Principles, methods, applications and organisation of screening for early detection, prevention, treatment and control of disease

Definitions:

“Screening is the process of identifying healthy people who may be at increased risk of disease or condition.  The screening provider then offers information, further tests and treatment. This is to reduce associated risks or complications” (UK National Screening Committee https://www.gov.uk/guidance/nhs-population-screening-explained).

Or

Screening refers to the use of simple tests across an apparently healthy population in order to identify individuals who have risk factors or early stages of disease, but do not yet have symptoms (WHO).

 

Principles:

The underlying concept of screening is that early detection of risk factors or early disease is beneficial for the clinical or public health outcome. Box 3.1.1 below outlines the classic Wilson and Jungner criteria formulated to assess whether a condition potentially warrants screening efforts.

 

Box 3.1.1 Wilson and Jungner classic screening criteria, WHO 1968

  1. The condition sought should be an important health problem.
  2. There should be an accepted treatment for patients with recognised disease.
  3. Facilities for diagnosis and treatment should be available.
  4. There should be a recognisable latent or early symptomatic stage.
  5. There should be a suitable test or examination.
  6. The test should be acceptable to the population.
  7. The natural history of the condition, including development from latent to declared disease, should be adequately understood.
  8. There should be an agreed policy on whom to treat as patients.
  9. The cost of case-finding (including diagnosis and treatment of patients diagnosed) should be economically balanced in relation to possible expenditure on medical care as a whole.
  10. Case-finding should be a continuing process and not a 'once and for all' project.

 

Wilson JMG, Jungner G. Principles and practice of screening for disease. Geneva: WHO; 1968. Available from: 

http://apps.who.int/iris/bitstream/10665/37650/17/WHO_PHP_34.pdf  
 

The key questions to ask when deciding on whether to screen for a health problem are listed in Box 3.1.2.

 

Box 3.1.2

The disease

Is it an important health problem?

Is the natural history well understood?

Is there a long time between the presence of risk factors/sub-clinical disease to overt disease?

Does early intervention improve clinical/public health outcome?

Screening test

Is the test valid (sensitivity and specificity)?

Is the test simple, reliable and affordable?

Is the test acceptable to patient and staff?

Diagnosis and treatment

Is access to diagnostic facilities available and rapid?

Is treatment effective and accessible?

Is it cost-effective?

Is it sustainable?

Does benefit outweigh the harm?

For the assessment and evaluation of screening programmes see the specific section in this chapter.

 

Limitations of screening

Screening has important ethical differences from clinical practice as the health service is targeting apparently healthy people and offering to help individuals make better informed choices about their health. However, there are risks involved and it is important that people have realistic expectations of what a screening programme can deliver. Whilst screening has the potential to save lives, and/or to improve quality of life through early diagnosis of serious conditions, it is not a fool-proof process.

Screening can reduce the risk of developing a condition or its complications, but it cannot offer a guarantee of protection. In any screening programme, there is an irreducible minimum of false positive results (wrongly reported as having the condition) and false negative results (wrongly reported as not having the condition). The UK National Screening Committee is increasingly presenting screening as risk reduction to emphasise this point (https://www.gov.uk/guidance/nhs-population-screening-explained).

 

Brief overview of current UK screening programmes

For detailed information and updates on current programmes please visit the UK Government webpages: 
https://www.gov.uk/topic/population-screening-programmes

Tables A, B and C amended from 'Mastering Public Health: A postgraduate guide to examinations and revalidation. Lewis GH, Sheringham J, Kalim K, Crayford, TJB. London: Royal Society of Medicine Press Ltd; 2008' provide a brief overview of the current UK screening programmes.

 

Table A:  Antenatal screening programmes

Early Pregnancy

Screening for the following conditions is offered to all women:
• Anaemia • Bacteriuria • Blood group and rhesus D status • HBV (Hepatitis B virus) and HIV • Syphilis  • Sickle cell disease and thalassaemia (in high prevalence areas)

Trisolmy abnormalities (Down's, Edwards' and Patau's syndromes)

The combined test is available to women who attend screening in the first trimester (10+0 and 14+1 weeks’ gestation). It is the most effective early screening test for Down’s, Edwards’ and Patau’s syndromes available on the NHS.  It is based on combining an ultrasound measurement of nuchal translucency (NT; thickness of fluid at the nape of the fetal neck as assessed on ultrasound), and serum levels of human chorionic gonadotrophin (hCG), pregnancy-associated plasma protein A (PAPP-A) and the woman's age

If a mother presents late for Down’s syndrome screening, but is in the second trimester between 14+2 and 20+0 weeks’ gestation, then they are offered the quadruple blood test.  Please note, this is for Down’s syndrome screening only.   This blood test consists of measurement of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), hCG, inhibin-A and the woman's age.  This test is less effective than the combined test. 

Based on the results from the screening tests, a risk result can be calculated.  If the pregnancy is deemed to be higher risk (>1/150 risk of carrying an affected baby) then the woman is offered amniocentesis (or chorionic villous sampling [CVS] if <13 weeks' gestation). These are diagnostic tests.

Ultrasound scans

 

The first scan is usually performed between 11 and 14 weeks to date the pregnancy, check that the heart is beating and check to see if it is a single or multiple pregnancy.

Fetal anomaly scan: This is performed at 18−20 weeks' gestation to identify structural anomalies in the fetus, e.g. cleft lip, serious cardiac abnormalities and many more.

 

Table B:  Newborn screening programme

Blood spot screening

(Heel-prick test)

 

 

Screening test carried out when babies are 5 days old.  Used to test for:

o    Phenylketonuria (PKU)

o    Medium-chain acyl-CoA dehydrogenase deficiency (MCADD)

o    Maple syrup urine disease (MSUD)

o    Isovaleric acidaemia (IVA)

o    Glutaric aciduria type 1 (GA1)

o    Homocystinuria (HCU)

Hearing screening programme

Most babies tested in the first week of life or as soon as possible after that. The aim is to offer within 4-5 weeks of birth.  Two screening tests might be offered: Oto-acoustic emissions test or attenuated brain-stem audiometry.

Physical examination (England and Scotland only)

 

 

Offered during first 72 hours of life and once again at 6-8 weeks of birth to detect, amongst others:
  • Congenital heart disease
  • Congenital cataract
  • Congenital malformation
  • Developmental dysplasia of the hip

 

Table C:  Adult screening programmes

Disease

Screening Test

Confirmatory Test

Age group

Frequency

Breast cancer

Mammography

Test may include further imaging (mammography or ultrasound), clinical examination, biopsy

Women aged 50−70 (first invitation always before age 53.)

Women over 70 can request screening every 3 years.

In some areas, age extensions are being trialed where women aged 47 to 49 and 71 to 73 are being invited to screening.

3-yearly

Cervical cancer

Smear test using liquid-based cytology.

Across the UK the national programmes are moving towards primary HPV testing.

Colposcopy

Women aged:

• 25−49 years

• 50−64 years

 

• 3-yearly

• 5-yearly

Bowel cancer

Faecal occult blood test. Moving to using FIT (immunochemical) testing as the firs line test.

(bowel scope screening is also being trialed in some areas of England involving a one-off flexible sigmoidoscopy offered to men and women aged 55 years)

Colonoscopy

In England, Wales and Northern Ireland, men and women aged: 60−74 years

 

In Scotland, men and women aged:

50–74 years

• 2-yearly

 

 

• 2-yearly

Diabetic eye

 

 

Digital image of the retina

Hospital Eye Services/Treatment Services review

Everyone with type 1 and type 2 diabetes aged 12 years or more

1-yearly

Abdominal Aortic Aneurysm (AAA)

 

 

 

 Abdominal ultrasound scan Vascular surgical review including CT scan

Men aged 65 years

Men aged over 65 who have not been screened before can self refer

 One-off screen

 

© Dr Murad Ruf and Dr Oliver Morgan 2008, Dr Kelly Mackenzie 2017