Principles of Lab testing

Question 1

highest source of error

Answer 1

preanalytic- wrong tube, wrong patient

Question 2

phases of testing

Answer 2

pre analytic
analytic
post analytic

Question 3

source of error in analytic phase

Answer 3

imprecise instrument

Question 4

source of error post analytic phase

Answer 4

results don’t make sense in clinical context

Question 5

precision

Answer 5

consistent, repeatable results (cluster on target)

Question 6

measures of central tendency

Answer 6

mean

median

Question 7

measures of variability

Answer 7

standard deviation

coefficient of variation

Question 8

meaning of coefficient of variation

Answer 8

low = precise

Question 9

accuracy

Answer 9

closest to true value (near bullseye)

Question 10

sensitivity

Answer 10

probability of a positive test given a disease

a/a+c

Question 11

use of sensitivity

Answer 11

rule out a diagnosis- screening

Question 12

specificity

Answer 12

probability of negative test given no disease

d/b+d

Question 13

use of specificity

Answer 13

confirm a diagnosis

Question 14

what changes with prevalence

Answer 14

PPV and NPV

Question 15

what is constant

Answer 15

sensitivity and specificity

Question 16

which s better for individual patients

Answer 16

PPV and NPV

Question 17

prevalence

Answer 17

probability of having the disease (pretest probability)

Question 18

PPV

Answer 18

probability of disease given positive result

a/a+b

Question 19

NPV

Answer 19

probability of no disease given negative result

d/c+d

Question 20

Bayes’s therom

Answer 20

P(D+|T+) = P(T+|D+) * P(D+)/P(T+)

Question 21

truth table set up

Answer 21

top- Disease + disease -; a to b

side- test + test -; c to d

Question 22

types of bias

Answer 22

availability
representativeness
anchoring
value-induced

Question 23

availability

Answer 23

overestimation based on recent experience

Question 24

representativeness

Answer 24

overestimation of rare disease based on typical picture

Question 25

anchoring

Answer 25

failure to change theory based on new information

Question 26

value-induced

Answer 26

overestimate based on association with bad outcomes

Question 27

source of reference interval

Answer 27

95% confidence interval

Question 28

determination of cut off values

Answer 28

trade off between sensitivity and specificity- use ROC curves

Question 29

ROC curve

Answer 29

sensitivity vs 1-specificity

best with greatest AUC has greater discriminatory vale

Question 30

LR+

Answer 30

sensitivity / 1-specificity

Question 31

LR-

Answer 31

1-sensitivity / specificity