Lecture 12 10/17/24

Question 1

What is analytical performance?

Answer 1

how well the test measures

Question 2

What is diagnostic performance?

Answer 2

how well the test detects disease

Question 3

What is pre-analytical error?

Answer 3

things that go wrong before analyte measurement

Question 4

What are the problems that fall into pre-analytical error?

Answer 4

-patient preparation
-sample acquisition
-sample handling
-sample storage

Question 5

What is analytical error?

Answer 5

things that go wrong during analyte measurement

Question 6

What are the problems that fall into analytical error?

Answer 6

-instrument
-reagents
-instrument operator

Question 7

What is post-analytical error?

Answer 7

things that go wrong after analyte measurement

Question 8

What are the problems that fall into post-analytical error?

Answer 8

-data reporting
-data interpretation

Question 9

What is random error/imprecision?

Answer 9

-variation of results during repeated measurement
-represented mathematically by coefficient of variation of repeatability data

Question 10

What can be reflected by imprecision?

Answer 10

unpredictable events that cause random measurement errors

Question 11

How is “true” analyte concentration determined at the manufacturing level?

Answer 11

series of measurements and calibrations is done with a reference measurement procedure and reference material representing “true” conc.

Question 12

How is “true” analyte concentration determined at the clinic level?

Answer 12

referral lab results are often a proxy for “the truth” relative to in-clinic equipment

Question 13

What is systematic error?

Answer 13

-difference between a measured result and some representation of “true” concentration/activity
-typically predictable

Question 14

What is constant bias?

Answer 14

measured value is consistently above or below the “true” value throughout the range of measured conc/activity

Question 15

What is proportional bias?

Answer 15

difference between the measured value and “true” value varies with analyte conc/activity

Question 16

What is important to note about constant and proportional bias?

Answer 16

they are not mutually exclusive and can occur together

Question 17

What are two examples of every day bias?

Answer 17

-malfunction that causes measurement error in a predictable, systematic way (problem to correct)
-two instruments are used to measure the same analyte in the same sample and give slightly different results (normal)

Question 18

How does correlation differ from agreement?

Answer 18

correlation indicates an association and trending in the same direction, but not necessary giving the same result

Question 19

How can bias between two instruments be eliminated?

Answer 19

-use instrument-specific reference intervals and medical decision thresholds to interpret data
-use the same instrument to follow trends over time

Question 20

What is assayed quality control material?

Answer 20

substance of known concentration that is measured during quality control

Question 21

Why do we run controls?

Answer 21

to document that the machine is measuring correctly and without analytical error

Question 22

What is control data?

Answer 22

results of measuring quality control material

Question 23

What are control limits?

Answer 23

numerical thresholds for deciding whether control data are acceptable or not

Question 24

What is calibration?

Answer 24

adjusting how an instrument measures according to the assigned concentration of a calibrator solution

Question 25

What are the characteristics of instrument flags?

Answer 25

-symbols printed with data -give warnings or indicate problems -should not be ignored -can be resolved using instrument manual

Question 26

What are practical tips for quality control?

Answer 26

-interpret control data at time of measurement -archive control data and review over time -do daily QC on CBC instruments; follow manufacturer instructions for CHEM instruments -re-run controls before running patient samples when problems occur

Question 27

How can pre-analytical error be prevented?

Answer 27

-proper patient preparation -proper sample acquisition -proper sample labeling, handling, storage, and transport

Question 28

How can analytical error be prevented?

Answer 28

-follow manufacturer instructions -perform QC and review control data -do not use expired materials -do not ignore instrument warning flags

Question 29

How can post-analytical error be prevented?

Answer 29

-use appropriate reference intervals -check data transfer to medical record

Question 30

What are interferents?

Answer 30

-substances that cause analytical error due to interference in the test system -pre-analytical factors that cause analytical error

Question 31

How can hemolysis be caused by patient or sample prep. error?

Answer 31

-rough venipuncture -poor sample handling

Question 32

How can hemolysis be caused by patient disease?

Answer 32

intravascular hemolytic anemia

Question 33

How can lipemia be caused by patient or sample prep. error?

Answer 33

did not fast patient

Question 34

How can lipemia be caused by patient disease?

Answer 34

-endocrine disease -idiopathic hyperlipidemia -pancreatitis

Question 35

How can icterus be caused by patient disease?

Answer 35

-hemolytic anemia -cholestatic liver disease

Question 36

What are the characteristics of population-based reference intervals?

Answer 36

-how we decide if results are "normal" or "abnormal" -reflect analyte conc. in a clinically healthy adult pop.

Question 37

What are the lower and upper reference limits?

Answer 37

statistical estimates calculated from all reference sample data that become more accurate with larger reference group size

Question 38

What are tips for using reference intervals?

Answer 38

-reference intervals are method-specific -RIs in textbooks may not apply to your chosen method -patient values can be within the RI and a pathologic state can still be present -some animals will have values outside of the RI but still be healthy -values should be interpreted in addition to patient physical exam

Question 39

What are the characteristics of medical decision limits?

Answer 39

-based on expert consensus -help us decide whether a disease is present -help stratify patients for disease classification, monitoring, and treatment

Question 40

What are the steps of implementing a new lab test?

Answer 40

-characterize analytical performance -implement QA/QC procedures to monitor analytical performance -develop reference intervals or decision thresholds -characterize diagnostic performance

Question 41

What are the metrics used to evaluate diagnostic test performance?

Answer 41

-sensitivity -specificity -positive predictive value -negative predictive value