Lecture_10-Screening_2024

Lecture 10 - Screening Overview

  • Presented by Ross Lawrenson at the University of Waikato Medical Research Centre.

Background on Prevention

  • Primary Prevention: Preventing disease from developing by addressing underlying factors.

  • Secondary Prevention: Early identification of disease to change outcomes and improve prognosis.

What is Screening?

  • Investigating healthy individuals to detect unrecognized diseases or precursors.

  • Aim: Apply interventions to high-risk groups for better outcomes at both individual and community levels.

Types of Screening

Mass Screening

  • Entire population invited for testing (e.g., breast screening).

Targeted or Selective Screening

  • Focused on high-risk groups, such as Maori populations at risk for lung cancer.

Single Disease Screening

  • Screening for one specific condition (e.g., breast cancer).

Multiphasic Screening

  • Using tests for multiple conditions simultaneously (e.g., blood tests for several diseases).

Opportunistic Screening

  • Screening individuals who are available, e.g., patients visiting a GP or emergency department.

Opportunistic Screening Programmes

  • Common diseases screened include:

    • Skin Cancer

    • Prostate Cancer

    • Cervical Cancer

    • Diabetes

  • These programmes can be large, but often lack full tracking of screening activities.

Screening Criteria

  • Conditions suitable for screening should have:

    • An effective test.

    • Accessible treatment available.

    • Evidence from trials showing effectiveness in reducing morbidity/mortality.

    • Benefits outweigh harms.

    • Healthcare system capacity for implementation.

    • Consideration of social, ethical, and cost-benefit issues.

Challenges in Screening

  • Perception of screening as a mere test rather than a comprehensive pathway.

  • High public and professional expectations.

  • Issues regarding privacy and data management.

  • Screening programs may not align with individual benefits vs. community health goals.

National Screening Advisory Committee (NSAC)

  • Quickly evolving role instructed to provide advice on:

    • Screening practice effectiveness and feasibility.

    • Social and ethical considerations.

    • Evaluation metrics for screening quality.

    • Resource management for effective screening.

Key Considerations for Conditions Being Screened

Epidemiology

  • Severity, incidence, and prevalence must be known.

Test Characteristics

  • Tests should be simple, safe, sensitive, specific, and valid.

Treatments Available

  • Must have effective and acceptable treatment options; adequate facilities for delivering treatment should exist.

Lead Time and Length Bias

  • Lead Time Bias: Screening can show increased survival not due to effective treatment but early diagnosis.

  • Length Bias: Screening may preferentially detect slower progressing cases, impacting perceived survival benefits.

Examples of Screening

Newborn Screening

  • Guthrie Test for phenylketonuria (PKU) to prevent mental retardation.

  • Tests for several conditions: amino acid disorders, cystic fibrosis, congenital conditions.

Hearing Tests

  • Screening for significant hearing loss in infants can aid early development.

  • Treatment could include hearing aids or cochlear implants.

Down’s Syndrome Screening

  • Trisomy 21 risk is age-related, diagnosed antentally or postnatally.

  • Screening involves Nuchal Translucency scans and blood tests for biochemical markers.

Breast Cancer Screening

  • Free screening offered to women aged 45-69 years every two years.

  • Mammography is sensitive but can have a high false-positive rate.

Cervical Cancer Screening

  • New NHSP focuses on HPV testing rather than Pap smears.

Bowel Cancer Screening

  • Introduced nationwide with fecal immunochemical tests (FIT).

Lung Cancer Screening Insights

  • High burden of lung cancer in New Zealand; screening with low-dose CT can reduce mortality.

  • Studies confirm significant benefits from early detection through screening programs [NLST, NELSON studies].

Conclusion

  • While screening modifies outcomes, it's imperative to weigh benefits against potential harms.

  • Policies must be informed, ethically sound, and practically viable for patient benefit.


Examples of Screening

  1. Newborn Screening

    • Guthrie Test for phenylketonuria (PKU) to prevent mental retardation.

    • Tests for several conditions: amino acid disorders, cystic fibrosis, congenital conditions.

  2. Hearing Tests

    • Screening for significant hearing loss in infants can aid early development.

    • Treatment could include hearing aids or cochlear implants.

  3. Down’s Syndrome Screening

    • Trisomy 21 risk is age-related, diagnosed antenatally or postnatally.

    • Screening involves Nuchal Translucency scans and blood tests for biochemical markers.

  4. Breast Cancer Screening

    • Free screening offered to women aged 45-69 years every two years.

    • Mammography is sensitive but can have a high false-positive rate.

  5. Cervical Cancer Screening

    • New NHSP focuses on HPV testing rather than Pap smears.

  6. Bowel Cancer Screening

    • Introduced nationwide with fecal immunochemical tests (FIT).

  7. Lung Cancer Screening Insights

    • High burden of lung cancer in New Zealand; screening with low-dose CT can reduce mortality.

    • Studies confirm significant benefits from early detection through screening programs [NLST, NELSON studies].