Understand inclusion and exclusion criteria

Start with the purpose of eligibility rules

Inclusion criteria identify characteristics required for the research question. Exclusion criteria identify characteristics that make participation unsuitable under the protocol or interfere with interpretation of the data. NIH describes these criteria (opens in a new tab) as factors used by research teams to decide who can participate.

A criterion can protect safety, define the population, reduce confounding, meet regulatory expectations, or preserve the study’s ability to answer its question. The coordinator and investigator must follow the approved protocol. They cannot waive a rule because a candidate is motivated or lives nearby.

Common inclusion and exclusion criteria

• Condition and treatment history: diagnosis details, disease stage, prior therapies, procedures, and response.
• Medication stability: prohibited drugs, stable-dose periods, washouts, and rescue medication.
• Laboratory and physiological ranges: kidney or liver markers, blood counts, blood pressure, heart rhythm, weight, or other protocol thresholds.
• Timing: recent infection, vaccine, surgery, donation, hospitalization, travel, or participation in another study.
• Reproductive requirements: pregnancy testing, contraception, breastfeeding, sperm or egg donation restrictions, and defined follow-up periods.
• Operational fit: language, device access, shift schedule, distance, visit windows, diary capacity, or caregiver availability when the protocol requires them.

Ask which categories account for the largest share of prescreen failures at that location. Treat the answer as site experience, not a replacement for the protocol.

Distinguish temporary from lasting conflicts

Some criteria use a time window. A recent vaccine, medication course, procedure, donation, infection, or other study may postpone screening instead of ending the possibility. Ask what event starts the clock and what documentation confirms the date.

Do not calculate a medication washout yourself. The protocol, study investigator, and your clinician must guide any medication decision. A washout may carry personal medical risk that a public listing cannot explain.

Understand investigator judgment

Protocols can include objective thresholds and judgment-based criteria such as any condition that could increase risk, reduce adherence, or confound results. Ask who applies that judgment and whether the reason for a screen failure can be shared.

Do not assume a screen failure diagnoses a health problem. Protocol ranges can differ from clinical reference ranges, and research-only assays may not be validated for clinical use. Ask whether a finding requires clinical follow-up and how to obtain a result for your clinician.

What to ask if you do not qualify

Ask whether the decision is final, whether a missing record can resolve it, whether the criterion is temporary, and whether another cohort or study differs. Correct factual errors with documentation. Avoid pressuring staff to reinterpret a safety rule.

Confirm accrued screening payment and reimbursement. Ask what information and specimens will be retained, whether optional future use can be declined, and whether any follow-up is requested.