Comparison of paired serum and lithium heparin plasma samples for the measurement of serum amyloid A in horses using an automated turbidimetric immunoassay.
Authors: Howard Judith, Graubner Claudia
Journal: Veterinary journal (London, England : 1997)
Summary
Serum amyloid A (SAA) is a valuable acute-phase marker in equine practice, but sample type can affect laboratory results and clinical decision-making. Howard and Graubner evaluated whether lithium-heparin plasma could reliably substitute for serum when measuring equine SAA via automated turbidimetric immunoassay, analysing paired samples from 40 horses using statistical methods including Passing-Bablok regression and Bland-Altman analysis. The two sample types yielded virtually identical SAA concentrations (correlation coefficient 0.97, P<0.0001), with no statistically significant difference between them, though plasma showed a small positive bias relative to serum that fell below clinical significance thresholds. This finding offers practical flexibility for practitioners—plasma samples are often easier to obtain and handle in field settings—though direct comparison of results between serum and plasma measurements should be approached cautiously, particularly when tracking longitudinal changes in individual cases. For farriers, vets, and other professionals using SAA as a diagnostic or monitoring tool in inflammatory or systemic conditions, either sample type is now validated, provided collection and handling protocols are consistent within each patient's clinical record.
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Practical Takeaways
- •Either serum or lithium-heparin plasma can be used for SAA measurement in horses, providing flexibility in sample collection protocols
- •Results are interchangeable between sample types for clinical purposes, though practitioners should note plasma slightly higher values
- •This validation allows clinicians to choose sample type based on laboratory workflow and collection practicality without affecting diagnostic reliability
Key Findings
- •No statistically significant difference in SAA concentrations between serum and lithium-heparin plasma samples (P=0.48)
- •Strong correlation of 0.97 between paired samples (Spearman's rank P<0.0001; 95% CI 0.95-0.99)
- •Bland-Altman analysis showed positive bias in plasma compared to serum but difference was not clinically significant
- •Lithium-heparin plasma samples are suitable for automated turbidimetric measurement of equine SAA