Quality Control for Quantitative Tests

Question 1

measure the quantity of a particular substance in a sample

Answer 1

Quantitative Tests

Question 2

quality control for quantitative tests is designed to assure that patient results are

Answer 2

 accurate
 reliable

Question 3

material that contains the substance being analyzed

Answer 3

Control

Question 4

used to validate reliability of the test system

Answer 4

Control

Question 5

A substance with a specific concentration

Answer 5

Calibrators

Question 6

A substance similar to patients’ samples that has an established concentration.

Answer 6

Controls

Question 7

A calibrator can become a control

Answer 7

False

Question 8

Used in laboratory conditions

Answer 8

Controls

Question 9

Characteristics of Control Materials

Answer 9

◼ appropriate for the diagnostic sample
◼ values cover medical decision points
◼ similar to test sample (matrix)
◼ available in large quantity; ideally enough for one year
◼ can store in small aliquots

Question 10

Types of Control Materials

Answer 10

◼ may be frozen, freeze-dried, or chemically preserved
◼ requires very accurate reconstitution if this step is necessary

Question 11

Sources of Controls Materials

Answer 11

◼ commercially prepared
◼ made “in house”
◼ obtained from another laboratory, usually central or reference laboratory

Question 12

Target value predetermined
Verify and use

Answer 12

Assayed Materials

Question 13

Target value not predetermined
Full assay required before using

Answer 13

Unassayed Materials

Question 14

In-house pooled sera
Full assay, validation

Answer 14

In-house Materials

Question 15

Choosing Control Materials

Answer 15

◼ values cover medical decision points
◼ similar to the test sample
◼ controls are usually available in high, normal, and low ranges

Question 16

Preparation and Storage of Control Material

Answer 16

◼ adhere to manufacturer’s
instructions
◼ keep adequate amount
of same lot number
◼ store correctly

Question 17

Steps in Implementing Quantitative QC

Answer 17

◼ obtain control material
◼ run each control 20
times over 30 days
◼ calculate mean and +/-
1,2,3 Standard Deviations

Question 18

Normal occurrence when a control is tested repeatedly

Answer 18

Variability

Question 19

Variability is affected by:

Answer 19

Operator technique (Medtech)
Environmental conditions (Environment)
Performance characteristics of the measurement (Machine)

Question 20

Measures of Central Tendency

Answer 20

Mean, Median, Mode

Question 21

the value which occurs with the greatest frequency

Answer 21

Mode

Question 22

the value at the center or midpoint of the observations

Answer 22

Median

Question 23

the calculated average of the values

Answer 23

Mean

Question 24

Not all central values are the same

Answer 24

True

Question 25

characteristic “bell-shaped” curve

Answer 25

Normal Distribution

Question 26

used to monitor the accuracy and the precision of the assay.

Answer 26

Quality Control

Question 27

The closeness of measurements to the true value

Answer 27

Accuracy

Question 28

The amount of variation in the measurements

Answer 28

Precision

Question 29

The difference between the expectation of a test result and an accepted reference value

Answer 29

Bias

Question 30

Accurate is always precise

Answer 30

True

Question 31

Precise is not always Accurate

Answer 31

True

Question 32

For a set of data with a normal distribution, a random measurement will fall within:

Answer 32

+ 1 SD 68.3% of the time + 2 SD 95.5% of the time + 3 SD 99.7% of the time

Question 33

principle measure of variability used in the laboratory

Answer 33

Standard Deviation

Question 34

SD expressed as a percentage of the mean.

Answer 34

Coefficient of variation

Question 35

Graphically Representing Control Ranges

Answer 35

Levey-Jennings Chart

Question 36

results with no pattern-only a cause for rejection if outside 2SDs

Answer 36

random error

Question 37

not acceptable, correct the source of error

Answer 37

systematic error

Question 38

control on one side of the mean 6 consecutive days

Answer 38

shift

Question 39

control moving in one direction–heading toward an “out of control” value

Answer 39

trend

Question 40

represents a range of values in which the true value is reasonably expected to lie

Answer 40

Measurement Uncertainty

Question 41

Measurement Uncertainty is estimated at

Answer 41

95% coverage

Question 42

If QC is out of control

Answer 42

STOP testing Do not report patient results until problem is solved