CA 125 in peritoneal fluid: reliable values at high dilutions.

Forty-three samples of peritoneal fluid from women undergoing laparotomy or laparoscopy for various gynecologic diseases were examined to determine and characterize CA 125 antigen. The data were compared with the corresponding serum levels. CA 125 levels in undiluted peritoneal fluid ranged between 41-301 U/mL and were significantly higher than levels in serum, except in cases of ovarian carcinoma. However, when CA 125 of peritoneal fluid was measured at dilutions greater than 1:50, higher antigen levels were measured (1120-31,500 U/mL), with the highest CA 125 values in patients with ovarian carcinoma. Measurements at dilutions of less than 1:50 were also affected but did not show any decreased binding of the antigen. Immunoblotting analysis of serum and peritoneal fluid indicated the presence of two main bands in each. The monoclonal antibody OC 125 reacted strongly with peritoneal fluid CA 125, in agreement with the CA 125 values obtained by immunoradiometric assay using high dilutions. These data suggest that CA 125 measurements in peritoneal fluid are unreliable unless the samples are diluted 1:50 or more. Furthermore, the statistical difference found between patients with benign and malignant tumors and those with leiomyomata uteri and controls suggests that diluted peritoneal fluid could have a role in identifying abnormal antigen levels.