This is the ValueSet that contains all the codes in LOINC Codes for Serum Potassium (http://hl7.org/fhir/uv/pddi/ValueSet/valueset-magnesium-LOINC) and LOINC Codes for Serum Potassium (http://hl7.org/fhir/uv/pddi/ValueSet/valueset-magnesium-LOINC). E.g. what you have to deal with if you get resources containing codes in either of them