2

1SD = 68%
2SD = 95%
3SD = 99.73%

Reference Range is 95% of healthy population

Question 3

Confidence Interval

Answer 3

95% Confidence interval

2SD on either side of mean

Accounts for unavoidable error caused by sampling variability and imprecision.

Question 4

%CV

Answer 4

SD X 100/Mean

Question 5

What is a more precise CV?

Answer 5

lower number

Question 6

CV Ratio

Answer 6

CVR = Lab CV/Peer Group CV

Question 7

Precision
F test

Answer 7

analysis of variance

Used to determine differences of precision between two different methods for the same analyte

Question 8

Accuracy
Paired T-test

Answer 8

Used for method correlation- looking at the means and reference intervals of two different methods for the same analyte (patient population)

Question 9

Determination of control range

Answer 9

Assay aliquot of control serum with regular batch assays for 15-25 days

Treat controls the same as specimen

Mean and SD = produce a Levey-Jennings Chart

Question 10

Sources of variance or error

Answer 10

Sampling factors
-Time of day
-Patients position
-Physical activity
-Fasting/ not fasting
-Time between draw and measurement

Procedural factors
-Aging of chemicals/reagents
-Experience of technologist
-Variations in standards, reagents, environment, methods or apparatus
-Changes in method, instruments or personnel

Question 11

Levey-Jennings Charts

Answer 11

-Evaluate unacceptable runs
-Maintain stability of analytical measurement system
-Detect changes in the system
-Plot Mean, 1 SD, 2 SD, 3 SD
-2 SD = warning
-3 SD = action needs to be taken
-Each analyte has its own chart
-When procedural changes are made they should be noted on chart
—–lot changes, new reagents, new instrument, instrument maintenance

Question 12

Shift

Answer 12

A sudden and sustained change in one direction in control sample values

Malfunction of instrument

Question 13

Trend

Answer 13

A gradual change in the control sample results

A systematic drift = control value moves progressively in one direction fro the mean for at least 3 days

Suggests a progressive problem with test system or control samples.

Example ?

Question 14

Dispersion

Answer 14

Random error or lack of precision increases

Indicate instability problems

Question 15

Westgard rules

Answer 15

System of rules that define specific performance limits for a particular assay

Can detect both systematic and random errors

Designed to improve the power of QC methods uses ± 3SD limits to detect trends or shifts

Question 16

1 2s

Answer 16

1 point is outside 2 SD = Warning

Question 17

1 3s

Answer 17

1 point is outside 3SD

Question 18

2 2S

Answer 18

two consecutive points are outside 2SD on same side of center line– Within a material and across runs.

Question 19

R 4s

Answer 19

Range of two points is greater than 4 SD–Within a material and across runs.

Question 20

4 1s

Answer 20

4 consecutive points exceed 1SD on the same side of the mean

Question 21

10x

Answer 21

10 consecutive points are above or below the mean.

Either 10 in a row within a material or 5 consecutive points across 2 runs (2 levels of control)

Question 22

Out of Control Procedures

Answer 22

Review the procedures used

Search for recent events
-New reagent
-New lot (control, reagent , calibrator)
-Environmental conditions
-Maintenance

Prepare new controls
-Typically the first method done

Calibrate the instrument

Prepare new reagents

Follow manufactures troubleshooting guide

Contact instrument manufacturer

Question 23

Calibration

Answer 23

refers to the act of evaluating and adjusting the precision and accuracy of measurement equipment. Instrument calibration is intended to eliminate or reduce bias in an instrument’s readings over a range for all continuous values.

Question 24

How to Calibrate

Answer 24

Selection of reference standards with known values to cover the range of interest.

Measure the reference standards with the instrument to be calibrated.

Plot relationship between the measured and known values of the reference standards (usually a least-squares fit to the data) called a calibration curve

Question 25

When to Calibrate

Answer 25

Before major critical measurements

After an “event”
-Maintenance
-New parts
-New instrument, reagent, control etc
-New lot

When observations or control appear questionable
-When controls are out, or when you observe a problem

Per requirement of manufacturer or procedure

*Calibration may not solve the problem.

Question 26

QC Problem: Drift (Trend)

Answer 26

Check outdates on materials

Calibrate assay

If issue is not resolved replace reagent and calibrate again.

Question 27

QC Problem: Shift

Answer 27

Look at the QC for the last 1-2 months to determine when the shift took place

What happened on that date?
-New reagent lot?
-New calibrator lot?
-Was the instrument repaired or had preventative maintenance performed around that date?

To confirm that the QC shifted calibrate a new well-mixed reagent pack with fresh calibrator.

If the shift continues= suspect an instrument malfunction, call service

Question 28

QC Problem: Random Error

Answer 28

Repeat control

If the repeat control is out of range, calibrate

If multiple assays have QC flyers suspect a QC problem (if they are run on the same control) or an instrument issue.

Question 29

QC Problem: Poor Precision

Answer 29

Replace reagent, mix well and calibrate

If problem persists, put a fresh reagent on the opposite instrument and calibrate. If time permits run QC 5X as a patient on both instruments.

Question 30

QC Problem: Shift with Poor Precision

Answer 30

Has the assay been calibrated lately? If not calibrate on a reagent pack that is at least half full, preferably a new pack.

If the QC does not improve after calibration, or the assay has been calibrated recently, compare the QC values to a second instrument if possible.

If the QC recovery is the same on both instruments, suspect a shift due to reagent lot or calibrator lot change
-If the QC recovery improves on the opposite instrument suspect an instrument issue and call to set up a service call