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Evaluation of CisBio ELISA for Chromogranin A Measurement
Maili Lim1, Patrick Erdman2, Sun Cho2
1University of North Carolina School of Medicine, Chapel Hill, North Carolina, USA.
Background:
Chromogranin A (CgA) is a nonspecific marker for the presence of neuroendocrine tumors and neuroendocrine differentiation. The objective of this study was to evaluate the performance of the CisBio CgA ELISA.
Methods:
Precision, linearity, limit of blank, and recovery of the CisBio CgA ELISA were evaluated. Seventy waste serum samples obtained from the clinical laboratory at Memorial Sloan Kettering Cancer Center were analyzed by the CisBio CgA ELISA. Results were compared to those obtained from a reference laboratory that used a proprietary ELISA for serum CgA measurement. Paired waste plasma samples were also collected from 24 of these patients to assess possible differences between CgA in serum and plasma. Finally, a preliminary reference range study was performed with samples from healthy volunteers in serum (n = 60) and plasma (n = 60).
Results:
Within-run and between-run precision ranged from 3.0% to 5.1% and 4.8% to 12.9%, respectively. The limit of blank was 2.4 ng/mL. Recovery ranged from 88% to 102%. A statistically significant bias was observed when the CisBio CgA assay results were compared to those of a reference laboratory. Comparison of the 2 assays yielded a slope of 9.05, intercept of -18.0, and a correlation coefficient of 0.955. CgA values in serum correlated well to values measured in plasma.
Conclusions:
The analytical performance of the CisBio CgA ELISA was acceptable. However, CgA results are method-specific owing to lack of standardization and use of different antibodies. This lack of standardization results in several challenges for the clinical laboratory when evaluating a CgA assay.
