Week 2 Flashcards
What is screening
Screening is a process of identifying apparently healthy people who may be at increased risk of a disease or condition. They can then be offered information, further tests and appropriate treatment to reduced their risk and/or any complications arising from the disease or condition.
Screening leads to early detection of: disease, pre-cursor for disease, susceptibility to disease
Screening can be done by:
Questionnaire (e.g. Geriatric Depression scale)
Examination (e.g. BP measurement)
Lab test (e.g Pap smear)
Imaging (e.g. mammography)
Result of applying a screening test
Disease +:
Test + = true positives
Test - = false negatives
Disease -:
Test + = false positives
Test - = true negatives
Important test characteristic:
- sensitivity: Rate of TPs - the proportion of diseased people identified as diseased
- specificity: rate of TNs- the proportion of healthy people identified as healthy
Sensitivity
How good the test is at picking up the disease
What is the effect of a highly sensitive test on false negatives. Fewer false negatives
a highly sensitive test more useful when the result is negative?
Sensitivity= true positives/ (true positives + false negatives)
Specificity
How good the test is at correctly excluding people without the condition
What is the effect of a highly specific test on false positives. Fewer false positives
a highly specific test more useful if result is positive
Specificity= true negatives/ (false positives+ true negatives)
High specificity and high sensitivity
High specificity important for screening where the consequences of misclassifying someone falsely as diseased are serious. Eg TOP for Down’s syndrome
High sensitivity important for screening where the consequences of missing disease are serious eg transfusion with HIV +ve blood
Effect of screening on individual
Sensitivity and specificity tells us only how good the test is at picking up or excluding disease
However, when we have the best possible test:
- if you test positive, how likely is it that you really have the disease
- if you test negative how likely is it that you really dont have the disease
For these questions, we need to know the predictive values
Predictive values
Positive predictive value (PPV)- if you test positive how likely is it that you really have the disease
PPV= true positive/ (true positive + false positive)
Negative predictive value NPV- if you test negative how likely is it you dont have the disease
NPV= true negatives / ( false negatives+ true negatives )
Prevalence of disease
Prevalence= (true positives + false negatives)/ (true positives+ false positives + false negatives + true negatives)
Who benefits from screening
Every outcomes has set of risks
The benefits must outweigh the harm caused by a screening programme
True positives= labelling
False negatives= false reassurance, disregard symptoms, delayed intervention
False positives= costs of further tests, risks of diagnostic testing, anxiety, fear of future screening
True negatives= costs and risks of screening programme
Screening in the UK
National screening committee:
- advises ministers- all aspects screening policy
-latest research evidence, multi- disciplinary expert groups, patient and service users
- Assess proposed new screening programmes against criteria to ensure they do more good than harm at reasonable cost
Natural history of disease
Condition worth screening only if we understand natural history
To make it worthwhile we need:
1- pre clinical detectable period
2- test that can be applied
3- treatment that will alter outcome
Criteria used by the NSC
The condition:
- important, has latent phase, natural history understood, primary prevention implemented
The test:
-suitable (simple, safe,precise, valid, acceptable), agreed suitable cut offs, agreed policy for test +ve
The intervention:
- effective treatment, policy on who to treat, adequate facilities
The screening programme:
- RCT evidence of effectiveness, info understandable by those screened, clinically, socially and ethically acceptable, benefits vs harms, value for money
Implementation of programme:
- clinical management and patient outcomes should be optimised, all other options considered, plan for monitoring programme, adequate staffing and facilities
Evaluation of screening programmes
If compare outcomes (eg survival times) in patients identified by screening to those identified clinically biases can occur:
-volunteer bias
-lead time bias
- length bias
Volunteer bias
Decision to attend screening is general influenced by an individuals health awareness
- do more ‘healthy’ people attend screening programmes
- is lower mortality rate from those who attend screening due to the screening programme or the population who attend screening
- when evaluating screening programmes its important to consider how patients are recruited
Volunteer bias/detection bias
Screened may differ from non screened (usually Lower risk)
Most important where coverage is low
Lead time bias
Time by which diagnosis is advanced because of screening-> apparent increase survival
(I.e the time between disease detection through screening and the disease detection by diagnosis without screening)
Length time bias
Those with long pre clinical phase more likely to be detected by screening and usually have better prognosis (less aggressive disease)
Slowly progressive disease- over represented in “screened cohort”
Rapidly progressive disease- under represented in screening
What is palliative care
About looking after people with incurable illnesses, relieving their suffering and supporting them through difficult times
Palliative- to cloak
Approach that improves the quality of life of patients and their families facing the problem associated with life threatening illness, through the prevention and relied of suffering by means of early identification and impeccable assessment and treatment of pain and other problems physical, psychosocial and spiritual
Palliative care
Provides relief from pain and other distressing symptoms
Affirms life and regards dying as a normal process
Intends neither to hasten or postpone death
Integrates the pyschological and spiritual aspects of patient care
Offers a support system to help patients live as actively as possible until death
Offers a support system to help the family cope during the patients illness and in their own bereavement
Uses a team approach to address the needs of patients and their families including bereavement counselling if indicated
Will enhance quality of life and may also positively influence the course of illness
Is applicable early in the course of illness, in conjunction with other therapies that are intended to prolong life such as chemotherapy or radiation therapy and includes those investigations needed to better understand and manage distressing clinical complications
