Stability of common biochemistry analytes in equine blood and serum stored at room temperature

Aims: To investigate the clinical relevance of changes in clinical chemistry analytes in equine clotted blood over time and determine whether separation of serum from clotted blood protects against artefactual changes. Methods: Samples of clotted blood and separated serum from 18 horses were stored and analysed at 0, 24, 48 and 72 hours. Additionally, samples from 8 horses were analysed twice at 0h to assess intrasample agreement. The mean bias and 95% limits of agreement were calculated, using bootstrapped data, to assess agreement between pairs of samples analysed at 0 hours, and each of 24, 48 and 72 hours, for clotted blood and separated serum. The same analyses were undertaken to assess intrasample agreement. These data were plotted (Bland-Altman plots) to explore general trends. Results were interpreted in light of the ‘expected’ agreement, determined from the intra-sample analyses, and pre-determined levels of variation that were considered to be of potential clinical relevance for each analyte. Results: In clotted blood increases in mean bias were evident over time for aspartate aminotransferase (AST), bile acids (BA), creatine kinase (CK), glutamate dehydrogenase (GLDH), lactate dehydrogenase (LDH), total protein (TP), total magnesium (tMg) and urea. Decreases were observed for glucose, serum amyloid A (SAA) and total bilirubin (tBIL). The 95% limits of agreement revealed that changes of potential clinical significance may occur for all of the analytes mentioned over most time points. Agreement was found to be better for all analytes when separated serum was used. Conclusions: Delays in processing equine blood may result in changes in biochemical analytes of clinical relevance. Practical Significance: Separation of serum following clot formation is advisable if delays in processing are anticipated. Clinical samples in which a delay in processing has occurred should be interpreted with reference to the data presented.