Ionic environment of the blood depicted to emphasize the need for charge balance. Ionic environment of the blood depicted to emphasize the need for charge balance. Often referred to as a “gamblegram” on the basis of the work of James L. Gamble, the total circulating cations and total circulating anions are shown. At all times, the sum of both entities must be equal. This equivalency remains the foundation of the derivation of the serum anion gap. Jeffrey A. Kraut, and Nicolaos E. Madias CJASN 2007;2:162-174 ©2007 by American Society of Nephrology