Block 5: Week 2- Screening

Question 1

List UK Major screening programmes for Antenatal & Newborn

Answer 1

• Down’s Syndrome
• Foetal anomaly USS
• Infectiousdiseasesinpregnancy
• Antenatal Sickle cell & Thalassaemia
• Newborn and Infant Physical Exam
• Newborn Blood spot
• NewbornHearing Screen

Question 2

Name some of the Adult Major screening programmes

Answer 2

• AAA
• Breast Cancer
• Cervical Cancer
• BowelCancer
• Diabetic Retinopathy

Question 3

What are the Wilson & Junger Criteria?

Answer 3

Principles of Practice of Screening for Disease

PATHETIC Little Fred

• Policy of who to treat
• Acceptable test
• Treatment exits
• History of disease understood
• Economically balanced
• Test/ Examination exists
• Important health problem
• Case findings should be Continuous Process, not just a once and for all project
• Latent Period
• Facilities for Dx & Tx available

Question 4

Define Overdiagnosis

Answer 4

Correct diagnosis of a disease but diagnosis is irrelevant because the disease will never cause symptoms within pt’s lifetime

Question 5

What is Overtreatment?

Answer 5

Unneccessary Tx which does not improve health

Question 6

What is the Popularity Paradox

Answer 6

The more you overdiagnose people the more popular the screening becomes

Question 7

Define Sensitivity

Answer 7

Proportion of people who have disease that the test correctly detects

(Likelihood that if you have the disease the test will pick up that you have it & get positive result)

Question 8

Define Specificity

Answer 8

Proportion of people who do not have the disease that the test correctly identifies as not having the disease

(Likelihood that if you do not have the disease the test will identify you as disease free)

Question 9

Using Diseae Positive, Disease Negatie, Screening Test positive, Screening Test negative

Draw a table showing how you get: TP, TN, FP, FN

Answer 9

Question 10

How do you calculate specificity?

Answer 10

TP / (TP+FN)

Question 11

How do you calculate sensitivity?

Answer 11

TN/ (TN+FP)

Question 12

Sensitivity & Specificity measure test performace & are ____ of ____ ______ in a population

If you have a disease the senitivity tells you the probability that the test will pick up that disease

BUT: If you test +ve _____ ______ or ____ can tell you the proboabilty that you have the disease. This depends on the disease prevalence

Answer 12

Sensitivity & Specificity measure test performace & are independant of disease prevelance in a population

If you have a disease the senitivity tells you the probability that the test will pick up that disease

BUT: If you test +ve NEITHER sensitivity or specificity can tell you the proboabilty that you have the disease. This depends on the disease prevalence

Question 13

What is PPV?

(positive predictor value)

Answer 13

Probabilty that person has disease given that they’ve had a +ve result

Question 14

What is NPV?

Answer 14

The probability that the person doesn’t have the diease given they’ve had a negative result

Question 15

How do you calculate PPV?

Answer 15

TP/ (TP+FP)

Question 16

How do you calculate NPV

Answer 16

NPV= TN/ (TN+FN)

Question 17

What are the types of bias in screening?

Answer 17

• Healthy Screenee
• Lead Time
• Length Time Bias

Question 18

What is Healthy Screenee Bias?

Answer 18

People that attending screening live longer than those that do not- even if screening is useless

Question 19

What is the lead time bias?

Answer 19

Screening can detect illness earlier when its more responsive to tx

•HOWEVER, USELESS screening can appear to increase survival time by simply detecting the disease earlier but not actually resulting in longer life (eg: you’ve had the diagnosis for longer so appear to live longer post dx)

Question 20

What is the length time bias?

Answer 20

• Screening better @ detecting disease the develop slowly
• Slow developing disease means you live longer
• Therefore, screen detected disease likely to have better prognosis even if it results in no difference in tx

Therefore: Longer lasting, less severe vesions of the diease are more likely to be picked up because more severe ones more likely to kill you before screening. Gives the ilusion of better prognosis post screening