Analytical Performance

Question 1

What does analytical mean?

Answer 1

Assess how well an instrument/method measures an analyte of interest.

Question 2

What does diagnostic mean?

Answer 2

This is how well a given test discriminates between an individual that has a disease and a person that does not (follows analytical)

Question 3

How can analytical and diagnostic performance be assessed?

Answer 3

PASS

Question 4

Why is monitoring analytical performance important?

Answer 4

• quality control
• stability of performance of lab tests
• for reg bodies
• validation of methods/assays and instruments
• calibration
• comparison between labs and different instruments.

Question 5

What is precision? two Rs

Answer 5

Repeatability and reproducibility.

Question 6

What are the 3 ways in which precision can be evaluated?

Answer 6

Intra assay (during), inter assay (between) and precision profile.
Multiple runs needed.

Question 7

How can precision be numerically defined?

Answer 7

SD(dispersion) and CV

Question 8

What does SD mean?

Answer 8

This is defined by the variation or the dispersion from the mean or expected value.

Question 9

What are the SD bell curve graph %s?

Answer 9

68.3% - 1SD
95% - 2SD
99.7% - 3SD

Question 10

What is more precise 1SD or 3SD?

Answer 10

1 SD - less of a degree of variability between measurements

Question 11

What is the average adult blood glucose level?

Answer 11

5.5 +/- 2.2 mmol/Lt

Question 12

How is SD used in clinical measurements?

Answer 12

• reference ranges for test analytes.
• assessment of analytical and diagnostic performance.
  = depends on the clinical significance of the results generated.

Question 13

How is CV calculated?

Answer 13

%Cv = (SD/mean) x100/1

Question 14

What does CV do?

Answer 14

It scales the SD by the size of the mean.

Makes it possible to compare across variables measured on different scales and allows for comparison of variability

Question 15

What is a with in run precision (intra assay)?

Answer 15

Closeness of agreement between results of successive measurements collected under identical conditions.

Question 16

What is a between run precision assay?

Answer 16

QC material representing low, med, high conc values are assayed in groups of 20 in different analytical runs over DIFFERENT DAYS

Question 17

What does a precision profile involve?

Answer 17

The examination of the variation of a method over a number of analyte concentrations, days and optionally over one or two runs per day.

Question 18

What is the plot of precision profile?

Answer 18

%Cv vs conc

Question 19

What can precision profiles be used to establish ?

Answer 19

Working reference ranges.

Ensures that imprecision is below a pre-established level.

Question 20

What are the 2 requirements needed in order to construct a precision profile?

Answer 20

• 3 replicates must be observed for each run, and each run must have the same number of replicates.
• Known conc of analyte

Question 21

What is Accuracy?

Answer 21

This is the nearness of a result to the true value.

Found measuring the % inaccuracy.

Question 22

How can % inaccuracy calculated?

Answer 22

(Nominal value - experimental value)/ nominal value x100

Question 23

What does matrix spiking, recovery study consist of?

Answer 23

Tests the ability of an assay to recover - measure a known amount of analyte from a sample matrix.

Question 24

How is the concentration recovered calculated?

Answer 24

[c] = A - B

Question 25

What is the general acceptable recovery ?

Answer 25

> 90%

Question 26

What does accuracy depend on ?

Answer 26

Specificity.

Question 27

What does specificity measure?

Answer 27

Proportion of negatives which are correctly identified (true neg)
The proportion of patients who do not have the disease who will test negative for the mutation.

Question 28

The lower the specificity the higher the ?

Answer 28

Chance of a false positive.

Question 29

How is specificity calculated?

Answer 29

true neg/ true neg + false pos. NEED to BE HIGH

Question 30

What is sensitivity ?

Answer 30

This is the ability to identify a positive results correctly.

Question 31

The higher the sensitivity the lower the ?

Answer 31

Chance of a false negative.

Question 32

What is the Limit of Detection Limit?

Answer 32

This is the the lowest quantity of a substance that can be distinguished from the absence of that substance with a degree of confidence.

Question 33

What can a sensitive assay do?

Answer 33

Measure low levels of analyte.

Question 34

How can sensitivity be calculated?

Answer 34

Opp of specificity - true pos used.

Question 35

What are the 3 situations in which clinical labs need to compare methods?

Answer 35

1. Purchase of a new analyser
2. New method introduced.
3. A quicker, more convenient or more economical adaptation to an existing interpretation.

Question 36

What are the 2 kinds of data that can be used to compare methods ?

Answer 36

• independent data about PASS

- measurements that are made by both methods on the same clinical samples.

Question 37

What are the 3 factors required for comparing methods?

Answer 37

• sufficient time for familiarisation
• samples cover the clinically encountered range of results
• sufficient number of samples analysed

Question 38

How are statistical tests applied?

Answer 38

To describe the relation between results by two methods: paired T tests, least square linear regression, Pearson correlation.