The Utility of Screening

The Detectable Pre-Clinical Phase

Without screening, diagnosis of disease only occurs after symptoms develop. However, disease frequently begins long before symptoms occur, and even in the absence of symptoms there may be a point at which the disease could be detected by a screening test. The time interval between possible detection by screening and later detection after symptoms is the "detectable pre-clinical phase" or DPCP. We hope that detection of disease in the DPCP will lead to earlier treatment and that this, in turn, will lead to a better outcome. However, this is not always the case.

When Screening Can Be Beneficial

  1. The disease is serious (e.g., cervical cancer).
  2. When treatment before symptoms occur is more effective than treatment that is delayed until symptoms appear.
  3. When the prevalence of disease in the DPCP is relatively high.

By these criteria, blood pressure screening to detect and treat hypertension is an ideal circumstance for screening.

However,screening is not always appropriate:

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Characteristics of a Good Screening Test

Sources of Unreliability (Inconsistency)

If a test is reliable, it gives consistent results with repeated tests. Variability in the measurement can be the result of physiologic variation or the result of variables related to the method of testing. For example, if one were using a sphygmomanometer to measure blood pressure repeatedly over time in a single individual, the results might vary depending on:

The reliability of all tests can potential be affected by one or more of these factors.