Screening

Question 1

DIsease prveention - high risk vs population wide approach

Question 2

What is population screening

Answer 2

• Population screening refers to a test that is offered to all individuals in a target group, usually defined by age, as part of an organised program.
• Screening is the process of identifying healthy people who may have an increased chance of a disease or condition.

The screening provider then offers information, further tests and treatment. This is to reduce associated problems or complications

Question 3

UK Breast screenign program

Answer 3

Question 4

Primary/secondary/tertiary prevention

Answer 4

• Primary prevention - prveent onset of disease
• Secondary prevention - aims to halt the progression of disease once established
• Tertiary - aims to prevent progression of disease once established

Question 5

Examples of population screening porgrams

Answer 5

• NHS abdominal aortic aneurysm (AAA) programme
• NHS bowel cancer screening (BCSP) programme
• NHS breast screening (BSP) programme
• NHS cervical screening (CSP) programme
• NHS diabetic eye screening (DES) programme
• NHS fetal anomaly screening programme (FASP)
• NHS infectious diseases in pregnancy screening (IDPS) programme
• NHS newborn and infant physical examination (NIPE) screening programme
• NHS newborn blood spot (NBS) screening programme
• NHS newborn hearing screening programme (NHSP)
• NHS sickle cell and thalassaemia (SCT) screening programme
• Population screening: data and intelligence
• Population screening: evidence and guidance
• Population screening: quality assurance

Question 6

Abdominal aortic anerysm screening

Answer 6

• Abdominal aortic aneurysms (AAAs) are bulges in the main blood vessel in the abdomen.
• An AAA that gets too large can burst (rupture), an event that is usually fatal. Although AAAs do not usually cause
• any symptoms and are unlikely to cause problems until they burst, they can be easily diagnosed by simple
• ultrasound screening. In the UK, men aged 65 years are offered ultrasound to look for an AAA, and just
• over 1 in 100 men who are screened are found to have an AAA. If the AAA is large, men are offered
• an operation to prevent the aneurysm bursting; if it is small, they are offered regular scans to monitor
• their AAA.

Question 7

What is prevalence, sensitivity,specifcity, positive/negativ epredictive value and likelihood ratio

Answer 7

• Prevalence of breast cancer in this screened population. The true positives (86) + the false negatives (14) divided by all the population (10000). In this case 1%
• The sensitivity: How good is the test at detecting breast cancer where it is present? It is the True positives (86) divided by the true positives (86) + the false negatives (14). Therefore, in this case 86%.
• The specificity: How good the test is at identifying those who do not have breast cancer? It is the true negatives (9300) divided by the true negatives (9300)+ false positives (600). In this case 94%.
• The positive predictive value is the probability that some one who tests positive on mammogram really does have cancer. It is the true positives (86) divided by the true positives (86) and the false positives (600). In this case 13%
• The negative predictive value is the probability that someone who tests negative really doesn’t have cancer. It is the true negatives (9300) divided by the true negatives (9300) + the false negatives (14). In this case 99.8%.
• The likelihood ratio the likelihood of a test result in a patient with the disease of interest compared to the likelihood of getting that test result in a patient without the disease of interest.
• (LR+) = Sn / (1-Sp) = [a/(a+c)] / [b/(b+d)] = [86/100]/[600/9900] = 14.33