Electrolytes of breast-cyst fluid.

We constructed an electrolyte balance sheet for 11 individual specimens and two pooled specimens of breast-cyst fluid. Na+ and K+ ranged in concentrations from those representative of extracellular fluids (147 and 9 mmol/L, respectively) to those of intracellular fluid or a high K+ secretion (23 and 168 mmol/L, respectively). Cl- concentrations ranged from 9 to 98 mmol/L (mean, 31), bicarbonate concentrations from 0 to 34 mmol/L (mean, 16). Ca2+ concentrations did not exceed 2.1 mmol/L. Total protein ranged from 14.7 to 35.8 gL. Fluid osmolality ranged from 249 to 300 mOsm/kg of water (mean, 280). The difference between measured cations and anions indicates an "anion gap" of 140 mmol/L, which must be carried by 46 mOsm/kg of water. We suggest that tricarboxylic acids of the Krebs cycle may account for the missing trivalent anions.