My first step would be to confirm that the answer itself charts on the patient report. If a value charts, it would be found in the HL7 outbound message, and might qualify for a LOINC code. If it doesn’t chart, there is no HL7 inclusion, and no LOINC code is needed.
50957-0 Manual Differential Performed Bld is a modeling example, but the specimen type is wrong. The Ordinal scale would be looking for a yes/no format of an answer. The component name does take the standpoint of after the fact (past tense). Another drawback is that it’s only for manual differentials. Would there be a possibility that the fluid is run through a machine for the differential?
If your result field does chart, you may want to consider making a submission like 50957-0, with substitution on specimen at the least.