anion gap serum anion gap 2011-11-02T04:07:40Z CMO:0000569 The serum anion gap is a measurement of the difference-or gap-between the negatively charged and positively charged electrolytes in serum, i.e. blood plasma from which clotting factors have been removed. If the anion gap is either too high or too low, it may be a sign of a disorder in the lungs, kidneys, or other organ systems. clinical_measurement_ontology mshimoyama