Lab testing & disease screening in popln

Question 1

define pre-analytic

possible errors

Answer 1

everything done before sample is received in lab

errors: wrong test ordered, mislabelled, fasting vs not-fasting. 75% of errors

Question 2

analytic phase

Answer 2

performing test

errors: random (bubbles in system), systematic (tempterature)

Question 3

post-analytic

Answer 3

generating report, interpretation

errors: results reported under wrong patient, results interpreted incorrectly

Question 4

how are “normal ranges” determined

Answer 4

Use roughly Gaussian distribution - values within 95% of mean are normal. 5% of healthy will have abnormal results

Question 5

Define TP, TN, FP, FN

Answer 5

TP - true positive - positive test and has disease
TN - true negative - tested positive and doesnt have disease
FP - false positive = tested positive but doesn’t have disease
FN - false negative - tested negative but does have disease.

Question 6

sensitivity

Answer 6

TP / (TP+FN)
describes the probability that test will be positive in presence of disease. more sensitive = more likely patient with disease will test positive

Question 7

specificity

Answer 7

TN/(TN+FP)

describes the probability that the test will be negative in the absence of disease

Question 8

SNOUT

Answer 8

Sensitivity
Negative
OUT -
sensitive test giving negative result rules out that disease

Question 9

SPIN

Answer 9

Specificity
Positive
In
a specific test giving positive result rules in that disease

Question 10

positive predictor value

Answer 10

TP/(TP+FP)

if patient has positive test result, predict the likelihood that the patient has the disease

Question 11

negative predictor value

Answer 11

TN/ (TN+FN)

if patient has negative test result, what is probability that patient is disease free.

Question 12

screening a population for disease

Answer 12

screening is systematic application of test to ID individuals at a sufficient risk of prevalent specific disorder. they’d benefit from further investigation, preventative action.

Question 13

incidence

Answer 13

number of new cases in a fixed time period

Question 14

prevalence

Answer 14

how many ppl actually living with the disease at any point in time.

Question 15

ideal conditions for screening

Answer 15

1. benefit to patient
2. effective - target popln has significant prevalence; suitable screening test; target popln ID’d; test available to target popln.
3. inexpensive, noninvasive
4. excellent sensitivity & specificity
5. positive screening followed up with diagnostic .