L79 - Diagnostic and Screening Tets

Question 1

Sensitivity

Answer 1

Percentage of people with disease that test positive

TP/(TP + FN)

Question 2

Specificity

Answer 2

Percentage of people without disease that test negative

TN(TN + FP)

Question 3

Positive Predictive Value

Answer 3

Number of positive tests that are truly positive

TP/(TP + FP)

Question 4

Negative Predictive Value

Answer 4

Number of Negative Tests that are Truly Negative

TN/(TN + FN)

Question 5

Likelihood Ratio

Answer 5

Likelihood that a given test result would be expected in a patient with the disease compared to a patient without the disease

Question 6

LR of positive test

Answer 6

sensitivity / (1 - specificity)

Question 7

LR of Negative Test

Answer 7

(1 - sensitivity) / specificity

Question 8

Reciever Operator Curve

Answer 8

Indicates how well a test discriminates people with disease from people without the disease

Question 9

Screening Criteria

Answer 9

Important Health problem
Natural History Well Understood
Detectable at an early stage
early treatment is beneficial
Suitable test for early disease
Acceptable test
Intervals for testing determined
Adequate healthcare provision for extra workload
Risks (incuding psychological) are less than benefits
Costs balanced against Benefits

Question 10

Limitations of Screening

Answer 10

Inaccuracy of screening test
May not be cost-effective
Physical and Psycholofical Side-effects
Biases in measurement of effectiveness

Question 11

Selection Bias

Answer 11

Healthy more liekly to be screened

Question 12

Lead Time Bias

Answer 12

Early detection, not prolonged survival

Question 13

Length-time Bias

Answer 13

Detection of non-aggressive disease

Question 14

Overdiagnosis Bias

Answer 14

May occur if a screen program detects cases of cancer that would not lead to death in that individual’s lifetime and owuld nto have been detected with screening

• indolent cancers
• competing mortality

Can result in apparent improvement in a stage distribution, resection rates and survival without an improvement in disease specific mortality

Question 15

Population Based Screening

Answer 15

Test is offered systematcally to all individuals in a defined target group

Screening within a framework

• agreed policy
• Recruitment strategy
• protocols for screening and assessment
• quality improvement
• monitoring and evaluation

Question 16

Opportunisitc (Case Findign) Screening

Answer 16

A test is offered to an asymptomatic individual when they present to a health care practitioner for unrelated reasons:

Limitation:

• May not be appropriate target group
• variation sin assessment and treatment
• lack of quality assurance and outcome assessment