Screening Processes and Types

Screening

• Screening is the process of testing a large group of people to identify individuals with a disease or risk factors, even if they show no symptoms. It's primarily for secondary prevention – early detection and treatment.
• Screening tests don't diagnose a disease; they indicate the presence or absence of a risk factor.
• A screening program aims to find and treat disease early, potentially reducing disease duration and severity.

Types of Screening

• Mass screening: Tests the entire population (or a subset) regardless of risk factors. Examples include visual defects in children and newborn screening in Japan.
• Multiple/Multiphasic screening: Uses multiple tests simultaneously on the same individual. Example screening tests commonly done on the same individual would include: blood sugar, glucose tolerance tests, and blood counts.
• Targeted screening: Focuses on specific high-risk groups. Examples include screening pregnant women for Down syndrome in families with prior cases and screening for HIV/STIs in specific risk groups.
• Case-finding/Opportunistic screening: Tests individuals seeking healthcare for unrelated issues. An example would be RHD screening in children.

Screening Tests

• The screening test itself must be inexpensive, easy to perform, acceptable to the public, reliable, and validated. Validity is determined by the tests’ sensitivity and specificity. The reliability of a test is measured based on consistent results.
• Sensitivity: The ability of a test to correctly identify people with the condition (true positive rate). A high sensitivity implies that the test correctly identifies most people with the disease.
• Specificity: The ability of a test to correctly identify people without the condition (true negative rate). A high specificity implies that the test identifies most people without the disease.
• Predictive values: Positive predictive value (PPV) is the probability of a patient actually having the disease given a positive test. Negative predictive value (NPV) is the probability a patient does not have the disease given a negative test.

Diagnostic Tests

• The aim of diagnostic testing is to confirm diagnoses based on symptoms and signs.
• These tests are usually laboratory-based investigations, including genetic, microbiological, biochemical, or physiological tests.

Screening vs. Diagnosis

• Screening tests are performed on a large, apparently healthy population, looking for unrecognized conditions or risk factors.
• Diagnostic tests are used on individuals with evident symptoms or concerns to confirm diagnoses. They differentiate potential diseases. Screening is about finding potential diseases and diagnosis is for identifying and confirming the exact disease in a patient.

Surveillance

• Surveillance is a systematic process of data collection, analysis, interpretation, and dissemination of health information to inform public health practice. Surveillance is integrated with dissemination of information to those who are in need, timely.
• Its purpose is to monitor trends, predict potential outbreaks or problems, and inform health policies.

Types of Surveillance

• Passive surveillance: Relies on healthcare providers or labs to report disease cases. It's efficient but can have incomplete data due to underreporting.
• Active surveillance: Health departments actively seek out and collect data on specific conditions. It requires more resources but is more comprehensive.
• Sentinel surveillance: Focuses on a specific subgroup of the population to monitor for early signs of disease or health issues. This can help detect trends or potential outbreaks sooner.
• Scanning Surveillance: Targets specific clinical syndromes (signs or symptoms) before a definitive diagnosis is reached. It's helpful when a precise diagnosis isn't available.

Sources of Surveillance Data

• Sources vary depending on the disease and health outcome monitored. Some typical sources or examples include:
• Mortality data (death records)
• Morbidity data (illness records)
• Laboratory data (e.g., lab reports, unusual test results)
• Epidemiology data (population-wide or specific group studies)
• Environmental data.

Uses of Surveillance

• Monitoring disease trends
• Describing the natural history of diseases
• Identifying epidemics or new syndromes
• Monitoring changes in infectious agents
• Identifying areas for research
• Evaluating hypotheses
• Planning public health policies
• Evaluating public health interventions