Performance characteristics of an automated assay for the quantitation of CYFRA 21-1 in human serum

Objectives: A fragment of cytokeratin 19, CYFRA 21-1, has been reported to be a sensitive tumor marker for non-small cell lung cancer (NSCLC). We describe analytical performance characteristics of a novel CYFRA 21-1 assay and hypothesize that CYFRA 21-1 complements the clinical sensitivity of carcinoembryonic antigen (CEA) and squamous cell carcinoma antigen (SCCa). Design and methods: Performance characteristics of a CYFRA 21-1 immunochemiluminescent assay included analytical sensitivity, imprecision, linearity, analyte stability, and reference interval determination. Ninety-two pretreatment NSCLC serum samples were tested for CYFRA 21-1, CEA, and SCCa. Sensitivity was determined for each marker individually and in combination, with regard to tumor stage and histology. Results: The analytical sensitivity was 0.01ng/mL. Total imprecision ranged from 4.0 to 6.3% at 4.9 to 28.4ng/mL, respectively. The assay was linear from 0.9 to 71.4ng/mL (slope=0.995, intercept=-0.60, r2=0.999). CYFRA 21-1 was stable for 48h at ambient temperature and 14days at 4°C. The 97.5th percentile of a reference population was 1.9ng/mL. Across disease stage, the sensitivities of CYFRA 21-1, CEA, and SCCa were 17-81%, 30-52%, and 24-39%, respectively. CYFRA 21-1 combined with CEA or SCCa increased sensitivity above that of any single marker. Conclusions: An immunochemiluminescent assay for CYFRA 21-1 had favorable performance characteristics. CYFRA 21-1 was complementary to CEA and SCCa and increased clinical sensitivity in patients with NSCLC. © 2010 The Canadian Society of Clinical Chemists.