Screening for Disease

“The presumptive identification of an unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly. Screening tests sort out apparently well persons who probably have a disease from those who probably do not.”

using two or more screeening tests together among large groups of poeple

screening on a large scale of total population groups regardless of risk status

Screens subset sof the population at high risk for disease

Use of screening tests for detection of conditions unrelated to the patient's chief complaing

• Population or epidemiologic surveys
• -purpose is to gain knowledge regarding the distribution and determinants of diseases in selected populations
• No benefit to the participant is implied

• Immediate Objective: identify people as likely or unlikely to have disease
• Long Term Objective: reduce mortality and morbidity in a population

• Prevents disease from occurring
• Goal is to reduce incidence

• Delays onset of and duration of clinical disease
• Goal is to improve survival

• Delays onset of and duration of clinical disease
• Goal is to improve survival

• Slows disease progression; reduces sequelae
• Goal is to improve survival

• Primary: Intervention programs that reduce risky behaviors such as needle sharing and unsafe sex
• Secondary: Screening
• Tertiary: use of drugs to prevent opportunistic infections (immunosuppressed)

• Disease is serious with severe consequences
• Treatment is more effective at an earlier stage
• Disease has a detectable preclinical phase (DPCP)
• DPCP is fairly long and prevalent in the target population

• Severe disease with very dire consequences
• Many tretments reduce disease sequelae when giving early
• Long and highly prevalent DPCP

• Ability of a test to distinguish between who has disease and who does not
• Measured by sensitvity and specificty

Ability of a test to identify correctly those who HAVE the disease

Ability of a test to identify correctly those who DO NOT have the disease

# individuals with disease who test positive / # individuals with disease X 100

# individuals without disease who test negative / # indviduals without disease X 100

• Sensitivity (EX= 80.0%): 80% of people with the disease test positive for the disease
• Specifity (EX= 88.9%): 88.9% without the disease test negative for the disease

Proportion of patientes T+ for the disease who actually have the disease

Porportion of patients T- for the disease who DO NOT have the disease

• High PVP is essential for a successful screening program
• Program detects a large proportion of actual cases among T+
• Low PVEP implies resources are wasted on invasive, expensive diagnostic and follow-ups

Screening tends to identify cases with long preclincal course, less aggressive forms of disease

• Overall goal of screening program is to improve survival
• Se, SP, PVP, PVN are measurable characteristics of a screening test and screening program
• PVP is dependent on prevalence and Sp