Anion gap
A measurement of the interval between the sum of 'routinely measured' cations minus the sum of the 'routinely measured' anions in the blood.
The anion gap = (Na+ + K+) - (Cl- + HCO3-) where Na- is sodium, K+ is potassium, Cl- is chloride, and HCO3- is bicarbonate.
The anion gap can be normal, high, or low.
A high anion gap indicated metabolic acidosis, the increased acidity of the blood due to metabolic processes.
A low anion gap is relatively rare but may occur from the presence of abnormal positively charged proteins, as in multiple myeloma.