The hyponatremia found in multiple myeloma and which is associated with a reduced anion gap (ag) is considered to be pseudohyponatremia due to the displacement of water by the high globulin content in the blood. Serum proteins participate in acid-base balance. Stewart and other authors in their approach to acid-base interpretation acknowledge electrical neutrality as a fundamental characteristic of body fluids. Furthermore, they have shown that both the strong ion difference (SID) and protein, specifically, negatively-charged albumin affect hydrogen ion concentration (H+) in the body - i.e., for example an increase in SID leads to a decrease in H+ and a decrease in albumin leads to a similar effect. The M proteins of multiple myeloma are positively charged. As a result they cause a decrease in sodium levels and the anion gap and thus a true hyponatremia.