A new study, published in the latest issue of the Journal of Small Animal Practice (JSAP), found that relying on total calcium concentrations alone to diagnose dogs with ionised hypercalcaemia may result in misclassification in around one third of dogs.

Investigation of the relationship between ionised and total calcium in dogs with ionised hypercalcaemia1 was undertaken by Tørnqvist-Johnsen et al. at the Hospital for Small Animals, University of Edinburgh, UK.

Initially, a normal reference interval for ionised calcium, total calcium and albumin, serum and plasma biochemistry was established by analysing samples from 351 healthy adult dogs.

After establishing a reference interval for ionised calcium, the laboratory’s database was searched for adult dogs with ionised hypercalcaemia that had attended the university small animal hospital between 2012 and 2017, a time frame when the same sample handling protocols and instrumentation was in use. The hospital records were searched for patient information and the biochemical parameters statistically analysed.

Of 63 dogs identified with ionised hypercalcaemia, 23 did not have a total hypercalcaemia (37%). 16 of these 23 dogs (70%) had albumin within the reference interval. To summarise the key findings; using total calcium, one third of patients with ionised hypercalcaemia were not identified. There was also no significant relationship between albumin and total calcium in these cases.

Camilla Tørnqvist-Johnsen, lead author of the paper, said: "Hypercalcaemia is a very important clinical abnormality, often revealing severe underlying disease in dogs who do not get idiopathic hypercalcaemia. This study reveals the true importance of doing an ionised calcium measurement when evaluating calcaemic status."

Nick Jeffery, Editor of JSAP said: "This study demonstrates that, if relying on total calcium alone, more than one third of dogs with ionised hypercalcaemia will be classified as normocalcaemic. Furthermore, the study demonstrates that the discordance between ionised and total calcium cannot be routinely explained by a low protein-bound component.

"Whilst reference intervals are key in clinical practice to determine whether a result is an outlier from 95% of a healthy population, it is not inevitable that a patient with an outlying biochemical test result has a clinically relevant disease."

The full article can be found in the April issue of the Journal of Small Animal Practice which is free for BSAVA members. It can also be read online here: https://onlinelibrary.wiley.com/doi/10.1111/jsap.13109 

Reference

  1. C. Tørnqvist-Johnsen, T. Schnabel, A. G. Gow, J. Del-Pozo, E. Milne, V. Macklin, C. Fisher, I. Handel and R. J. Mellanby (2020) Investigation of the relationship between ionised and total calcium in dogs with ionised hypercalcaemia. Journal of Small Animal Practice, 61 (4). Available at: https://onlinelibrary.wiley.com/doi/10.1111/jsap.13109    

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