Analytical validation of a new point-of-care assay for serum amyloid A in horses.
Authors: Schwartz D, Pusterla N, Jacobsen S, Christopher M M
Journal: Equine veterinary journal
Summary
Serum amyloid A (SAA) is a sensitive marker of systemic inflammation in horses, and point-of-care testing could facilitate rapid assessment of acute phase response in clinical settings; however, the analytical performance of the new Stablelab POC assay had not been rigorously evaluated. Researchers validated the Stablelab assay against a reference turbidimetric immunoassay using equine serum, plasma and whole blood samples, testing linearity, intra- and inter-assay precision, and agreement between sample types. The POC test demonstrated excellent linearity up to 1000 µg/mL (r = 0.991) and acceptable intra-assay precision (13–18% coefficient of variation), but inter-batch precision at high SAA concentrations was poor (45%), and results from whole blood samples were significantly lower than serum/plasma with proportional negative bias above 500 µg/mL. Clinically, this means the Stablelab is suitable for point-of-care serum or plasma testing with good repeatability for individual samples, but users should be cautious about comparing results between test batches when tracking SAA trends in severe inflammation, should not interchange sample types (whole blood versus serum), and should avoid direct comparison with laboratory-based turbidimetric methods. Whilst the POC test offers convenience for stall-side assessment, these limitations warrant awareness—particularly when serial measurements guide management decisions in cases of colic, sepsis or other systemic disease.
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Practical Takeaways
- •The POC test can be used for SAA measurement in equine serum/plasma, but whole blood results are not interchangeable and should not be compared directly with serum/plasma or reference laboratory values
- •If serial SAA monitoring is needed, use samples from the same test batch to minimize inter-batch variability, especially at high concentrations indicative of severe inflammation
- •This POC test cannot reliably replace the reference turbidimetric immunoassay for definitive SAA quantification; consider it a screening tool rather than a gold standard for clinical decision-making
Key Findings
- •The Stablelab POC test demonstrated linearity up to 1000 μg/mL SAA with acceptable accuracy and precision in equine serum/plasma (r = 0.991)
- •Intra-assay CVs ranged from 13-18% across concentration ranges, but inter-batch CV at high concentrations reached 45%, raising concerns about serial monitoring
- •SAA results in whole blood were significantly lower than serum/plasma (P = 0.0002) with proportional negative bias above 500 μg/mL, limiting stall-side utility
- •Comparison between the POC test and reference turbidimetric immunoassay is not recommended due to method differences exceeding combined imprecision