WEEK12: Screening and secondary prevention Flashcards
What is prevention?
- modifying or removing risk factors that are causally related to the disease
What is primary prevention?
- aims to remove cause of the disease
Give examples of primary prevention?
- stopping smoking
- increase host resistance e.g. vaccination, nutrition= to avoid infections
- safe sex
- safe water (chlorination)
- remove lead in paint
What is secondary prevention?
- Screening for early stage disease
What is tertiary prevention?
- Treatment of established / late disease
What outcome on the disease does primary prevention have?
- less incidence
(bc removing cause of the disease)
What outcome on the disease does secondary prevention have?
- early intervention
- can treat
- better management strategy
- improve prognosis
What outcome on the disease does tertiary prevention have?
- managing and controling consequences of the disease
What is the iceberg of disease?
- Everything above the water level is what is known about the health services
- everything below the water level is not known
- people below water line= have disease but don’t know it yet
- ocean around the iceberg= people who are disease free
- tip of the iceberg (At the top of water)= tertiarty care= in hospitals
- when you screening, you are trying to identify the people beneath the iceberg who have not pick up disease yet (primary and secondary prevention)
What is secondary prevention?
- SCREENING:
- get eligible population (ASYMPTOMATIC PERSON)
= certain tests for different groups e.g. antenatal for preggo women - perform test- NOT diagnostic
- it tried to identify people at high risk
- high risk people may need further investigation
Lets say we are testing for cancer. What happens if someone screens negative?
- screen negative= means NO CANCER POSSIBILITY
- wait for next screening
- no action till next screening
- there will be some people in the group that were missed and that will develop cancer= FALSE NEGATIVE
- Some dont end up with cancer= TRUE NEGATIVE
What happens if they screen positive?
- called for further investigation
- will either be positive again (WILL HAVE CANCER)
- or will be negative
- if positive, send for biopsy
- if malignant = TRUE POSITIVE
- if benign = FALSE POSITIVE (bc not acc cancer lol)
- for the malignant, start treatment
What are the consequences of screening?
- detection of cases early
- more are detected early but at cost of individuals who don’t have disease but have to still undergo tests e.g. false positives
- health service needs to cope with increasing demand of managing positive screening results
What are the 3 main things performances are summarised by?
- DETECTION RATE
- FALSE POSITIVE RATE
- OAPR
- PPV
What is detection rate?
- how sensitive the detection is
- proportion of affected individuals (i.e. with disease) that have a screen positive test result
- the number of people that got detected to have the disease over the the total number of people with the disease (i.e. the ones that have disease but weren’t detected+ the detected disease ones)
- percentage
What is false positive rate?
1- specificity
- proportion of unaffected individuals (i.e. healthy
individuals) that have a screen positive test result
What is OAPR?
odds of being affected given a positive result
- out of people who have positive test results, what is the ratio between number of affected individuals to the number of unaffected individuals
What is PPV?
- positive predictive value
- probability
- Number of affected individuals screen positive results/
Total number of people with screen positive results
What is specificty?
1- FPR (false positive rate)
What is OAPR for ovarian cancer?
- OAPR (or PPV) are pretty high
- But 30% of screen positive women have further investigative techniques, which are quite invasive and don’t have cancer
o laparoscopy / laparotomy / oophorectomy
• 50% of cases of ovarian cancer not picked up by screening test
• It is likely that a population screening programme would perform less well
What is the point of screening?
- NOT A DIAGNOSIS
- filtering people into high risk groups
- high enough to want further investigations
What do you need for a worthwhile screening programme?
- Disorder - Well defined medically
- Prevalence - Known & of public health importance
- Natural - Possible to identify early disease from healthy
- History- Need to know how the disease is progressing
- Treatment- Effective treatment is available to all
- Test- should be simple, safe, easily implemented, acceptable
- Test Performance- expected performance of the screening test must be known
• Ethical
o Adequate health provision for the extra clinical workload resulting from the screening
o There are consequences on doing invasive procedures on those who do not actually have the disease
• Access- people who could benefit should have access to the test
• Financial
o Cost-effective – do we prolong life? Is there a better quality of life? Do the hazards outweigh the benefits?
o Early detection & treatment vs. late diagnosis & treatment
o Costs should be balanced against: -
o risks- hazards associated diagnostic test, interventions / treatment
o benefits - reduction in morbidity or mortality
How common is malignant melanoma in the UK?
- 5th most common
- 4% of all new cases
How many new melanoma cases are there each year?
- 15,000 new cases of melanoma skin cancer in UK every year
Why aren’t there any screening tests available for melanoma?
- No accurate screening test available
- No general screening programme in the UK for
malignant melanoma - would examine everyone for abnormal moles
- takes up time
- lot of money
- people would be having unnecessary surgery
What is the prevention strategy for melanoma?
- slip slop slap = in australia
- • Primary prevention
• Has worked as rates of melanoma are decreasing in the children age group
How common is spina bifida?
- 2/1000 births per year
What is the test for spina bifida?
- Alpha-fetoprotein (AFP) is measures in mother’s blood
- Levels tend to be high in affected pregnancies
What is the risk for spina bifida?
- if have high AFP (>2MoM)= high risk
- MoM= multiple of median
- express AFP in relation to median in unaffected pregnancies it’s simply the scale used for AFP
