ABSTRACT
OBJECTIVE: The use of tumour markers in diagnosis and monitoring is very common. Tumour marker results vary - preanalytical sources of variation, total random analytical error (CV(a)), and within-subject (intraindividual) normal biological variation. There are not so many studies evaluating the biological variations and reference change values (RCV) of these parameters. The aim of our study was to assess: (i) the average inherent intra- and inter-individual biological variation (CV(i) and CV(g)) for CA 19-9, CEA, AFP in a group of healthy individuals; (ii) the significance of changes in serial results of each marker; and (iii) the index of individuality. MATERIAL AND METHODS: The study group comprised 49 healthy volunteers ranging in age between 18 and 60 years (25 M and 24 F). Four blood samples were obtained from each subject; one at each 14-day interval. Each sample from one individual was assayed in duplicate. CA 19-9, CEA, AFP levels were measured by an immunoluminometric assay on a random-access analyser (Architect i2000; Abbott Diagnostics Division). The intra- (CV(i)) and inter-individual (CV(g)) biological variations were estimated from the data generated. Reference change value (RCV) was calculated. RESULTS: The intra-individual/inter-individual biological variations (CVs) for CA 19-9, CEA, AFP were 27.2/64.24 %, 30.87/37.14 % and 26.67/43.65 %, respectively. The critical differences (RCVs) of CA 19-9, CEA, AFP were 64.71 %, 72.57 % and 62.62 %, respectively (Z = 1.65 for unidirectional changes; p<0.05). CONCLUSIONS: Intra-individual biological variation contributes to the variation in serial results and should therefore be included in the criteria for serum tumour marker assessment.
