Analytical validation of an in-house method for adenosine deaminase determination

Background: The Adenosine Deaminase (ADA) Enzyme is a marker of inflammatory processes whose activity can be measured through a colorimetric method developed as an in-house assay. This validation can reduce costs and expand the alternatives for laboratory diagnosis.

Methods: The ADA analysis was achieved through a modified form of Giusti and Galanti's (1984) method. The following parameters were characterized: calibration curve, linearity, analytical sensitivity, limit of detection, limit of quantification, method working range, precision (within-assay and between-assay), bias, total analytical error, and sample stability. The results were statistically evaluated and compared with quality specifications based on biological variations and the performance of commercial tests.

Results: The analytical sensitivity and limit of detection (0.013 and 3.0 U/L, respectively) were lower than those of commercial tests. The method's working range was 3.2-100.0 U/L. According to the quality specification, the method showed optimum performance with a bias <3.5%. However, repeatability (2.2% and 1.7% for normal- and high-activity samples, respectively) and reproducibility achieved worse results when compared to commercial tests. The method demonstrated an inappropriate between-assay precision for low enzymatic activity (10.4%) and the minimum and desirable performance for medium (8.8%) and high (5.0%) activities, respectively. It also presented at least a minimum performance (<25%) for the total analytical error of the three analyzed samples. The pleural fluid samples were found to be stable at -20°C for six days.

Conclusion: The findings show that the in-house method displays an acceptable performance and is capable of generating results comparable to existing commercial tests.