Veterinary Diagnostics:

Important information about cortisol testing

Published: 29th October 2020

The manufacturer of the cortisol assay for the Immulite2000 analyser has made a change to the assay. This was done with very little notice to the veterinary laboratories that use their assay (most commercial labs in the country) allowing no time to plan and perform the necessary comparisons with the previous assay.

Since receiving the new assay last week all the labs in VPG have been running comparisons as a matter of urgency to see how this new assay compares with the previous one and how it will affect interpretive decisions.  The data we have obtained is also being fed into a national database organised by the European Veterinary Endocrinology Quality Assurance Scheme to try and come up with a consensus about how veterinary labs interpret cortisol values generated with the new assay.

Preliminary data suggests the new assay has a significant negative bias particularly at the lower end of the assay range (ie. cortisol values are measuring lower than the original assay) but the bias varies across concentrations.

Some labs have changed their reference interval as a result. We currently have chosen not to do this as investigations nationwide are still ongoing. Internal interpretive cut-offs will be continuously monitored as further data is generated.

The main impact is likely to be in the interpretation of a low cortisol value:

  • ACTH stimulation tests may be advised more frequently to exclude Addison’s disease and rule out oversuppression of the adrenal axis for dogs on ‘Vetoryl’ – Trilostane therapy.
  • Interpretation of LDDST may generate equivocal results more frequently.
  • Results with the new assay will not be directly comparable to previous results for a dog on long term cortisol monitoring.
  • Urine cortisol measurement shows a greater level of bias than serum cortisol and we will not currently offer this with the new assay. There may therefore be a delay in reporting UCCRs as they will have to be run on the original assay.

Some of our sites (VPG Exeter / VPG Leeds) still have plenty of the original assay available and consequently cortisol results are not yet affected. However other sites (VPG Hitchin / VPG Cork) are now using the new assay.

VPG Ringwood will not be affected by this change whilst they retain the use of an Immulite1000 analyser.

We will always inform you on the report if the cortisol result provided has been generated using the new assay and how it affects interpretation.

Interpretation of cortisol values for diagnosing adrenal disease will be more challenging until we better understand how the new assay compares to the previous one and we request you provide as much history as possible with any submissions to help with this.

The situation is constantly evolving as more data comparisons are performed.

We will keep you informed as to progress and how it affects cortisol interpretation.

Please feel free to contact the lab to speak to one of the pathologist if you would like more information and/or to discuss interpretation of individual cortisol results.

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