When is ad-hoc (ad hoc, meaning as needed or without a regular schedule) screening recommended for patients?

Ad-Hoc Screening Is Generally Not Recommended

Ad-hoc screening—meaning opportunistic, unscheduled, or individual-basis screening outside of structured programs—is explicitly discouraged across multiple clinical contexts and should be avoided in favor of organized, evidence-based screening programs with quality control mechanisms. 1

Key Principle: Structured Programs Over Individual Requests

The clearest guidance comes from lung cancer screening, where LDCT screening should not be offered on an ad hoc individual basis, but patients requesting screening should be referred to a dedicated programme with quality control, experienced centers, high-volume thoracic oncology activity, and multidisciplinary management. 1 This principle reflects a fundamental tenet: screening initiated by healthcare providers carries different ethical obligations than responding to symptomatic patients seeking care. 2

When Ad-Hoc Screening May Be Considered

Pre-Procedure COVID-19 Testing

Ad-hoc screening may be appropriate in specific procedural contexts:

• During periods of high community transmission, pre-procedure SARS-CoV-2 testing may be considered for asymptomatic patients undergoing major surgery, though this is not routine screening. 1
• Testing may also be considered before solid-organ transplantation, hematopoietic stem cell transplantation, or CAR T-cell therapy. 1
• The decision must balance patient risk from delaying the procedure against transmission risk, considering vaccination status, PPE availability, and whether the procedure generates aerosols. 1

Symptom-Triggered Evaluation (Not True Screening)

Several guidelines distinguish between screening asymptomatic patients and evaluating those with signs or symptoms:

• Routine screening for coronary artery disease in asymptomatic diabetic patients is not recommended, but cardiac testing is appropriate for those with typical/atypical cardiac symptoms or abnormal resting ECG. 1
• In sickle cell disease, routine screening echocardiography is not recommended for asymptomatic patients, but a targeted history for cardiopulmonary symptoms should prompt diagnostic evaluation. 1
• For heart failure in diabetes, measure BNP or NT-proBNP in those with signs or symptoms; echocardiography follows if levels are abnormal. 1

Why Ad-Hoc Screening Is Problematic

Ethical and Practical Concerns

• Screening initiated by providers requires conclusive evidence that it alters natural history in a significant proportion of those screened—a higher standard than treating symptomatic patients. 2
• Ad-hoc screening lacks the quality control, standardized protocols, and outcome tracking of organized programs. 1
• False-positive results lead to unnecessary anxiety, costs, and risks from additional procedures. 3, 4, 5
• False-negative results create false reassurance and delayed diagnosis when symptoms develop. 4, 6

Resource Implications

• Unproven screening programs divert resources from diagnosing and treating symptomatic patients. 4
• In low-prevalence settings, even highly accurate tests have poor positive predictive value, generating more harm than benefit. 6

Age-Appropriate Scheduled Screening (Not Ad-Hoc)

For context, evidence-based screening follows specific age-based schedules:

• Colorectal cancer screening begins at age 45 for average-risk adults (colonoscopy every 10 years, annual FIT, or CT colonography every 5 years). 7, 8, 9
• Mammography annually starting at age 40 for average-risk women. 9
• Abdominal aortic aneurysm screening is one-time ultrasonography for men aged 65-75 who have ever smoked. 1
• Cardiovascular risk assessment (blood pressure, lipids) annually for adults aged 40-49. 8, 9

Common Pitfalls to Avoid

• Do not order screening tests simply because a patient requests them—refer to structured programs when appropriate screening criteria are met. 1
• Do not perform routine comprehensive metabolic panels or CBCs without clinical indication in asymptomatic patients, as this leads to false positives and unnecessary follow-up. 8, 9
• Do not screen asymptomatic high-risk patients for coronary disease—they should already receive intensive medical therapy, which provides similar benefit to invasive revascularization. 1
• Recognize that earlier diagnosis does not always mean better outcomes—lead-time and length biases can create the illusion of benefit without actual mortality reduction. 5, 6