blood mineral amount blood sodium amount The proportion, quantity, or volume in whole blood, serum, or plasma of this metallic element, the most plentiful extracellular ion in the body and the principal determinant of extracellular fluid volume. CMO:0000060 circulating sodium level Trait.ontology EFO:0009282 blood sodium level CMO:0000499 CMO:0000500 VT:0001776 blood electrolyte amount