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Concepts of Screening. Helena Kemp Consultant Chemical Pathologist North Bristol NHS Trust. Outline of talk. The definition & principles of screening National screening policy The screening ‘test’ The screening ‘programme’ Quality management Public & professional education

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concepts of screening

Concepts of Screening

Helena Kemp

Consultant Chemical Pathologist

North Bristol NHS Trust

outline of talk
Outline of talk
  • The definition & principles of screening
  • National screening policy
  • The screening ‘test’
  • The screening ‘programme’
  • Quality management
  • Public & professional education
  • A model of screening - MCADD
  • The balance of harm vs benefit
definition of screening
Definition of Screening

‘The systematic application of a test or enquiry to

identify individuals at risk of a specific disorder

to warrant further investigation or direct

preventative action, amongst persons who have

not sought medical attention on account of

symptoms of that disorder. ‘

principles of screening wilson and jungner 1968
Principles of ScreeningWilson and Jungner 1968
  • The condition is an important health problem
  • Its natural history is well understood
  • It is recognisable at an early stage
  • Treatment is better at an early stage
  • A suitable test exists
  • An acceptable test exists
  • Adequate facilities exist to cope with abnormalities detected
  • Screening is done at repeated intervals when the onset is insidious
  • The chance of harm is less than the chance of benefit
  • The cost is balanced against benefit
screening in the uk
Screening in the UK

Improving Screening: A Public Health Task for the

Nineties Public Health Network – March 1994

- Variations in policy, including no policy

- Variations in practice

- Absence of standards

- Absence of performance measurement

- Patchy training

- Poor patient information

- No clear lines of accountability

the uk national screening committee
The UK National Screening Committee
  • Established 1996
  • The UK National Screening Committee advises Ministers, the devolved National Assemblies and the Scottish Parliament on:
    • The case for implementing new population screening programmes.
    • Screening technologies
    • The case for continuing, modifying or withdrawing existing population screening programmes
  • Set up practical mechanisms to oversee the introduction & implementation of a new programme in the NHS & monitor effectiveness and quality assurance

Consumer groups

HTA Population


Advisory groups egg

Child Health Subgroup

and antenatal Subgroup

DH Policy Research



Royal Colleges

Other sources of

evidence e.g. MRC

Professional organisations

NHS managing

clinical innovations


revised definition of screening
Revised definition of screening

‘Screening is a public health service in which members of a defined population, who do not necessarily perceive they are at risk of, or are already affected by a disease or its complications, are asked a question or offered a test, to identify those individuals who are more likely to be helped than harmed by further tests or treatment to reduce the risk of a disease or its complications’.

uk national screening committee revised criteria 2003 www nsc nhs uk pdfs criteria pdf
UK National Screening Committee revised criteria
  • Appraise the viability, effectiveness and appropriateness of a screening test
  • Additional criteria:
    • Requirements of screening programmes which include mutation analysis
    • Evidence base i.e. Randomised Controlled Trial data to indicate that screening programme effectively reduces mortality or morbidity
    • Quality management of screening programmes
    • Provision of information for informed choice to participate
nsc screening policies www nsc co uk
NSC screening
  • Nationally managed programme
    • e.g. Antenatal Downs screening, Newborn CF, Breast Cancer
  • Planned National programme
    • e.g National Chlamydia Screening Programme
  • Screening - with reservations
    • e.g. Prostate Cancer (Prostate Cancer Risk Management Programme)
  • Under review
    • e.g. abdominal aortic aneurysm men over 65 years
  • Not recommended
    • e.g. antenatal CF, CAH, bladder cancer

UK National Screening Committee

Programmes Director, Sir Muir Gray

Vascular Screening

Cancer Screening Programmes

Fetal, Maternal & Child Health subgroup (FMCH)

Vascular Diseases Risk Management



Sickle Cell and Thalassaemia Screening

Down‘s Syndrome


Fetal Anomaly




Diseases; HIV, Hepatitis B, Syphilis, Rubella

Newborn Blood spot screening

Cystic Fibrosis screening

Newborn and 6-8 week Infant Physical Examinations

Newborn Hearing Screening





Bowel Cancer


NSC Organisational Structure

the screening test
The screening test
  • An enquiry e.g. ethnicity
  • An examination e.g. 6-8 wk physical examination
  • An investigative procedure e.g. fetal anomaly scanning
  • A single analytical test e.g. phenylalanine PKU
  • Multiple markers
    • Multivariate risk calculation
    • Multi protocol
assessing the performance of a screening test
Assessing the performance of a screening test

Sensitivity = a / a + c

Specificity = d/ b + d

Positive predictive value = a/ a + b

Negative predictive value = d/ c + d

performance of a screening test
Performance of a screening test
  • Detection rate (sensitivity)

The proportion of affected individuals with a positive result

  • False positive rate (specificity = 1-FPR)

The proportion of unaffected individuals with a positive result

  • Positive predictive value

The chance that those with a positive test result are affected

  • Performance will depend on cut-off levels chosen
  • Cut–off chosen will be influenced by many factors including

justification for further tests and resources

screening programmes
Screening programmes
  • Systematic
    • Breast cancer, newborn bloodspot
  • Opportunistic
    • STI
  • Targeted
    • Tay sachs ashkenasi jewish population
newborn bloodspot screening
Newborn bloodspot screening


Obtaining informed consent Child, family, midwife

Taking the sample Midwife

Sending sample to lab Midwife


Primary screening test Screening lab

Second tier tests Screening & referral labs

Interpretation and reporting Screening lab consultant

Post analytical

Checking coverage Child Health Department

Reporting normal results to parents Health visitor

Confirmation of positives Specialist paediatrician

Genetic counselling Genetic Nurse/midwife

principles of quality management for screening nuffield institute of health march 2000
Principles of quality management for screeningNuffield Institute of Health March 2000
  • A clear coherent framework of objectives, standards & guidance
  • A culture of learning, not blame
  • A partnership with staff and users
  • Continuous quality improvement
  • Clear management structures
  • Effective & efficient performance measurement
  • Adequate systems & resources
  • Bridging the expectation gap
the uk newborn screening programme centre est 2002

Set process standards

coverage, timeliness,

communication of results,

referral standards


for parents and





Policy for blood

spots retention

Policy for parental consent


The UK Newborn Screening Programme Centre (est. 2002)
process standards newborn bloodspot screening
Timely sample collection

Timely sample dispatch

Completeness of coverage

Enhanced tracking abilities

Timely notification of unscreened babies

Timely processing of positive screening samples

Process standards Newborn bloodspot screening
laboratory quality standards newborn sickle cell screening
Laboratory quality standards newborn sickle cell screening
  • Accreditation by an appropriate body (e.g. CPA).
  • Consultant led service with defined lines of responsibility for all laboratory aspects of the service.
  • HPLC & IEF methodology with a different technique for confirmation from initial screen.
  • Appropriate internal quality control undertaken and documented
  • Compulsory participation in an accredited EQA appropriate for newborn screening (NEQAS scheme)
  • Provision of information on screening performance to monitoring groups (NSC, NPC).
  • Workload should exceed 25,000 specimens per year (ideally 50,000).
education resources for hcp
Education resources for HCP
  • Internet resources
    • Programme specific training material
  • Educational programs
    • NSC commissioned professional training for informed choice
  • Other Resources
    • Cards for Midwives
a model of screening mcadd
A model of screening -MCADD
  • Evidence base
  • Pilot study
  • Assessment against NSC criteria
  • Ministerial announcement Feb 2007
  • Implementation
Extended newborn screeningNewborn Screening with Tandem MS - New South Wales, Australia B Wilcken et al NEJM 2003; 348:2304-12
  • 4 years experience 1998-2002
  • 362,000 newborns screened
  • 31 disorders detected, 57 babies (15.7 per 100,000 screened)
      • Urea cycle 7
      • Amino acid disorders 9
      • Organic acid disorders 12
      • Fatty acid oxidation disorders 29
        • SCAD 5
        • MCAD 17
        • VLCAD 3
        • Carnitine defects 4

Effect of Expanded Newborn screening for biochemical genetic disorders on child outcomes and parental stressWaisbren et al JAMA 2003 290 2564-2572

  • Prospective study of expanded screening 1999-2002
  • Participants
    • 50 affected families – identified by NS
    • 33 affected families - clinically diagnosed
    • 94 false positive children
    • 81 screen normal children
  • Main outcome measures
    • Child’s health and development
    • Parental Stress index
  • Cases identified by newborn screening vs clinical diagnosis
    • 28% NS vs 55% clinically identified required hospitalisation
    • 1 NS vs 8 clinically identified children severe learning difficulties
    • Mothers in screened group reported lower stress on PSI than mothers in clinically identified group
  • False positive group vs normal screening result
    • 21% children with false positive results vs 10% hospitalised
    • Mothers in false positive group attained higher scores on PSI
    • Mothers in false positive group attained higher scores on Parent child dysfunction subscale
false positives in expanded newborn screening
False positives in expanded newborn screening
  • Prevalence of true positives
    • 1 in 2400 infants screened (0.04%)
  • Prevalence of false positives
    • 1 in 300 infants screened (0.33%)
  • 8 false positives for every true positive
  • Approx 13,000 false positives/year

A review of the psychosocial effects of false positive results on

parents and current communication practices in newborn screening

Hewlett & Waisbren JIMD 2006 29:677-682

useful resources
Useful resources
  • Downs screening
  • Newborn screening
  • Sickle cell and thalassaemia