Block 10 Flashcards
What is sensitivity?
Measures proportion of positives that are correctly identified (true positives)
What is specificity?
Measures proportion of negatives that are correctly identified (true negatives)
Uses of a Diagnostic Test
- Diagnosis
- Monitoring
- Screening
- Prognosis
What is a diagnostic test?
Any medical test that aids diagnosis/ detection of disease
What is positive predictive value?
The probability that subjects with a positive screening test truly have the disease
What is a negative predictive value?
The probability that subjects with a negative screening test truly do not have the disease
What is the likelihood ratio?
Likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that the same result would be expected in a patient without the target disorder
What is screening?
Systematic application of a test to identify individuals at risk of a specific disease, to warrant further investigation/ prevention, amongst people who have not sought medical attention on account of symptoms of that disorder
Purpose of screening
- If primary prevention is limited
- If opportunity for treatment is limited
- Gives potential for early diagnosis and so more effective treatment
Diseases that are commonly screened for
- Cancer - colorectal/ breast/ cervical
- PPD Test - TB
- Prenatal test - foetal abnormality
- Newborn bloodspot test - PKU/ cystic fibrosis etc.
- Ophthalmamoscopy or digital photography and image grading - diabetic retinopathy
- Ultrasound scan - abdominal aortic aneurysm
- Screening for metabolic syndrome
- Screening for potential hearing loss in newborns
Limitations of screening
- Cost + resources (many do not have disease)
- Adverse effects of screening - radiation exposure, stress
- False positive = stress
- Unnecesary investigation and treatment of false positives
- Stress caused by prolonged knowledge of illness without improvement in outcome
- False security by false negatives
What needs to be evaluated when deciding what to screen for?
- Condition - epidemiology
- Test - effective?
- Treatment - evidence based?
- Programme - RCT evidence of reduction in mortality
What is sojourn time?
Duration of a disease before clinical symptoms become apparent, but during which it is detectable by a screening test
What is length bias?
Overestimation of survival duration among screening-detected cases by the relative excess of slowly progressing cases
What is lead time bias?
Overestimation of survival duration among screen-detected cases (relative to those detected by signs and symptoms) when survival is measured from diagnosis
What is over diagnosis bias?
Overestimation of survival duration among screen-detected cases caused by inclusion of pseudodisease (subclinical disease that would not become overt before the patient dies of other causes)
What is a PSA test?
Detects Prostate specific antigen (PSA) - protein produced by cells of the prostate gland
When is PSA elevated?
Prostate cancer, BPH, Prostasis, UTI
Advantages of PSA screening
- Help detect asymptomatic tumours
- Estimate prostate size and stage
- Helps predict response to treatment
- Used to monitor men at increased risk
Disadvantages of PSA screening?
- Early detection does not reduce death by cancer
- Overdiagnosis = over treatment
- May give false positive
- May give false negative
Impact of incontinence on patient
- Distress
- Embarrassment
- Inconvenience
- Threat to self-esteem
- Loss of personal control
- Desire for normalisation
- Loss of sexual interest
- Difficulty sleeping
Impact of chronic dialysis
- Regular hospital admissions
- Restriction of leisure time
- May have to give up job
- Increased dependence on dialysis
- Uncertainess about future
- Fatigue
- Limitation of liquids + food
- Disrupts family and friend relationships
- Depression
- Low self-esteem
4 sources used when making a clinical decision
Patient preference
Available resources
Research evidence
Clinical expertise
What is opportunity cost?
Amount of money that is alienated by choosing to use it for one project rather than another
