Continuing Education Activity

A health screening test is a medical test or procedure performed on members of an asymptomatic population or population subgroup to assess their likelihood of having a particular disease. Health professionals often think of screening for early diagnosis of cancer (such as Pap smears for cervical cancer or colonoscopy for colon cancer), but there are many other screening tests commonly used, for example, thyroid-stimulating hormone (TSH) for congenital hypothyroidism in newborns, cholesterol level for heart disease, urine drug screen for illicit drug use, or blood pressure for hypertension. Some screening tests are applied to a large segment of the population (for instance, all adults older than age 50), while others target a smaller subset of the population (pregnant women). Many screening tests are widely used in the United States. This activity provides guidelines on the current screening tests and the role of the interprofessional team in patient education on the benefits of screening.

Objectives:

• Identify the function of screening tests.
• Describe the issues of concern with screening test.
• Explain the benefits of screening tests.
• Outline interprofessional team strategies for improving care coordination and communication to advance approved screening tests and improve outcomes.

Introduction

A health screening test is a medical test or procedure performed on members of an asymptomatic population or subgroup to assess their risk of developing a particular disease. We often think of screening for early diagnosis of cancer (such as Pap smears for cervical cancer or colonoscopy for colon cancer), but there are many other screening tests commonly used, for example, thyroid-stimulating hormone (TSH) for congenital hypothyroidism in newborns, cholesterol level for heart disease, urine drug screen for illicit drug use, or blood pressure for hypertension. Some screening tests are applied to a large segment of the population (eg, all adults older than 50), whereas others target a smaller subset (eg, pregnant women). Many screening tests are widely used in the United States. Healthcare providers can agree that early diagnosis of a life-threatening disease for which effective treatment is available is a positive step.

Unfortunately, health screening is complicated. Many articles on screening present a bewildering array of medical economics and biostatistics to make their points, and numerous credible organizations have offered their own (often differing) screening recommendations. The economic implications of screening are real. Even a single screening test applied to a large number (millions) of people can result in billions of dollars in annual health care expenditure. There are legitimate debates about sensitivity and specificity, disease prevalence, predictive values, lead-time bias, screening intervals, and appropriate cutoffs for positive or negative results. Recently, "shared decision making" has been suggested as an option when there is uncertainty about the advisability of a particular screening test (such as the prostate-specific antigen, or PSA, for the early diagnosis of prostate cancer). That may be possible if your patient is an educated professional. However, asking a patient without medical training to understand issues that challenge the intellect and judgment of most trained clinicians does not seem realistic. That the issue arises underscores the urgent need for improved screening tests.[1][2][3][4][5][6]

Function

The function of health screening is to assess the likelihood that an asymptomatic individual has a particular disease, to prevent illness or death from that disease. There are several characteristics of a good screening test.

1. Diseases that are good candidates for screening are those that are prevalent in the population and cause significant morbidity and mortality. In the United States, heart disease and lung cancer are good examples. In contrast, trypanosomiasis may be a suitable target for screening in Tanzania but not in the United States.  
2. The disease must have an asymptomatic period during which treatment reduces morbidity and mortality significantly more than waiting until symptoms develop. Congenital hypothyroidism and cervical cancer are good examples. In contrast, chest x-rays as a screening test for lung cancer were discontinued because of failure to demonstrate the value of early diagnosis.
3. The screening test should have the highest possible sensitivity (few false-negative results) and specificity (few false-positive results). The ideal screening test would be 100% sensitive and 100% specific, identifying all patients with the disease and none without the disease. Unfortunately, no ideal test exists. For example, PSA screening for prostate cancer has a very high false-positive rate, as well as the very real possibility of diagnosing an indolent disease that may never cause symptoms.
4. The screening test should also be inexpensive, readily available, safe, and easy. Many current screening tests are suboptimal. Ask anyone who has had a colonoscopy for colon cancer screening or a low-dose helical computed tomography scan for lung cancer screening. These tests are expensive, inconvenient, and not universally available.
5. Effective treatment for the disease in question should be available at a reasonable cost. Why screen for a disease for which there is no real treatment? 

Issues of Concern

There is no such thing as a perfect screening test. However, comparing a poorly justified screening test with a well-designed test helps clarify what makes screening rational—or wasteful.

Consider first a questionable screening test. Many healthy adults undergo periodic complete blood counts (CBCs) and comprehensive metabolic panels (CMPs) as part of routine care, to identify asymptomatic disease such as anemia or electrolyte abnormalities. Is there scientific evidence supporting this practice in healthy, asymptomatic adults? No. There is none. In this context, such testing is essentially a shot in the dark.

This is not the same as ordering a CBC in a patient with menorrhagia, or monitoring serum chemistries in a patient with hypertension or renal disease. In those cases, testing is targeted and hypothesis-driven. By contrast, routine CBCs or CMPs in healthy, asymptomatic adults are not helpful, reasonable, or cost-effective. Despite this lack of evidence, these tests are commonly ordered.

One explanation is medicolegal anxiety. Clinicians may feel they are more likely to be criticized or sued for doing too little rather than too much, and therefore err on the side of overtesting. Some may further rationalize the practice by noting that, at least, they are not ordering more invasive tests, such as whole-body computed tomography scans. However, when multiplied across thousands or millions of patients each year, even “small” unnecessary tests consume substantial resources. Reducing low-value testing could free funding for thousands or millions of evidence-based screening interventions.

Now contrast this with a reasonable screening test. Determining a woman’s blood type early in pregnancy has been standard of care in the United States since the 1970s. The primary purpose is to identify women with Rh-negative blood type. This screening matters because, when Rh incompatibility is present, timely antenatal and postnatal administration of Rho(D) immune globulin (RhoGAM) dramatically reduces the risk of hemolytic disease of the fetus or newborn.

The underlying problem arises when an Rh-negative mother carries an Rh-positive fetus; without treatment, complications—primarily affecting the fetus or newborn—can worsen with subsequent pregnancies. Because blood typing in pregnancy is nearly universal and RhoGAM is routinely administered when indicated, most younger physicians in the United States have never encountered severe hemolytic disease related to Rh incompatibility.

This example illustrates the characteristics of effective screening: a simple, inexpensive, and widely available test applied to an appropriate population, paired with an effective intervention that meaningfully alters outcomes. When these elements align, screening can virtually eliminate what was once a common and potentially fatal condition.[7][8][9]     

Clinical Significance

A good screening test should target diseases that are prevalent in the population and cause significant morbidity and mortality. The leading cause of death in the United States is heart disease. The second leading cause of death is cancer, with lung cancer and colorectal cancer accounting for the highest number of cancer deaths. The following screening tests are available for these 3 diseases.

Heart Disease

Heart disease in this context refers to ischemic heart disease, also known as coronary artery disease, rather than valvular heart disease or hypertrophic cardiomyopathy. Early identification is possible even during asymptomatic stages through appropriate risk assessment and screening.

Clinicians can identify individuals at increased risk by evaluating established risk factors, including smoking status and family history of heart disease. Periodic assessment of blood pressure, lipid levels (total cholesterol, LDL, and HDL), and blood glucose to screen for diabetes further supports early detection. However, the optimal timing for initiating these evaluations and the appropriate screening intervals are not clearly defined and should be individualized based on patient risk.

There are a variety of heart disease risk-assessment tools, none of which are superior to the others. Subsequently, screening tools became increasingly controversial among healthcare professionals. For example, the value of high-sensitivity C-reactive protein (hs-CRP), resting EKG, exercise stress testing (with or without nuclear imaging), coronary artery calcium (CAC) score determined by electron-beam or multidetector-row computed tomography (EBCT or MBCT), and computed tomography angiography remains to be determined. They are not recommended for an asymptomatic low or average-risk individual. Their role in screening asymptomatic high-risk individuals is less clear, and there is no consistent recommendation for their use. Doctors should get a complete history, a blood pressure reading, a lipid profile, and a fasting blood sugar as screening tests, not for heart disease itself, but to determine the risk factors for heart disease.[10][11]

Lung Cancer  

As we noted above, previous recommendations for screening chest x-rays for the early diagnosis of lung cancer were stopped. While lung cancer could be diagnosed earlier by a screening chest x-ray in an asymptomatic individual, it became clear that early diagnosis did not change the course of the disease. This is an example of lead-time bias. Patients may seem to live longer, but only because the cancer is diagnosed earlier. Other tests, such as sputum cytology, are not beneficial. The most promising test currently under study is low-dose helical computed tomography (LDCT) performed with a maximum inspiratory breath-hold, in 25 seconds or less, with high-resolution reconstruction. There is evidence of a mortality benefit from LDCT, but more studies are needed. Candidates for annual screening are patients aged 55 to 74 (some recommend up to age 80) years, a history of smoking at least 30 pack-years, and, if a former smoker, had quit within the previous 15 years. For former smokers, annual screening should continue until 15 years have elapsed from the date of smoking cessation. Other screening tests currently under study include PET imaging and the identification of molecular and protein-based tumor biomarkers in sputum specimens. There is insufficient evidence to recommend these tests at this time.[12][13][14]

Colorectal Cancer

Both the incidence and the mortality rates from colorectal cancer have been decreasing in the United States for many years, partly (although not exclusively) because of increased screening. There are 2 general groups of screening tests available. Stool-based tests include the guaiac-based fecal occult blood test (gFOBT), the fecal immunochemical test (FIT), and the FIT-DNA test. Endoscopic and radiologic tests include flexible sigmoidoscopy, colonoscopy, and computed tomography colonography (CTC). These tests vary as to cost, ease, sensitivity, and specificity. None of these tests is superior in head-to-head trials; therefore, they are all considered viable options for colorectal cancer screening. Until 1 screening test is shown to outperform the others, any screening test is preferable to none. Tests such as digital rectal exams and air-contrast barium enema are no longer widely recommended for colorectal cancer screening.[4][5]

Other Issues

It is incumbent on clinicians to recommend screening tests with strong evidence supporting their use, not to recommend those without such evidence, and to remain familiar with additional information about specific screening tests as it becomes available. Fortunately, many organizations make and frequently update screening recommendations for a broad range of diseases. Both the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) offer broad screening recommendations that consider, in detail, the pros and cons of various screening tests. Recommendations for a narrower range of screening tests come from organizations such as the American Cancer Society, the American Academy of Pediatrics, and the American Heart Association, among others.[1][4][6][12][15][16]

Enhancing Healthcare Team Outcomes

Healthcare workers should not order screening tests for which there is insufficient evidence or that are very rare. This only leads to higher healthcare costs and subjects patients to unnecessary tests and procedures. It is important to discuss the merits of a screening test with the healthcare team before ordering it. Both the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) offer broad screening recommendations that consider, in detail, the pros and cons of various screening tests. If there is a doubt about a screening test, consultation from a specialist should be sought. Only through open communication among clinicians can screening tests be used appropriately and reduce healthcare costs.

Nursing, Allied Health, and Interprofessional Team Interventions

Nurse practitioners should be familiar with disorders that can be screened for. In general, screening for rare disorders is a waste of time and is associated with higher healthcare costs. It is important to consult with a specialist before ordering a screening test. Most screening tests have not met expectations.

Nursing, Allied Health, and Interprofessional Team Monitoring

When nurse practitioners do order a screening test, it is important to follow up. A common form of malpractice is ordering a test without following up on the result.

Review Questions

• Access free multiple choice questions on this topic.
• Comment on this article.

References

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Disclosure: Donald Givler declares no relevant financial relationships with ineligible companies.

Disclosure: Amy Givler declares no relevant financial relationships with ineligible companies.