Effect of storage time and temperature on the results of analysis of synovial and mesothelial fluids.
Authors: Hughes K J, Rendle D I, Higgins S, Barron R, Cowling A, Love S, Durham A E
Journal: Equine veterinary journal
Summary
# Editorial Summary: Storage Effects on Equine Body Fluid Analysis Delays between collection and laboratory analysis are routine in equine practice, yet their impact on diagnostic accuracy remained unexplored until Hughes and colleagues conducted this 2017 investigation. The team stored 32 synovial and mesothelial fluid samples from 23 horses at both 4°C and 22°C, then measured total protein concentration, total nucleated cell counts (TNCC) and neutrophil morphology at immediate analysis, 24, 48 and 72 hours post-collection. Whilst protein levels remained stable regardless of storage conditions, TNCC declined significantly—dropping at 72 hours when refrigerated and as early as 24 hours at room temperature—whilst neutrophil degeneration became progressively more pronounced across all storage timepoints and temperatures, with nine samples showing altered clinical interpretation. Although the test maintained perfect specificity and positive predictive value, sensitivity and negative predictive value deteriorated substantially with prolonged storage and warmer conditions, meaning that delayed analysis risks missing genuine disease whilst potentially generating false negatives. For practitioners, this reinforces the critical importance of submitting body fluids for analysis within hours of collection rather than days, particularly when ambient temperatures are elevated, to avoid preanalytical artefacts that could undermine diagnostic decision-making and patient management.
Read the full abstract on PubMed
Practical Takeaways
- •Send body fluid samples to the laboratory immediately after collection — delays of even 24-48 hours at room temperature can significantly alter cell counts and morphology, potentially leading to missed diagnoses
- •If sample submission cannot be immediate, refrigerate at 4°C rather than room temperature to slow cellular changes, though this only delays deterioration rather than preventing it
- •Be aware that delayed analysis may cause false-negative results; if clinical suspicion remains high but fluid analysis appears normal, consider resampling with immediate processing
Key Findings
- •Total protein concentration was unaffected by storage time and temperature
- •Total nucleated cell count significantly decreased at 72h (4°C) and 24-72h (22°C), with greater reduction at higher temperatures (P<0.001)
- •Neutrophil morphology grade significantly increased at all time points beyond baseline for both temperatures (P<0.001)
- •Diagnostic interpretation changed in 9 of 32 samples (28%) with delayed analysis; sensitivity and negative predictive value decreased with storage duration and temperature while specificity remained 100%