Quantities normalization

[niquola]

In the transformation phase, we can precalculate quantity in basic units to be able to compare quantities originally entered in different units. It could be done using UCUM formulas for context-free units and context-dependent algorithms can be applied for specific measurements like Glucose in grams or molls.

Option 1 with $ elements:

valueQuanity:
    value: 97.88
    unit: 'F'
   # calculated
    $value: 36.6
    $unit: 'C'

Option 2 with extension:

valueQuanity:
    extension: [{url: original-quanity, valueQuanityt: {value: 97, unit: 'F'}}]
    value: 36
    unit: 'C'

[niquola]

Another idea is to change the value and unit to normalized and move original to extension:

valueQuanity:
    extension: [{url: original-quanity, valueQuanityt: {value: 97, unit: 'F'}}]
    value: 36
    unit: 'C'

This will allow:

1. to be valid FHIR
2. Do not create extra field if value already in metric system

[gotdan]

I like it! Can we say anything about the metric units in lab results? For example, if a result can be represented as milligrams/deciliter or grams/liter, it would be good to standardize on a unit across results to simplify calculations in queries (while retaining the reported units to display values in the way providers expect).

[niquola]

Potentially we can do even more sophisticated normalizations - like translating Glucose moles into grams, but this will require the knowledge of Observation.code :(

[gotdan]

If the quantity has a ucum system and code, we ought to be able to normalize it though, right?

[johngrimes]

I think normalisation would have to be optional if you want to keep to this principle: #44 (comment)

It should be possible to run transformations on raw data prior to loading it into a database (ETL) or within a database using SQL (ELT)

If you want people to be able to implement the transformation in SQL, that probably precludes the UCUM stuff, which really needs something like https://github.com/FHIR/Ucum-java.