Proposed Wording: Remove this extension, use Observation.method or pre-coordinated LOINC code to specify whether LDL was "calculated" .

Comment:

The LDL is calculated boolean extension is not necessary to specify that LDL was calculated (versus measured presumably). This could have accomplished by selecting a pre-coordinated LOINC or by using the Observation.method. Many observations may be either measured directly or calculated or derived from other information. LDL is not unique in that regard and therefore this approach may lead to explosion of extensions used to distingui measured vs. calculated observations and diminish interoperability. We already have Obsevation.method qualifier attribute for the generic purpose of specifying the method if its not already part of the Observation.code.

If LOINC is already used, implementers could simply set Observation.code to 13457-7 LOINC codef or 'Cholesterol in LDL [Mass/volume] in Serum or Plasma by calculation'.

Summary:

Boolean "LDL is calculated" extension to Observation is not needed.