Screening

Screening is a process of identifying apparently healthy people who may be at increased risk of a disease. By this process, screening positive individuals is placed for more diagnostic tests to rule out the presence of a disease. Even if a screening test is found negative, the apparently “at risk” people are screened for the disease at a subsequent intervals so that the disease can be identified earlier, and the treatment can be initiated before the disease is severe enough. There are specific screening tests targeting a disease, e.g., mammogram for breast cancer and PSA for prostate cancer. This chapter discusses the characteristics of an ideal and effective screening test, such as sensitivity, specificity, predictive values, and accuracy of the screening test with real-life examples. Here, the readers will be familiar with a few other terms such as total preclinical phase, detectable preclinical phase, lead time, validity, reliability, and likelihood ratio. This chapter will also discuss about selecting a suitable cutoff point of between normal and abnormal values of a test and how it affects sensitivity and specificity of the screening test.