Block 10 Flashcards
Sensitivity
True positives
Equation for sensitivity
TP/TP+FN
Specificity
True negatives
Eq for specificity
TN/TN+FP
Diagnostic test
Any medical test performed to aid the diagnosis or detection of disease
4 uses of diagnostic tests
Diagnosis
Monitoring
Screening
prognosis
Importance of sensitivity and specificity in informing diagnosis
importance of diagnostic accuracy in testing is directly proportional to the tests potential to cause patient consequences and harm
true positive
test indicates disease when there is disease
true negative
test indicates no disease when there is no disease
false negative
test indicates no disease when there is disease
false positive
test indicates disease when there is none
positive predictive value
probability that subjects with a positive screening test truly have the disease
negative predictive value
probability that subjects with a negative screening test truly dont have the disease
likelyhood ratio
likelyhood that a given test result would be expected in a patient with the target disorder compared to the likelyhood that the same result would be expected in a patient without the target disorder
screening
systematic application of a test to identify individuals at sufficient risk of a specific disorder to warrant further investigation or direct preventative action, amongst people who have not sought medical attention on account of any symptoms of that disorder
purpose of screening
opportunities for primary prevention and treatment are limited, gives potential for early and more effective treatment
which cancers commonly screened for
colorectal, breast, cervical
what does the PPD test screen for
Tuberculosis
prenatal blood tests for
foetal abnormalities
newborn bloodspot test for
sickle cell, CF, congenital hypothyroidism, metabolic disease (PKU, MCADD, etc.)
Opthalmascopy screens for
diabetic retinopathy
ultrasound screens for
AAA
limitations of screening
cost/resources - majority don’t need treatment
adverse effects
stress from FP
unnecessary treatment of FP
stress from prolonging illness with no treatment outcomes
false sense of security from FN
pros of good screening
early detection of the disease can reduce the risk of death or illness for some people
cons of screening
some people get tests, diagnosis and treatment with no benefit, some people get ill or die despite negative screen
areas for evaluation when deciding what should be screened for
condition, test, treatment, programme
Condition factors
important? epidemiology, natural hustory, detectable risk factor, latent period, cost-effective
test factors
simple, safe, precise, validated cut off agreed, acceptable
treatment factors
effected EB treatment
programme factors
RCT evidence of reduction of mortality/morbidity, benefit outweigh harm, opportunity cost, quality assurance
sojourn time
duration of a disease before clinical symptoms become apparent but during which it is detectable by a screening test
short sojourn time
rapidly progressing disease, poorer prognosis
length bias
overestimation of survival duration among screening-detected cases by the relative excess of slowly progressing cases
consequences of length bias
diseases with longer sojourn time easier to detect through screening,
on average people with disease detected through screening have better prognosis than through S&S,
comparing individuals choosing screened to those not gives distorted picture
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
consequences of lead time bias
survival inevitably longer following diagnosis through screening because of the ‘extra’ lead time.
as a result of this the appropriate measure of effectiveness is deaths prevented, not survival
overdiagnosis bias
overestimation of survival duration among screen-detected cases caused by inclusion of pseudodisease
pseudodisease
subclinical disease that would not become overt before the patient dies of other causes
when does overdiagnosis bias occur
when screen-detected cancers are either non-growing or so slow-growing that they would never cause medical problems
PSA testing
prostate specific antigen - protein produced by cells of the prostate gland
PSA elevated in
prostate cancer, BPH, prostatis, UTI
advantages of PSA screening
can help detect tumours with no symptoms, allows estimation of prostate size and stage, helps doctor predict response to treatment, can be used to monitor men at increased risk
disadvantages of PSA screening
early detection may not reduce chance of dying from prostate cancer, over diagnosis -> overtreatment, may give FP (not specific enough) or FN
impacts of incontinence on a patient
distress, embarrassment, inconvenience, threat to self esteem, loss of personal control, desire for normalisation, loss of interest in sex, difficulty sleeping
impact of chronic dialysis on patients
regular hospital admissions, restriction of leisure time, may have to give up job, increased dependance on dialysis, uncertainness about future, fatigue, limitation of liquids and foods, disrupts relationships, depression, lower self esteem
4 sources used when making a clinical decision
PARC patient preferences, available resources research evidence clinical expertise
opportunity cost
loss of other alternatives when one alternative is chosen, amount of money that is alienated by choosing to use it for one project rather than another
distributed justice
how we distribute finite resources fairly
how to decide ways to distribute healthcare
QALY calculation, waiting list, likelihood of complying with treatment, Pt lifestyle choices, ability to pay
confidentiality
pledge of agreement to not divulge or disclose information about patients to others
importance of maintaining confidentiality
improves trust between pt and dr, respects autonomy, prevents pt harm, virtuous, human rights act, GMC requirement
when can confidentiality be breached
statute (law), consent by patient, public best interest
laws which oblige doctors to disclose info
public health act 1984
road traffic act 1988
prevention of terrorism act 1989
