Visits and Observation period - OHDSI/ETL--PulmonaryHypertensionRegistries GitHub Wiki

Typically, two kinds of healthcare encounters are presented in the registry or clinical trial data: study visits and hospitalizations.

Study visits

Study visits form a skeleton of a study. Every patient’s interaction within a study starts with a screening visit and signature of informed consent, and then they may proceed to a Baseline visit and Follow-up visits. Usually, such encounters happen within one day, so we assume the start date of the visit be equal to the end date of the visit unless there are explicit visit dates in the source dataset. In our practice, the concept id 581477 - ‘Office visit’ is a suitable match for an in-person meeting with a healthcare professional. As for type concepts, use the concept ids recommended in the Introduction. It makes sense to populate the preceding_visit_occurrence_id field for study visits since the order of visits is known from the source. Technically, the preceding ids can be populated by a window function either on the source table or the CDM visit_occurrece table.

Hospitalizations

Another critical interaction with the healthcare system for a patient is hospitalization. Sometimes, such information can be scattered over multiple tables of the source dataset. For example, it can be recorded as an outcome of an adverse event in an appropriate table. In terms of the CDM, hospitalizations differ from study visits by concept id (i.e., 9201 - ‘Inpatient visit’). They also usually last more than one day. However, the preceding visit occurrence id field can also be populated the same way as for study visits - referencing preceding hospitalization or being left unpopulated.

Observation period

When it comes to defining the patient's observation period, it makes sense to consider it his or her time enrolled in the study. So, we can choose a start date as either a date of informed consent signed or the actual enrollment date if it is available. The end date of the observation period would be a day when a person left the study for some reason, i.e., completion of the study, withdrawal of the consent, death, etc.

As for visits, the type concepts should be chosen according to our previous recommendations.

Not all the events will be inside the observation period. A bold example is a medical history, when a patient is being asked at the Baseline visit about their previous conditions, hospitalizations, medications taken, procedures performed, etc. So, medical history records will be translated into events before the observation period starts.