Health Screening

Question 1

What’s overdiagnosis?

Answer 1

Correct diagnosis of a disease, but the diagnosis is irrelevant as the disease will never cause symptoms within the patients lifetime

Question 2

What’s overtreatment?

Answer 2

Unecessary treatment which does not improve health

Question 3

What are two big issues with screening?

Answer 3

Over diagnosis and therefore over treatment

Question 4

Why is overdiagnosis is an ethical problem in screening?

Answer 4

Causing emotional harm to a patient who otherwise wouldn’t be harmed

Question 5

Outline the neuroblastoma case for screening issues

Answer 5

Japan screened and found higher % survival rate, however number of deaths remained unchanged
= overdiagnosing

Question 6

What’s the problem with breast cancer screening?

Answer 6

Overscreening harms many more (unnecessarily) than the lives it saves
Women go through unnecessary emotional harm and surgery/radiotherapy

Question 7

What’s important to consider when a patient requests screening?

Answer 7

Life years vs QoL

Question 8

What’s the popularity paradox with regards to screening?

Answer 8

The more people you screen, the more people are harmed by overdiagnosis, but the more popular the screening programme becomes

Question 9

What are the WHO criteria for disease screening? (Wilson and Jungner criteria)

Answer 9

The condition should be an important health problem

There should be a treatment for the condition

Facilities for diagnosis and treatment should be available

There should be a latent stage of the disease

There should be a test of examination for the condition

The test should be acceptable to the population

The natural history of the disease should be adequately understood

There should be an agreed policy on whom to treat

The total cost of finding a case should be economically balanced in relation to medical expenditure as a whole

Case-finding should be a conditions process not just a once and for all project

Question 10

What are antenatal and newborn UK screening programmes?

Answer 10

Down’s syndrome
Feral anomaly ultrasound scan
Infectious diseases in pregnancy
Antenatal sickle cell and Thalassaemia
Newborn and infant physical examination
Newborn blood spot
Newborn hearing screening

Question 11

What are UK screening programmes in young persons/adults?

Answer 11

AAA
Diabetic Retinopathy
Breast cancer
Cervical cancer

Question 12

What’s a true positive compared to a true negative test result?

Answer 12

True positive = patient correctly diagnosed

True negative = patient doesn’t have disease and is correctly diagnosed as not having it

Question 13

What are false positive and negative results?

Answer 13

False positive = patient doesn’t have a disease but the screening test is positive so patient is falsely worried

False negative = patient has disease but test doesn’t diagnose it, so patient is falsely reassured

Question 14

What’s the difference between sensitivity and specificity?

Answer 14

Sensitivity = proportion of people who have the disease that the test correctly detects

Specificity = proportion of people who don’t have the disease that the test correctly identifies as not having the disease

Question 15

What are the equations for sensitivity and specificity?

Answer 15

Sensitivity = true positive / (true positive + false negative)

Specificity = true negative / (true negative + false positive)

Question 16

What are the positive and negative predictive values?

Answer 16

Positive predictive value = probability that a person has disease given that they have had a positive test result

Negative predictive value = probability that a person doesn’t have a disease given they have a negative test result

Question 17

If prevalence is reduced, what happens to the positive predictive value?

Answer 17

If prevalence is reduced, then positive predictive value is reduced

A greater number of people will have to be recalled for further tests to detect each case of disease

Question 18

What are 4 common types of bias in screening programmes?

Answer 18

Healthy screen
Length time effect
Lead time effect
Overdiagnosis

Question 19

Why do people who attend screening tend to live longer, even if the screene was useless?

Answer 19

People who choose to attend screening tend to be healthier than those that don’t
People who don’t take up invitations to screen are more likely to be smokers, drinkers, low income, poor diet, existing medical conditions

= comparisons between self selected screened and unscreened groups are biased

Question 20

What’s lead time bias in screening?

Answer 20

Screening can detect illness earlier = more responsive to treatment = improve survival times

But

Useless screening can appear to increase survival time by detecting disease earlier but not actually resulting in longer life

Question 21

What’s length time bias in screening?

Answer 21

Screening is better at detecting disease that develops more slowly
Disease that develops more slowly means that you live for longer
= screen detected disease likely to have better prognosis even if it results in no difference in treatment