B-022 Performance evaluation of total protein and albumin in body fluids on the Beckman AU platform

Background Spontaneous bacterial peritonitis (SBP), a bacterial infection of ascitic fluid, is a common and potentially fatal complication in cirrhosis with ascites. Determining patients at high risk of SBP, in part, is dependent on total protein and albumin concentrations in ascitic fluid. Currently, the Beckman AU platform can be used to measure total protein and albumin in serum and plasma with a manufacturer-stated lower quantitation limit of 3 g/dL for total protein, and 1.5 g/dL for albumin; however, total protein in ascites at a concentration <1.5 g/dL puts patients at high-risk for development of SBP, and a serum albumin ascites gradient of <1.1 g/dL excludes portal hypertension as a cause of ascites. At the current declared cut-offs of 3 g/dL for total protein, and 1.5 g/dL for albumin, the assays are not useful for testing ascites fluid. To bridge this important gap in diagnostic capacity and prevent further unnecessary testing in patients, we sought to evaluate whether the limit of quantitation was lower than what has been declared and see if it could be expanded on the Beckman AU platform to less than 3 g/dL for total protein, and less than 1.5 g/dL for albumin. Methods Performance of total protein and albumin in peritoneal fluid (diluted in deionized water for lower concentrations) was evaluated on the Beckman DxC 800 and AU 5822 platforms. Imprecision was assessed using 20 replicate measurements of three low-level control samples, from 0.8 – 1.5 g/dL of total protein, and 0.8 – 1.0 g/dL of albumin. Method comparisons were assessed in 46 samples with a concentration range between 1.1 – 7.6 g/dL of total protein, and 48 samples with a range of 1.0 – 3.2 g/dL of albumin. Statistical analysis was carried out with EP Evaluator 12.3.02. Results The observed means for total protein ranged from 0.78 to 1.54 g/dL, with SDs between 0.02 and 0.05 g/dL, leading to CVs from 2.8% to 5.3%. Means for albumin ranged from 0.80 to 1.0 g/dL, with SD at 0.0 g/dL and CV at 0%, demonstrating acceptable precision for both assays. Linearity was exhibited at a concentration range from 0.72 – 12.50 g/dL (total protein), and 0.20 – 4.55 g/dL (albumin). Method comparison results showed high correlation, with an R value of 0.9951 (total protein), and 0.9152 (albumin). For total protein, the slope of 1.021 and intercept of 0.10 g/dL suggests minimal positive bias in the AU 5822 measurements compared to the DxC 800. For albumin, the slope was 1.056, and an intercept of -0.09, also displays minimal bias. Conclusion The Beckman AU platform is suitable to report total protein and albumin in peritoneal fluid at values <3.0 g/dL for total protein, and <1.5 g/dL for albumin, with exceptional precision and linearity performance. Overall, the expanded lower reportable range on the Beckman AU will allow for a higher level of diagnostic capability for SBP in patients with ascites in cirrhosis, highlighting the need for manufacturers to continuously evaluate and enhance the capabilities of their instruments to meet diagnostic needs.