When should ad-hoc screening be considered for a patient?

Ad-Hoc Screening: When to Consider

Ad-hoc screening should generally be avoided in favor of organized, evidence-based screening programs with quality control, as ad-hoc individual screening lacks the infrastructure to ensure appropriate patient selection, follow-up, and management of findings. 1, 2

Primary Principle: Organized Programs Over Ad-Hoc Screening

The fundamental distinction between appropriate screening and ad-hoc testing is the presence of a structured program with quality assurance mechanisms. Screening should not be offered on an ad-hoc individual basis; patients requesting screening should instead be referred to a dedicated program with established protocols, multidisciplinary teams, and quality control. 1, 2

Why Ad-Hoc Screening Is Problematic

Ad-hoc screening—testing performed opportunistically without systematic protocols—carries substantial risks that organized programs are designed to mitigate:

• False-positive results lead to unnecessary anxiety, additional diagnostic procedures with associated risks and costs, and potential overtreatment of borderline abnormalities 3, 4, 5
• False-negative results create false reassurance, potentially delaying diagnosis when symptoms subsequently develop 4, 5
• Labeling effects from positive results (even true positives for conditions where intervention benefit is unproven) can negatively impact quality of life 4
• Resource misallocation diverts healthcare resources from symptomatic patients who need diagnosis and treatment 4

When Ad-Hoc Screening May Be Considered

COVID-19 Pre-Procedure Testing

The most clearly defined scenario for ad-hoc screening involves pre-procedure SARS-CoV-2 testing:

• Consider testing during periods of high community transmission before major surgery in asymptomatic individuals, though evidence for poor outcomes in this population is limited 1
• Testing may be considered before solid-organ transplantation, hematopoietic stem cell transplantation, or CAR T-cell therapy 1
• Balance procedural urgency against transmission risk, considering patient vaccination status, whether the procedure generates aerosols, and availability of appropriate PPE 1
• Testing within 72 hours of the procedure is the typical institutional standard, though this represents a compromise between accuracy and logistics 1

Critical caveat: Even in this context, decisions must weigh the risk of delaying necessary procedures against marginal transmission reduction, particularly when appropriate PPE and infection control measures are in place 1

Ventilator Liberation Screening

In the ICU setting, protocolized screening for extubation readiness represents appropriate systematic assessment:

• Use protocolized screening at regular intervals to identify when patients meet prespecified physiologic parameters for extubation readiness testing, rather than relying solely on ad-hoc clinical judgment 1
• This reduces invasive mechanical ventilation duration by several hours to days and may lower extubation failure rates 1

This is not truly "ad-hoc" but rather systematic screening integrated into clinical workflow 1

Screening That Should Never Be Ad-Hoc

Lung Cancer Screening

LDCT lung cancer screening must only be performed within high-quality, high-volume centers with multidisciplinary teams, expertise in LDCT interpretation and lung nodule management, and comprehensive diagnostic and treatment services 2, 6

• Patients aged 50-80 years with ≥20 pack-years smoking history (current smokers or quit within 15 years) qualify for organized screening programs 2
• Ad-hoc individual LDCT screening outside dedicated programs is explicitly not recommended, even when patients request it 1
• The positive predictive value for pulmonary nodules ≥4 mm is only 3.8%, meaning 96.4% of positive results are false-positives, requiring expert management protocols 6

Colorectal Cancer Screening

Screening should follow established protocols with either colonoscopy every 10 years or annual FIT, beginning at age 50 (age 45 for African Americans) 1

• Organized programs with quality control are essential for managing the sequential testing and follow-up required 1
• Ad-hoc screening without systematic follow-up protocols risks incomplete evaluation of positive findings 7

Diabetes Screening

While the evidence for population-based diabetes screening is limited, when screening is performed:

• Target patients with hypertension or hyperlipidemia where the number needed to screen to prevent cardiovascular events is substantially lower than in the general population 1
• Use fasting plasma glucose testing in patients ≥45 years or younger patients with risk factors (family history, overweight, hypertension) 1
• Ad-hoc testing without consideration of pretest probability and follow-up plans for positive results is problematic 1

Essential Requirements When Any Screening Is Considered

Regardless of the clinical context, screening should only proceed when:

1. Compelling evidence exists that screening improves health outcomes (reduces mortality or morbidity) in asymptomatic people 1, 3
2. Test performance is well-characterized in the target population, including sensitivity, specificity, and positive/negative predictive values 1, 5
3. Resources for timely and appropriate follow-up are available, including a knowledgeable clinician workforce 1
4. Net benefit at acceptable cost has been demonstrated, accounting for potential harms 1, 3
5. Patient preferences are respected through shared decision-making with appropriate information about benefits and limitations 1

Common Pitfalls to Avoid

• Do not perform screening tests simply because they are available or because patients request them without evidence of benefit 3, 4
• Do not interpret statistical abnormalities out of clinical context (e.g., borderline lab values in asymptomatic patients) as this leads to unnecessary costs and anxiety 4
• Do not assume earlier diagnosis is always better—lead-time bias and length bias can create the illusion of benefit without actual mortality reduction 8, 5
• Do not screen in low-prevalence populations where even excellent tests have poor positive predictive values, resulting in more harm than benefit 5
• Do not initiate screening without established protocols for managing positive results, as this violates the ethical principle that screening should only be offered with conclusive evidence of effectiveness 7

Algorithmic Approach to Ad-Hoc Screening Requests

When a patient or clinical situation prompts consideration of ad-hoc screening:

1. Determine if organized screening programs exist for the condition in question

   • If yes → Refer to established program rather than performing ad-hoc testing 1, 2
   • If no → Proceed to step 2

2. Assess whether the patient has symptoms suggesting the disease

   • If symptomatic → This is diagnostic testing, not screening; proceed with appropriate workup 1
   • If asymptomatic → Proceed to step 3

3. Evaluate evidence for screening effectiveness in this population

   • Strong evidence of mortality/morbidity reduction → Consider screening within quality-controlled framework 3
   • Insufficient evidence → Do not screen; explain limitations to patient 1

4. Confirm infrastructure for follow-up exists

   • Established protocols for positive results → May proceed 1
   • No clear follow-up pathway → Do not screen 4

5. Engage in shared decision-making with patient about benefits, harms, and alternatives 1