6.2: Screening
- Page ID
- 302490
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Screening for a disease simply means testing asymptomatic individuals. The goal of screening for a disease is to detect its presence at an early stage, when treatment can yield a favorable prognosis. Over time, screening has reduced disability or deaths. It is important to note that screening is not a perfect tool; for example, screening data shows that it reduces a person's risk of dying of cancer by 30% to 60%, but they don't eliminate it (National Center for Biotechnology Information, 2025).
There are four criteria for a successful screening program (Riegelman & Kirkwood, 2025):
- The disease produces substantial death or disability: certain diseases, such as cancer and heart diseases, are well-known for being the cause of disability and death in the population. There are other diseases, such as those in childhood, that can cause just as much impairment and disability.
- Early detection is possible and improves outcomes: there are instances in which screening is available, but treatment is not. An example is screening smokers with a lung X-ray. By the time cancer is able to be seen in an X-ray, it is already it is too late for treatment.
- Feasible testing for screening: the requirement for this criterion is to (1) identify the high-risk population, and to (2) be able to test for false positives (test positives, but in reality do not have the disease) and false negatives (test negative for the disease, but in reality have the disease). The goal is to identify the true positives. The most common strategy used is sequential testing, which simply means that after a positive screening test, a diagnostic test follows.
- The patient accepts the possible harms and costs of the screening test: in many instances, the initial screening, such as blood tests, is harmless. However, if the initial tests require a more invasive and costly follow-up (such as surgery), will the patient still agree to the procedure?
When screening tests take place, it is important to notice that:
- One positive screening test is not usually sufficient to diagnose a disease
- Changes within the range of normal can be due to a disease
- The range of normal is not the same for all groups or populations.
Interestingly, Birbeck (2020) offered three main ways population screening can be successful: (1) patients can directly benefit, (2) early diagnosis must be associated with better outcomes, and (3) the cost and risks must not outweigh the benefits. An example of a screening program that did not work was Indiana's mandatory HIV screening for a marriage license in 1994. Within a year of the program's start, many residents were driving across state lines for their marriage licenses. People were inconvenienced, the state lost revenue, and there was little benefit. Records show premarital blood tests were repealed by 2019 (McMaken, 2019).
Let's take the example of colon cancer:
Colon cancer has a high mortality and morbidity and is the second most common cause of death from cancer in both females and males. Early detection (before symptoms arise) improves outcome. Screening for colon cancer has been approved by insurance companies, and patients are frequently undergoing tests (sigmoidoscopy and fecal occult blood testing). This is because the screening is acceptable with respect to costs, harms, and patient acceptance (Riegelman & Kirdwood, 2025).
Reference
Birbeck, G. L. (2000). The benefit of screening must outweigh the risks and costs. The Western Journal of Medicine. May;172(5):308-9. doi: 10.1136/ewjm.172.5.308
McMaken, R. (2019). The pre-marriage blood test in America is now gone. MisesInstitute www.mises.org
National Center for Biotechnology Information. (2025). Screening: Learn more -advantages and disadvantages of screening tests. Institute for Quality and Efficiency in Health Care (IQWiG) https://www.ncbi.nlm.nih.gov/books/NBK611896/
Riegelman, R. & Kirkwood, B. (2025). Public health 101: Improving community health (4th ed). Jones & Bartlett Learning, LLC.