FHIR HAPI Validation for Combination of Elements-CodePudding

I have custom Structure Definition based on Observation resource. Using HAPI for the validation. Is there a way to validate the value combination?

Ex:

"code": {
        "coding": [
            {
                "system": "http://loinc.org",
                "code": "76536-2",
                "display": "Mean Arterial Pressure, Cuff"
            }
        ]
    },

When this one is used, the unit of measure from the valueQuantity should have only corresponding values, not anything from the code valueset for unitofmeasure.

    "valueQuantity": {
      "value": 90,
      "unit": "mm Hg",
      "system": "http://unitsofmeasure.org",
      "code": "mm[Hg]"
    }

In other words, for Mean Arial Pressure LOINC code, valueQuantity.code should not allow kg, for example.

CodePudding user response：

I'm not a FHIRPath/clinical data expert but I think this should work for you

{
  "resourceType": "StructureDefinition",
  "url": "https://test.com/test",
  "type": "Observation",
  "status": "draft",
  "baseDefinition": "http://hl7.org/fhir/StructureDefinition/Observation",
  "snapshot": {
    "element": [
      {
        "path": "Observation",
        "id": "Observation",
        "min": 0,
        "max": "*",
        "base": {
          "min": 0,
          "max": "*"
        },
        "constraint" : [{
          "severity" : "error",
          "expression": "code.coding.where(system = 'http://loinc.org' and code = '76536-2').exists() implies (value as Quantity).where(code='mm[Hg]' and system='http://unitsofmeasure.org').exists()"
        }]
      }
    ]
  }
}

The first part of the condition determines where you have an Observation with the appropriate code. If so it will require that your value has the right unit.

EDIT: To add some more information about what's going on here.

We are using a FHIRPath constraint to express this more complicated validation rule.

The .where(...) (docs) condition filters down a repeated/single field if it matches the condition, in this case that's the code/system combination that matches in LOINC code you care about.

.exists() (docs) returns true if the collection is non-empty.

implies (docs) evaluates the right-hand side condition only if the left-hand side is true.

And finally the (... as Quantity) operator (docs) is used to convert the value[x] field to a specific type, so more operations can be done on it.