AB Vista: Building Trust in Enzyme Recovery Testing — Our Interlaboratory Study Approach
At AB Vista, we are dedicated to helping our customers achieve accurate, reliable, and consistent enzyme recovery results. Our proprietary methods - adopted by customer laboratories worldwide - include ELISA-based assays (enzyme-linked immunosorbent assay – a biochemical technique used to detect and quantify specific proteins) for our phytase Quantum® Blue and xylanase Econase® XT, along with wet chemistry techniques for other enzymes in our portfolio. To give our customers added confidence, we run annual interlaboratory studies that allow participating labs to benchmark their performance, validate their results, and fine-tune their techniques with our expert support. These studies not only strengthen quality control but also enable us to set new method standards and analytical limits, ensuring our customers stay at the forefront of precision testing.
A robust study design for real-world insights
Our interlaboratory studies emulate everyday laboratory conditions to ensure real-world relevance. Each participating laboratory is provided with centrally prepared control samples to reduce composition variability, and conducts analyses using its own equipment, reagents, and staff. The specific method—such as the Quantum® Blue ELISA—depends on each exercise's focus.
A recent exercise involved 28 laboratories (24 customer labs and 4 internal labs). Each lab analysed three extractions per sample per week over two weeks. Two duplicate reactions were performed per extraction and averaged to yield one result, totalling six reported data points per sample. Altogether 168 data points were obtained, enhancing the rigor of analyses for repeatability and reproducibility.
A comprehensive statistical framework
To evaluate the performance of each lab, a rigorous statistical framework is employed to identify variability and ensure reliable results:
• Z-score Analysis: Z-scores measure each lab's results relative to the consensus mean and standard deviation. A Z-score close to zero signifies strong alignment, and scores within ±2 are usually considered acceptable. Figure 1 shows the Z-scores for all 28 laboratories, marking those beyond this limit as potential analytical or sample-handling issues.
• Normality Verification: The Shapiro-Wilk test confirms the normality of enzyme recovery distributions, ensuring the appropriateness of applying Z-scoring, a parametric method.
Figure 1: Z-scores from 28 participating laboratories in AB Vista's Quantum Blue ELISA interlaboratory study. Laboratories are anonymised from 1 to 41, and each lab's individual Z-score is plotted.
• Outlier Detection: Grubb's test identifies outliers, which are excluded before further analysis to ensure robust results.
• Advanced Variability Analysis: Mandel's h and k statistics respectively assess inter- and intra-lab variation, offering insights into systematic and random errors. A one-way ANOVA is used where relevant to reveal performance differences between laboratories.
Setting control limits for control samples
To establish reliable benchmarks, we set control limits for control samples like "Diet 1" based on the interlaboratory study results. After verifying normality with the Shapiro–Wilk test, Grubbs' test is applied to remove outliers. Control limits, set at the mean ±2 SD from laboratories with acceptable Z-scores (±2), provide a realistic performance benchmark. By first confirming data quality and removing outliers, we set control limits based on real-world performance from consistently reliable laboratories. The combination of Z-scores, Shapiro-Wilk, Grubb's test, Mandel's h and k, and ANOVA ensures a comprehensive evaluation, distinguishing procedural inconsistencies from genuine variability. The resulting control limits provide a clear benchmark for consensual performance with our customers, which is important to achieve more reproducible phytase and xylanase recoveries in feed formulation.
Figure 2: Scatterplot of enzyme recovery averages for the 'Diet 1' control sample across laboratories, with population standard deviation bands (±1 SD to ±3 SD) overlaid to illustrate variability and highlight potential outliers.
A positive outcome, no matter the results
In our recent study, many laboratories reported enzyme recovery results closely clustered around the group median, indicating strong consistency and offering a valuable benchmark to enhance confidence in applying our products. At the same time, our Technical Services team reached out to labs that showed variability or deviations to identify the cause and refine processes together, ensuring a positive outcome to all participants of this interlaboratory study. Our goal is to help customers align with industry benchmarks through consistent support and guidance.
AB Vista is committed to continuous improvement. We continually monitor customer recovery trends over time to detect and correct performance shifts early. By refining our statistical framework and expanding participation to more customer labs, we endeavour to foster a connected, quality-focused network. Working together in this way enhances standards, builds trust, and delivers lasting value to customers.