SERUM TUMOR-MARKERS IN MONITORING PATIENTS - INTERPRETATION OF RESULTS USING ANALYTICAL AND BIOLOGICAL VARIATION

During cancer monitoring, data on biological and analytical variation are required in order to define the critical difference which provides on objective means to interpret serial values. We evaluated four tumo ur markers on serial samples collected from healthy subjects and patie nts. Analytical coefficients of variation (CVA), were obtained from '' precision profiles'' based on the differences between duplicates cumul ated from assay runs in the laboratory. We defined the mean intrasubje ct biological variation (CV1) for CA 19-9 and TPA, separately for heal thy people and patients; since the differences between the two groups were not statistically significant, we pooled the results and re-evalu ated CV1 in the combined groups (CA 19-9; CV1 = 15.9%; TPA; CV1 = 25.7 %). In addition, we evaluated CV1 for CEA (10.9%) and for TPS (25.9%) in patients. We then evaluated the inter-subject biological variations (CVG); the calculated indices of individuality for the four markers w ere less than 0.6 which shows conventional reference values to be of l ittle utility for interpretation. We finally evaluated the critical di fferences (p<0.05) for CA 19-9 (CD = 44.7%), for TPA (CD = 72.5%), CEA (CD = 32.7%) and TPS (CD = 72.5%); these are generally applicable sin ce there was no heterogeneity in intra-subject biological variability.