The "real-life" variability of CA-125 in ovarian cancer patients

The serum CA-125 antigen value has proven to be useful in predicting changes that affect prognosis and management of ovarian cancer; however, interpreting variations in the tumor marker is still not well-defined. Our goal was to further understand the analytical variability of CA-125 in a conventional hospital laboratory.

In an IRB-approved study, ovarian and primary peritoneal cancer patients receiving active therapy at the Cleveland Clinic Foundation had a blood sample obtained prospectively during a routine clinic visit. The sample was separated into three aliquots then submitted on three different weekdays for CA-125 analysis. Laboratory personnel performing the CA-125 assays had no knowledge that this blood was part of a research study. The CA-125 assay used was a microparticle enzyme immunoassay from Abbott AxSYM system.

Fifty-one blood samples were obtained from 45 patients (median age: 62; range: 45-89). The samples were stratified into 3 sub-groups: <100 U/ml (24 samples), 100-600 U/ml (15 samples), and >600 U/ml (12 samples). Analysis of CA-125 consisted of calculating the standard deviations (SD) and coefficients of variations (CV) for each patient's samples. The median SD for CA-125 <100 U/ml was 0.58, mean SD 1.14 +/- 2.44, median CV 1.49, and mean CV 2.93 +/- 4.43. The median SD for CA-125 100-600 U/ml was 4.51, mean SD 9.93 +/- 11.03, median CV 2.51, and mean CV 7.66 +/- 11.13. The median SD for CA-125 >600 U/ml was 56.12, mean SD 149.73 +/- 230.35, median CV 2.10, and mean CV 10.93 +/- 24.75.

CA-125 assay imprecision can contribute considerably to result variations in a conventional laboratory setting, with the degree of variation being directly related to the absolute CA-125 value. However, the relative variability is fairly constant with a median of 1.5-2.5% of the CA-125 concentration.