How to Read Clinical Trial Eligibility Criteria

You have found a clinical trial that looks promising, but the eligibility section reads like it was written for doctors. Terms like "ECOG performance status," "adequate hepatic function," and "no prior systemic therapy" can make your eyes glaze over. This guide breaks down the most common eligibility language so you can quickly tell whether a trial might be a fit, before you even call the research team.

Inclusion criteria vs. exclusion criteria

Every clinical trial lists two sets of requirements. Inclusion criteria describe the characteristics you must have to join. Exclusion criteria describe characteristics that would prevent you from participating.

Think of inclusion criteria as a checklist of "must-haves." For example, a trial studying a new breast cancer treatment might require that participants have been diagnosed with Stage II or III breast cancer. If you have Stage I, you would not meet that criterion.

Exclusion criteria exist primarily to protect your safety. A trial might exclude people with severe kidney disease because the study drug is processed by the kidneys. It might exclude people currently taking blood thinners because of a risk of dangerous interactions.

Meeting every single inclusion criterion and none of the exclusion criteria does not guarantee enrollment. The research team will still conduct screening tests to confirm your eligibility and ensure the trial is appropriate for your situation.

Age and sex requirements

Most trials specify an age range. You will often see something like "18 years and older" or "18 to 75 years." The lower limit is usually 18 because most trials study adult treatments. Pediatric trials are conducted separately with additional safeguards for children.

Some trials are restricted by sex. A prostate cancer trial will enroll males only. A cervical cancer trial will enroll females only. Many trials list "All" for sex, meaning anyone who meets the other criteria can participate regardless of gender.

If a trial lists an upper age limit, it is typically because the study drug has not been tested in older adults, or because the condition being studied primarily affects a younger population. Age limits are not arbitrary: they reflect what the researchers can safely study at this stage.

What "healthy volunteer" means

Some trials, particularly Phase 1 safety studies, recruit "healthy volunteers." This means participants who do not have the disease being studied. These volunteers help researchers understand how a drug behaves in the body, what doses are safe, and what side effects might occur, before testing it in patients.

Healthy volunteer trials often have strict requirements. You may need to be within a certain weight range, have normal blood pressure, and not be taking any prescription medications. The research team will run screening tests to confirm you are in good health.

If a trial says "No" next to healthy volunteers, it means you need to have the specific condition being studied in order to participate.

Common medical terms decoded

Eligibility criteria are full of medical shorthand. Here are the terms you will encounter most often:

ECOG performance status

The ECOG scale measures how well you can carry out daily activities. It runs from 0 to 5. A score of 0 means you are fully active with no restrictions. A score of 1 means you have some limitations but can still do light work. Most trials require an ECOG score of 0 or 1, meaning you need to be relatively functional day-to-day.

Prior systemic therapy

"Systemic therapy" refers to treatments that travel through your entire body, such as chemotherapy, immunotherapy, or hormone therapy. A trial may say "no more than two prior lines of systemic therapy," which means you cannot have received more than two different rounds of these whole-body treatments. This helps researchers study the drug in patients whose cancer has not been heavily pre-treated.

Washout period

A washout period is the time you must wait after stopping a previous treatment before joining a new trial. This ensures the old drug has cleared your system and will not interfere with the study results. Washout periods typically range from two to four weeks but can be longer for drugs that stay in the body for extended periods.

Life expectancy requirement

Some trials require a "life expectancy of at least 3 months" or similar. This is a clinical estimate, not a precise prediction. It ensures participants are well enough to complete the study and benefit from its results. Your oncologist or specialist can help interpret this in the context of your health.

Understanding lab value requirements

Many trials require blood test results that fall within certain ranges. These tests confirm that your organs are healthy enough to process the study treatment safely.

Adequate hepatic function means your liver is working well enough. This is typically measured by ALT and AST levels (liver enzymes) and bilirubin. The trial might say "AST and ALT ≤ 2.5 × upper limit of normal (ULN)," meaning your liver enzymes should be no more than two and a half times the lab's normal range.

Adequate renal function means your kidneys are working properly. This is usually measured by creatinine clearance (CrCl) or estimated glomerular filtration rate (eGFR). A common requirement is "CrCl ≥ 60 mL/min."

Adequate hematologic function relates to your blood counts. Trials often require a minimum hemoglobin level (to ensure you are not severely anemic), a minimum platelet count (for safe blood clotting), and a minimum absolute neutrophil count, or ANC (to confirm your immune system can fight infections).

If these values sound confusing, your doctor can pull up your latest blood work and compare it to the trial's requirements within minutes. You do not need to interpret these numbers on your own.

Do not rule yourself out too quickly

Eligibility criteria can seem intimidating, and it is tempting to assume you do not qualify. However, criteria are often written conservatively. The research team may have flexibility on certain points, or your specific situation may fit even if the wording feels ambiguous.

If a trial interests you, contact the research team or discuss it with your doctor. Many people who think they are ineligible find out they actually qualify after a proper screening visit.

Next steps

Now that you know how to read eligibility criteria, you may want to review our guide on what a clinical trial is for broader context. When you are ready to have a conversation with your medical team, our list of questions to ask your doctor about clinical trials will help you prepare.

On TrialFinder, every trial listing translates eligibility criteria into everyday language. Browse trials by condition to see how it works, and reach out to the study team directly if something looks like a match.