 As the SIG is calculated from all known charged components of blood, it is considered the gold standard for the quantification of unmeasured anions. In contrast, the traditional anion gap calculation only factors in sodium, potassium, chloride and bicarbonate. In healthy humans, the SIG equals zero. In critically ill patients, a high SIG, defined as 2mEqL, indicates the accumulation of unmeasured anions in blood as a cause of acidosis. The unmeasured anions include lactate, ketoacids, uraemic acids and toxins like ethylene glycol and methanol. Studies found that a higher SIG on admission to intensive care unit is associated with poorer outcomes, and has a role in prediction of outcome in septic patients. However this finding is not consistent. 