Using Laboratory Data

Question 1

Reasons to order lab test

Answer 1

Diagnosis:confirm, screen, rule-out
Management: monitor, follow course, prognosis
Fear: criticism, insecurity

Question 2

Most common reasons for ordering a lab test?

Answer 2

diagnosis, screening, monitoring

Question 3

Lab test most likely to change the diagnosis and direct therapy?

Answer 3

microbiology reports

Question 4

Reference ranges are based on

Answer 4

range of values determined by large numbers of normal, healthy individuals (may be age, sex, race specific)

Question 5

Reference range is calculated by

Answer 5

mean value and the standard deviation

Question 6

Reference range is a ____________ curve

Answer 6

bell-shaped, Gaussian ST of +/-2 to include 95%

Question 7

Total bilirubin reference range curve

Answer 7

Non-Gaussian

Question 8

Total serum cholesterol reference range

Answer 8

is a “healthy” rand based on epidemiological studies

Question 9

Serum creatinine is a good example of

Answer 9

the necessity of comparing current value to previously determined value

Question 10

Endocrinology tests reference ranges are based on

Answer 10

stimulatory and inhibitory recordings

Question 11

In disease prognosis/progression it is important to

Answer 11

monitor change sin value (not reference range) i.e.. LDL, PSA

Question 12

What is the chance of an abnormal result if you do 1 test?
2 ind tests?
5 ind tests?
10 ind tests?

Answer 12

5%
10%
23%
40%

Question 13

Action levels

Answer 13

abnormal result that ay or may not require treatment, cholesterol > 200, LDL > 160, HDL < 35 –> patient should be more active

Question 14

Sensitivity

Answer 14

probability that a patient with a disease will test positive

Question 15

Sensitivity equation

Answer 15

Sn = 100X TP/ (TP + FN)

Question 16

Specificity

Answer 16

probability that a non-diseased patient will test negative

Question 17

Specificity equation

Answer 17

Sp = 100X TN / (TN + FP)

Question 18

Prevalence

Answer 18

pre-test probability of disease in the population

Question 19

Altering the sensitivity will

Answer 19

alter the specificity of a test and vice versa

Question 20

Choose a test with HIGH Sensitivity when

Answer 20

the probable disease is serious and curable

Question 21

Want a very sensitive test when the

Answer 21

benefit of detecting the disease are great

Question 22

Choose a test with a HIGH specificity when

Answer 22

the probable disease is serious but not treatable

Question 23

Want a highly specific test when the

Answer 23

risks of wrong diagnosis is great

Question 24

Confirmatory test

Answer 24

highly sensitive

Question 25

Common order of testing

Answer 25

sensitive tests followed by specific

Question 26

PPV

Answer 26

probability that a positive test result indicates disease

Question 27

PPV equation

Answer 27

PPV= 100X TP/ (TP + FP)

Question 28

NPV

Answer 28

probability that a negative test result indicates no disease

Question 29

NPV equation

Answer 29

NPV= 100X TN/ (TN + FN)

Question 30

Does prevalence effect the predictive value?

Answer 30

Yes, the less prevalent a disease the lower the PPV. Higher prevalence = higher PPV

Question 31

Does sensitivity and specificity effect predictive value?

Answer 31

Yes, the more sensitive/specific, the higher the PPV.

Question 32

Serial testing effect on sensitivity

Answer 32

decreases

Question 33

Serial testing effect on specificity

Answer 33

increases

Question 34

Parallel testing effect on sensitivity? specificity?

Answer 34

higher sensitivity, lower specificity

Question 35

What test would you use for a mild treatable disease?

Answer 35

good sensitivity and specificity

Question 36

Order of testing for clinicians

Answer 36

high sensitivity test followed high by specificity test

Question 37

Once prevalence reaches >50% what effect does it have on predictive value

Answer 37

not much increase in predictive value

Question 38

Is predictive value effected by cut-off values

Answer 38

Yes, cut off values change the sensitivity and specificity of a test and therefore change the PPV and NPV

Question 39

Pre-analytic errors

Answer 39

medication interference, wrong patient prep, inadequate amt of specimen, wrong specimen, delayed transport, wrong storage

Question 40

Pre-analytic variation

Answer 40

age, gender, mass, prep of patient, posture of patient, specimen type

Question 41

Analytic errors

Answer 41

wrong usage of equipment, expired reagents

Question 42

Analytic variables

Answer 42

analytical sensitivity, analytical specificity, analytical interference, precision, accuracy, drug impact, lab instruments

Question 43

Analytical sensitivity

Answer 43

ability to detect a substance; least concentration measurable by the test (high... PCR)

Question 44

Analytical specificity

Answer 44

ability to detect only 1 substance;

Question 45

Precision

Answer 45

reproducible

Question 46

accuracy

Answer 46

closeness to a known accepted value

Question 47

Post-analytical errors

Answer 47

wrong results, time delays

Question 48

Physician Factors influencing decision to order tests

Answer 48

faulty decision-making, over reliance, lack of understanding, lack of appreciation of testing limitations, etc

Question 49

Laboratory Factors influencing decision to order tests

Answer 49

convenience of automation, rapid, new tests without proven results, etc

Question 50

Medical Science factors influencing lab tests

Answer 50

new treatments that require monitoring

Question 51

Patient and Societal factors influencing lab tests

Answer 51

expectations, health ins, etc

Question 52

Hospital factors influencing lab tests

Answer 52

encouragement, ICU and dialysis centers, decreased length of stay, more severely ill patients