Background: In our lab, the assay for direct bilirubin using the diazotized colorimetric method is routinely performed using automated analyzer. Previously we used reagents that were prepared in-house. However, results of the quality controls tend to be in the low ends. Therefore, we considered commercially available reagents for the bilirubin assay, however, the available commercial reagents were provided only in small volume package and had a short shelf life, and were thus unsuitable for our laboratory. We then decided to improve our in-house reagents for the test.
Objective: The aim of this work was to modify and improve the existing reagent formulas for
measurement of direct bilirubin which are suitable for routine clinical laboratory testing as well to produce accurate and reproducible results.
Method: The modified in-house reagents were compared to the commercially available reagents by measuring direct bilirubin in 105 serum samples using the Modular P800 Analyzer. The differences between the results from both methods were assessed using paired-t test. The correlation was determined using linear regression analysis.
Results: The modified in-house reagents showed good precision with within-run precision (%CV = 0.77 and 0.55, N=20) and between-run precision (% CV = 2.41 and 2.56) at low and high level respectively. The comparison of the results measured by commercial and modified in-house reagents were 2.22±2.59 and 2.25±2.50 mg/dL respectively. There was no significant difference between the results from two methods (p>0.05), mean difference -0.0285 and high correlation was obtained (r=0.998; y=0.9578x+0.1146).
Conclusion: The modified in-house reagents for direct bilirubin assay provide accurate, precise and reproducible results comparable with those derived from the commercial reagents.