Screening Techniques and Types

Screening

• Screening involves testing a large group of people for a disease or risk factors associated with a disease.
• The goal is early detection and intervention.
• Screening tests do not establish a diagnosis, but rather identify the presence or absence of a risk factor. Further follow-up and treatment are required.
• Screening tests are applied to a large, unselected population. Everyone in the group is screened regardless of the probability of having the disease or condition.
• Examples include visual defects in school children, mammography in women over 40, and newborn screening in Japan.

Types of Screening

• Mass screening: Screening the entire population (or a subset) to identify those with a condition. This approach is not specifically for disease prevention but rather focused on those who will benefit from early treatment to reduce illness duration.
• Multiple/Multiphasic screening: Using several tests simultaneously during one screening program. This allows for the diagnosis of multiple conditions quickly.
• Targeted screening: Screening specific groups with particular exposures to detect a condition.
• Case-finding/Opportunistic screening: Screening patients who have already visited a healthcare facility for other reasons.

Screening Tests

• Screening tests must be inexpensive, easy to use, acceptable to the public, reliable, and valid.
• Validity means measuring what the test is intended to measure. Validity is assessed through sensitivity and specificity.
• Reliability means the test provides consistent results.
• Sensitivity is the test's ability to identify a person with a condition as positive.
• Specificity is the test's ability to identify a person without a condition as negative.

Indicators to Evaluate Screening Tests

• Sensitivity: Proportion of those with a condition who test positive.
• Specificity: Proportion of those without a condition who test negative.
• Predictive value: Probability that an abnormal test result indicates an actual condition.

Screening Test Results

• True positives: Sick people correctly diagnosed as sick.
• False positives: Healthy people incorrectly identified as sick.
• True negatives: Healthy people correctly identified as healthy.
• False negatives: Sick people incorrectly identified as healthy.

Diagnostic Tests

• The aim of a diagnostic test is to confirm a possible diagnosis based on the patient's symptoms.
• These tests frequently involve laboratory procedures such as genetic, microbiological, biochemical, or physiological investigations.

Screening vs. Diagnosis

• Screening is performed on a healthy population, while diagnosis focuses on diseased individuals.
• Screening prioritizes high sensitivity for early detection, whereas diagnosis emphasizes high specificity to accurately identify the illness.
• Screening tests are typically less costly and conducted more frequently than diagnostic tests.

Surveillance

• Surveillance involves continuous monitoring, analysis, and interpretation of health data.
• Surveillance is crucial for public health interventions and implementation.
• It is an ongoing, systematic process important for planning, implementation, and evaluation of public health programs.
• Data is used for monitoring disease trends, describing the natural history of diseases, identifying epidemics, monitoring infectious agents, evaluating hypotheses, planning public health policy, and evaluating its effectiveness.

Types of Surveillance

• Passive surveillance: Health departments rely on health care providers or laboratories for reporting.
• Active surveillance: Health departments actively contact providers/labs to collect data.
• Sentinel surveillance: Monitoring key health events or specific subpopulations to identify potential problems.
• Scanning surveillance: Detecting syndromes or early signs of disease before a widespread outbreak.

Sources of Surveillance Data

• Various sources, including mortality and morbidity data, reports from labs, epidemiological investigations, and environmental monitoring.