<?xml version=“1.0” encoding=“UTF-8”?> <Observation xmlns=“hl7.org/fhir”>

      <id value="herd1"/>
      <!--    the mandatory status    -->
      <meta>
  <security>
    <system value="http://terminology.hl7.org/CodeSystem/v3-ActReason"/>
    <code value="HTEST"/>
    <display value="test health data"/>
  </security>
</meta>
<status value="final"/>
      <!--   category code is A code that classifies the general type of observation being made. This is used for searching, sorting and display purposes.  -->
      <category>
              <coding>
                      <system value="http://terminology.hl7.org/CodeSystem/observation-category"/>
                      <code value="laboratory"/>
                      <display value="Laboratory"/>
              </coding>
              <text value="Laboratory"/>
      </category>
      <!--   
  Observations are often coded in multiple code systems.
    - LOINC provides codes of varying granularity (though not usefully more specific in this particular case) and more generic LOINCs  can be mapped to more specific codes as shown here
    - snomed provides a clinically relevant code that is usually less granular than LOINC
    - the source system provides its own code, which may be less or more granular than LOINC
   -->
      <code>
              <!--    LOINC - always recommended to have a LOINC code    -->
              <coding>
                      <system value="http://loinc.org"/>
                      <code value="80219-9"/>
                      <!--  more generic methodless LOINC  -->
                      <display value="Mycoplasma hyopneumoniae Ab sample/Positive control in Serum by Immunoassay"/>
              </coding>
              <!--    Also, a local code specific to the source system    -->
              <coding>
                      <system value="http://acme.org/devices/clinical-codes"/>
                      <code value="Mycoplasma"/>
                      <display value="Mycoplasma"/>
              </coding>
              <text value="Mycoplasma hyopneumoniae - MHP"/>
      </code>
      <!--     subject is a herd of 2500 breding sows   -->
      <subject>
              <reference value="Group/herd1"/>
      </subject>
      <encounter>
              <display value="part of a health assurance program"/>
      </encounter>
      <effectiveDateTime value="2017-11-20"/>
      <!--    In FHIR, units may be represented twice. Once in the
  agreed human representation, and once in a coded form.
  Both is best, since it's not always possible to infer
  one from the other in code.

  When a computable unit is provided, UCUM (http://unitsofmeasure.org)
  is always preferred, but it doesn't provide notional units (such as
  "tablet"), etc. For these, something else is required (e.g. SNOMED CT)
    -->
      <valueQuantity>
              <value value="0.2"/>
              <unit value="% (sample/positive control)"/>
              <system value="http://unitsofmeasure.org"/>
              <code value="%"/>
      </valueQuantity>
      <interpretation>
              <coding>
                      <system value="http://terminology.hl7.org/CodeSystem/v3-ObservationInterpretation"/>
                      <code value="NEG"/>
                      <display value="Negative"/>
              </coding>
              <text value="Negative"/>
      </interpretation>
      <!--   Specimen is a pooled serology sample of 30 animals.  -->
      <specimen>
              <reference value="Specimen/pooled-serum"/>
              <display value="30 serum"/>
      </specimen>
      <referenceRange>
              <text value="&gt;0.4 Positive; 0.3 to 0.4 Suspect &lt; 0.3 Negative"/>
      </referenceRange>

</Observation>