Inclusion criteria should identify the patient population for which the treatment is intended. Therefore, the inclusion criteria can be derived from the “intended use” or “indications for use” for the device. A patient may be eligible for a clinical trial because s/he has some specific likelihood of benefiting from the treatment. This has nothing to do with signing informed consent, or having the right sized vessels, or willingness to return for follow-up procedures.
Exclusion criteria are used to circumscribe a more homogeneous population to help reduce variability to make it possible to identify differences between treatments if they are really there, and to help weed out patients who are unlikely to complete the protocol. Therefore, one might exclude patients with concomitant disease which could confound results; or patients of certain age (e.g., to exclude or include pediatric patients); or patients for whom the device is not appropriately sized.
For example, willingness to return for follow-up is necessary for being in a study, but it is not sufficient. The patient must also have the indication for the specific treatment. We don’t stent all patients just because they are willing to return for follow-up, or because they are over 18; they must also have a need for treatment. However, if a patient is unwilling to return, they must be excluded from the study. Or, a patient may have exactly the right indication to be treated with the device under study, but if there is no size of the device that is appropriate for the patient’s anatomy, that patient must be excluded.
In short, if a patient has the indication for the treatment, s/he may be included in the study. If the patient has any of the exclusion criteria, s/he must be excluded from the study. To state it another way, an inclusion criterion is sufficient all by itself for a patient to be treated with the device (i.e., the patient has the condition for which the device is indicated). Conversely, the inverse of the inclusion criterion is sufficient to exclude the patient. In contrast, while an exclusion criterion is sufficient all by itself to exclude a patient from the study, its inverse is not sufficient to include a patient. For example, if subjects under the age of 18 are being excluded from the study, it is not also true that all people over the age of 18 are eligible to be enrolled in the study.