onset[x]Record of the date and/or time of the onset of the reaction caused by the allergy or intolerance which can be recorded in one of five ways;
onsetDateTimeonsetAgeonsetPeriodonsetRangeonsetString.Provider systems are recommended to support at least AllergyIntolerance.onsetDateTime and AllergyIntolerance.onsetAge where this date is available.
It is recommended not to record the onset using an AllergyIntolerance.onsetPeriod or AllergyIntolerance.onsetRange as these data types are complex and less useful. If the exact onset date is not known, but was between two known dates, e.g. 2018 and 2019, then use the lower/older date as the AllergyIntolerance.onsetDateTime instead of using an AllergyIntolerance.onsetPeriod.
It is recommended not to record the onset using an AllergyIntolerance.onsetString as this data will not be machine processable.
Consumer systems SHALL be able to handle any of the AllergyIntolerance.onset data types.