B-028 Absorbance vs. Chemiluminescent: A Comparison of Two Different Enzyme-Immunoassay Methods of Digoxin Measurement

Background Digoxin is a cardiac glycoside which is commonly used for the treatment of congestive heart failure as well as some cardiac arrhythmias. Treatment with digoxin increases intracellular calcium ions and cardiac contraction and slows down the heart rate. Therapeutic range of digoxin is narrow. Excess administration of Digoxin could result in toxicity undistinguishable from original cardiac symptoms. Although the therapeutic and toxic concentration overlaps, measurement of digoxin helps to maintain effective concentration and prevent overdose. Enzyme-immunoassays are widely used to measure the concentration of digoxin. Absorbance and chemiluminescent Enzyme-immunoassays are two common methods used to measure digoxin. This study reports a detailed comparison of these two methods which could assist in choosing a more appropriate one for digoxin measurement. Methods This retrospective study was a part of the validation study of Beckman AU680 and AU5800 chemistry analyzers performed at Albany Medical Center. Absorbance and chemiluminescent Enzyme-immunoassays for digoxin measurement were performed on Beckman AU5800 and AU680 analyzers, respectively. Linearity data was used to determine the average percent recovery. Quantitative method correlation was performed by applying Deming, Passing-Bablok, and Regular regression analyses and used to determine the bias with reference method. Comparison of method specifications were based on published literature investigation. Results While both absorbance and chemiluminescence methods are immunoassay-based, they have some differentiating and similar criteria as well. Although they are similarly impacted by endogenous and exogenous interferents, chemiluminescence method have a favorable calibration frequency, analytical measurement range, and reportable range. While mean percent recovery was comparable for both absorbance and chemiluminescence methods, chemiluminescence method displayed a reduced systematic bias and imprecisions as compared to absorbance method. Slopes of Deming and regular regression analyses of chemiluminescence method displayed proportional biases. On the other hand, intercepts of Deming, Passing-Bablok, and regular regression analyses of absorbance method displayed constant biases (Table 1). Statistical analyses were performed by using EP evaluator and GraphPad Prism. Conclusion Given Beckman chemistry analyzers are standardized, difference of immunoassay methods could result in variation of validation specifications. In this study, chemiluminescence immunoassay exhibited lesser bias and imprecision as compared to absorbance immunoassay.