Concepts of screening
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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


Concepts of screening

Consumer groups

HTA Population

ScreeningPanel

Advisory groups egg

Child Health Subgroup

and antenatal Subgroup

DH Policy Research

Programme

NSC

Royal Colleges

Other sources of

evidence e.g. MRC

Professional organisations

NHS managing

clinical innovations

group


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 2003www.nsc.nhs.uk/pdfs/criteria.pdf

  • 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 policieswww.nsc.co.uk

  • 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


Concepts of screening

UK National Screening Committee

Programmes Director, Sir Muir Gray

Vascular Screening

Cancer Screening Programmes

Fetal, Maternal & Child Health subgroup (FMCH)

Vascular Diseases Risk Management

Diabetic

Retinopathy

Sickle Cell and Thalassaemia Screening

Down‘s Syndrome

Screening

Fetal Anomaly

Ultrasound

screening

Infectious

Diseases; HIV, Hepatitis B, Syphilis, Rubella

Newborn Blood spot screening

Cystic Fibrosis screening

Newborn and 6-8 week Infant Physical Examinations

Newborn Hearing Screening

Cervical

Screening

Breast

Screening

Bowel Cancer

Screening

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


Screening algorithm newborn cf screening

Screening Algorithm newborn CF screening


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


Roc curve analysis

Roc curve analysis


Screening programmes

Screening programmes

  • Systematic

    • Breast cancer, newborn bloodspot

  • Opportunistic

    • STI

  • Targeted

    • Tay sachs ashkenasi jewish population


Newborn bloodspot screening

Newborn bloodspot screening

Pre-analytical

Obtaining informed consentChild, family, midwife

Taking the sampleMidwife

Sending sample to labMidwife

Analytical

Primary screening testScreening lab

Second tier testsScreening & referral labs

Interpretation and reportingScreening lab consultant

Post analytical

Checking coverageChild Health Department

Reporting normal results to parentsHealth visitor

Confirmation of positivesSpecialist paediatrician

Genetic counsellingGenetic Nurse/midwife


Integration of screening programmes

Integration of screening programmes


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

Information

for parents and

professionals

PatientRegisters

Training

UKNSPC

Policy for blood

spots retention

Policy for parental consent

Informatics

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).


Parent information

Parent Information


Education resources for hcp

Education resources for HCP

  • Internet resources

    • www.screening.nhs.uk/cpd

    • Programme specific training material

  • Educational programs

    • PEGASUS

    • 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


The balance of harm vs benefit

The balance of harm vs benefit


Concepts of screening

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 disorders9

    • Organic acid disorders12

    • Fatty acid oxidation disorders29

      • SCAD5

      • MCAD17

      • VLCAD3

      • Carnitine defects4


Concepts of screening

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


Results

Results

  • 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

  • www.nelh.nhs.uk/screening

  • www.nsc.nhs.uk

  • www.screening.nhs.uk

  • Downs screening

    • www.nehl.nhs.uk/screening/dssp/home.htm

  • Newborn screening

    • www.newbornscreening-bloodspot.org.uk

  • Sickle cell and thalassaemia

    • www.kcl-phs.org.uk/haemscreening


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