6. Screening

Question 1

SCREENING is applied to populations of … individuals

Answer 1

APPARENTLY WELL individuals

Illness if present is ASYMPTOMATIC

Question 2

SCREENING TESTS allow for..

Answer 2

EARLIER DETECTION and DIAGNOSIS

(assumed to lead to more effective treatment)

Question 3

2 types of SCREENING

Answer 3

MASS / POPULATION:
- applied to WHOLE POPULATION regardless of risk status

TARGETED / SELECTIVE:
- applied to HIGH-RISK groups

Question 4

when do you have DIAGNOSTIC TEST

Answer 4

If SCREENING result shows LIKELY to have disease (positive)

or SYMPTOMS

Question 5

SCREENING Vs DIAGNOSTIC test
USE

Answer 5

screening: identify people LIKELY to have pre-clinical disease

Diagnostic test: ESTABLISH ABSENCE/PRESENCE of disease

Question 6

SCREENING Vs DIAGNOSTIC test
TARGET POPULATION

Answer 6

screening: ASYMPTOMATIC or potentially AT-RISK individuals

Diagnostic Test: SYMPTOMS or POSITIVE SCREENING test

Question 7

SCREENING Vs DIAGNOSTIC test
POSITIVE RESULT..

Answer 7

screening: FURTHER INVESTIGATIONS

Diagnostic test: DIAGNOSIS or TREATMENT

Question 8

SCREENING Vs DIAGNOSTIC test
CHARACTERISTICS

Answer 8

screening:
CHEAP, SAFE, ACCEPTABLE to someone with no symptoms

Diagnostic test:
EXPENSIVE, INVASIVE but justifiable if needed to establish diagnosis

Question 9

SCREENING Vs DIAGNOSTIC test
PERFORMANCE

Answer 9

Screening:
HIGH SENSITIVITY - desirable to potential cases not missed

Diagnostic:
HIGH SPECIFICITY - important to minimise false positives as well as High SENSITIVITY

Question 10

REQUIRMENTS for effective SCREENING

Answer 10

• the DISEASE
• the TEST
• the TREATMENT
• the PROGRAMME

Question 11

REQUIRMENTS for effective SCREENING
what do you look at in the DISEASE

Answer 11

• important PUBLIC HEALTH PROBLEM
• EFFECTIVE TREATMENT exists
• has a DETECTABLE PRECLINICAL PHASE (DPCP)
• DPCP is fairly LONG and PREVALENT in target population
• TREATMENT MORE EFFECTIVE if applied at an EARLIER STAGE

eg better not to screen prostate cancer as most would never develop symptoms, detecting and treating would be more harmful

Question 12

REQUIRMENTS for effective SCREENING
what to look at in the TEST (screening and diagnostic)

Answer 12

• VALIDITY (/accurate)
  sensitivity & specificity
• RELIABLE (reproducible/precise)
• SIMPLE and CHEAP
• SAFE and ACCEPTABLE

(generally needs to be reliable to be valid)

Question 13

what is SENSITIVITY and how is it calculated

Answer 13

the proportion of all people WITH DISEASE who test POSITIVE (True positives)
(how many people who have the disease are also testing positive)

SENSITIVY = TRUE POSITIVES / ALL with DISEASE

POSITIVE IN DISEASE

Question 14

What is SPECIFICITY and how is it calculated

Answer 14

Proportion of all the people WITHOUT DISEASE who TEST NEGATIVE (true negatives)
(how many people who don’t have disease also test negative)

SPECIFICITY = TRUE NEGATIVES / ALL WITHOUT DISEASE

NEGATIVE IN HEALTH

Question 15

SENSITIVITY of a test is the ability of a test to CORRECTLY IDENTIFY those with or without target condition

Answer 15

those WITH target CONDITION

Question 16

SPECIFITY of a test is the ability of a test to CORRECTLY IDENTIFY those with or without target condition

Answer 16

those WITHOUT target CONDITION

Question 17

HIGH SENSITIVITY means

Answer 17

LOW FALSE-NEGATIVES

highly sensitive test - trust the negative test to RULE OUT the disease

Question 18

HIGH SPECIFICITY means

Answer 18

LOW FALSE POSITIVES

Highly specific test - trust the positive result to RULE IN the disease

Question 19

what is PPV (Positive Predictive Values) and how do you calculate

Answer 19

the PROPORTION of all people who TEST POSITIVE who really HAVE the DISEASE
(how many of the positive results are actually true)

PPV = TRUE POSITIVE / ALL POSITIVES

Question 20

What is NPV (Negative Predictive Values) and how do you calculate

Answer 20

PROPORTION of all people who TEST NEGATIVE who do NOT have DISEASE

(how many of the negative results are actually true)

NPV = TRUE NEGATIVES / ALL NEGATIVES

Question 21

2 RULES for SCREENING & Diagnostic TESTS

Answer 21

• CANNOT have both specificity and sensitivity
  increase in one causes decrease in the other
• PREVALENCE matters (predictive values)

Question 22

what determines PREDICTIVE VALUES

Answer 22

• the SENSITIVITY and SPECIFICITY of the test
• the PREVALENCE of the disease in population being tested
  INCREASE PREVALENCE:
  INCREASE PPV
  DECREASE NPV

Question 23

REQUIREMENTS for effective SCREENING:
how must the TREATMENT and PROGRAMME E

Answer 23

• proposed treatment EFFECTIVE and EARLY INITIATION must IMPROVE disease outcomes
• Demonstrably EFFECTIVE IN PRACTICE
• HEALTHCARE SYSTEM can COPE with flood of EXTRA diagnostic testing, treatment, follow-up
• COST-EFFECTIVE

Question 24

POTENTIAL HARMS on an INDIVIDUAL of SCREENING

Answer 24

• ANXIETY (FALSE POSITIVE results)
• Unnecessary investigations and invasive procedures
• False reassurance leading to delayed presentation (FALSE NEGATIVE results)

Question 25

POTENTIAL HARMS on a POPULATION of SCREENING

Answer 25

• WASTE of resources
• OVER-TREATMENT
  -Undermine primary prevention programmed if those who test negative feel they have ‘escaped’ disease and can continue risky behaviours

Question 26

how many UK SCREENING PROGRAMMES

Answer 26

11 (36 health conditions)

• 3 PREGNANT women
• 3 NEW-BORNs
• 5 YOUNG PEOPLE/ADULTS (3 cancers)

Question 27

UK NSC recommends introduction of..

Answer 27

TARGETED SCREENING for LUNG CANCER

high risk people

Question 28

UK SCREENING PROGRAMMES and who does what

Answer 28

1. UK NATIONAL SCREENING COMMITTEE
   makes evidence-based RECOMMENDATIONS about which conditions should be screened for
2. DEPARTMENT of HEALTH & SOCIAL CARE
   sets the POLICY, provides STRATEGY OVERSIGHT and FINANCES screening programmes
3. NHS ENGLAND
   COMMISSIONS and DELIVERS screening services
4. PUBLIC HEALTH ENGLAND
   provides EXPERT ADVICE and QUALITY ASSURES the screening programmes