pH as a marker of breast cyst fluid biochemical type.

A previous study reported pH levels in human breast cyst fluid ranging from 7.00 to 7.80 with the cut off between Type I (high K+, low Cl-) and Type II (high Na+, high Cl-) cysts at pH 7.40. Our data indicate a wider range of pH levels in human breast cyst fluids with Type I cysts consistently having acidic levels below pH 7.0 while Type II cysts had pH levels greater than 7.0. Type I acidic cysts characteristically also contain greater amounts of organic acids than Type II cysts. Thus, the pH of breast cyst fluid appears to be related to the electrolyte profile.