This SNOMED-valueset ( https://hl7.eu/fhir/laboratory/0.1.0-ballot/StructureDefinition-specimen-additive-substance-eu-lab.html  ) with only 19 values might be too much limited.
SNOMED CT
1259913003    Heparin ammonium
386961008    Aprotinin
29725000    Heparin calcium
21611007    Boric acid
30531001    Calcium oxalate
69519002    Edetic acid
372628006    Edetate
27763000    Hydrochloric acid
414407009    Hirudin
1256100007    Edetate dipotassium
1256101006    Edetate tripotassium
1256102004    Heparin lithium
387418006    Edetate disodium
412546005    Sodium citrate
50045009    Heparin sodium
6910009        Sodium fluoride
50306007    Sodium tetraborate
387168006    Mannitol
115281000146102    Sodium formate

More useful seems to be the valueset  https://terminology.hl7.org/ValueSet-v2-0371.html  (57 concepts), but that has no associated SNOMED codes so far, SNOMED should be asociated before usage.

The bindings should be more open, set from preferred to example.

Kind regards from Franziska van Wüllen and Martina Sender (mio42 GmbH, Germany)