scott@vtx-cpd.com

Replying to Jane Sedgewick 14/05/2025 - 12:07

Hi Jane,

Thank you so much for the great questions. You are definitely not a pest. It’s fantastic that you’re getting so much out of the course.

You’re absolutely right that when you have a collapsed dog with marked hyperkalaemia and hyponatraemia, Addison’s becomes the top differential, especially in the presence of classic clinical signs like lethargy, vomiting, bradycardia, and hypovolaemia. Very few diseases give you that combination in a sick dog. Once sodium is low and potassium is genuinely high (not an artefact), Addison’s should be considered the most likely diagnosis unless something else clearly explains it, like urinary obstruction or acute kidney injury.

That said, regarding your question about differentials for a low basal cortisol, there are a few scenarios where this might occur without true Addison’s:

Critical illness-related corticosteroid insufficiency (CIRCI) is increasingly recognised in dogs with sepsis or SIRS. These dogs may have a flat or blunted ACTH stim but are not Addisonian. A 2021 study by Marchetti et al. found that CIRCI occurred in nearly 50% of dogs with SIRS and was associated with increased CRP and band neutrophils, but not necessarily with hypotension or mortality. Importantly, these dogs may have low delta cortisol on ACTH testing, so we need to interpret results carefully in the ICU setting.

Reference: Marchetti M, Pierini A, Favilla G, Marchetti V. Critical illness-related corticosteroid insufficiency in dogs with systemic inflammatory response syndrome: A pilot study in 21 dogs. Vet J. 2021;273:105677. doi:10.1016/j.tvjl.2021.105677

Iatrogenic suppression from prior steroid treatment, even topical creams or ear medications.

Sampling variation. Basal cortisol is highly dynamic and a low result can sometimes occur transiently in otherwise healthy or mildly stressed animals.

Hepatic dysfunction or severe systemic illness, which can affect cortisol metabolism or binding proteins.

That’s why, even in the face of compatible electrolytes and clinical signs, a low basal cortisol doesn’t confirm Addison’s. It just tells us we can’t rule it out. That’s where the ACTH stim is still essential. On the flip side, a basal cortisol above 55 nmol/L (around 2 µg/dL) is very helpful to exclude Addison’s.

The combination of all three in a collapsed dog dose make Addison’s the most likely thing! It’s questions like this that make the course better, so please do keep them coming.

Happy Sunday!

Scott 🙂

Replying to Anna M. 13/05/2025 - 09:31

Hi Anna,

The connection between hypothyroidism and fructosamine lies in how thyroid hormone levels influence protein metabolism, particularly albumin turnover. Fructosamine reflects the average blood glucose over the preceding two to three weeks by measuring the degree of glycation of circulating proteins, especially albumin. In hypothyroid dogs, there is a reduction in protein turnover, including albumin, which can result in artificially elevated fructosamine levels that do not accurately reflect glycaemic control. This can make it appear as though a diabetic dog is poorly regulated when, in fact, glucose levels may be acceptable.

So in dogs with concurrent hypothyroidism and diabetes, fructosamine may overestimate average blood glucose, particularly if the hypothyroidism is not well controlled. For monitoring these patients, I generally recommend placing greater emphasis on home blood glucose curves or using continuous glucose monitoring if available, as these provide real-time data that are not influenced by protein metabolism. It’s also important to ensure that the hypothyroidism is well managed and that T4 levels are within the therapeutic range before placing much weight on fructosamine values. If fructosamine is used, it should be interpreted cautiously and in the context of clinical signs, body weight trends, and serial blood glucose data, rather than in isolation.

I hope this helps clarify the connection, and I’d be happy to discuss further if helpful. Let me know how you are getting on with the course.

Best regards,

Scott 🙂

Replying to Jane Sedgewick 06/05/2025 - 16:46

Hi Jane,

Great question! t’s something many of us are wrestling with as SDMA becomes a routine part of senior wellness panels. I completely agree, identifying early kidney changes is only worthwhile if we know what to do with that information, and the evidence on early intervention, particularly before azotaemia, is still catching up. IRIS Stage 1 CKD is now formally recognized and includes patients with persistent renal changes like proteinuria or elevated SDMA in the absence of azotaemia. While we don’t yet have large prospective studies showing that intervention in these cases extends lifespan, there is growing support for the idea that earlier detection allows us to modify risk factors and potentially slow progression. Interventions might include addressing proteinuria with ACE inhibitors or ARBs even before creatinine rises, ensuring optimal hydration (especially in older or low body condition dogs), and, in selected cases, adjusting diet to moderate phosphorus and protein intake, though timing of dietary change is still a debated topic.

That said, in real-world clinical practice, I rarely find myself asking for SDMA unless it’s already included in a panel. Most of the dogs I see already have obvious disease, and if they’re azotemic, then SDMA really adds little, its value as an early biomarker becomes moot.

But for earlier-stage cases, especially the older dog who “seems well” but turns up with a borderline USG and mildly elevated SDMA, it does prompt more thoughtful discussion. Ideally, I think SDMA is most useful when paired with urine findings and muscle condition score as part of a broader screening protocol. A persistently elevated SDMA across timepoints, particularly in the presence of proteinuria or low USG, is much more convincing than a single raised value. That layered context helps distinguish signal from noise and guides whether to start more frequent monitoring, recommend dietary changes, or even consider ACE inhibition pre-emptively.

Are you seeing more cases now where SDMA is elevated in isolation? How are you deciding when to act and when to wait?

I hope you are having a lovely weekend.

Scott 🙂

Replying to Yvonne McGrotty 10/05/2025 - 16:40

I consider Britney to be a legend too… she is still in her 40’s!

Scott 🙂