Study questions urine sodium as a stage B2 MMVD marker: full analysis

A new Frontiers in Veterinary Science study adds a cautionary note to the search for easier biomarkers in canine heart disease: spot urinary sodium indices did not reliably distinguish healthy dogs from dogs with ACVIM stage B2 myxomatous mitral valve disease. In the prospective cross-sectional study, researchers evaluated urinary sodium concentration, the urine sodium-to-potassium ratio, and a corrected urine sodium index, and concluded that none performed well enough to separate preclinical B2 MMVD from healthy controls in routine practice. (frontiersin.org)

That matters because stage B2 is a pivotal threshold in MMVD care. Under the 2019 ACVIM consensus guidelines, stage B2 refers to asymptomatic dogs with mitral regurgitation severe enough to produce left atrial and ventricular enlargement, and it’s the subgroup for which pharmacologic treatment is recommended to delay progression to heart failure. The push to find simpler biomarkers reflects a real clinical need: identifying B2 disease can require echocardiography, radiographs, and careful interpretation, which may not be equally accessible in every practice setting. (vdc.vet)

According to the Frontiers report, the investigators specifically asked whether spot urine sodium-related indices could act as practical markers of neurohormonal status in preclinical MMVD. They found they did not significantly differ between healthy dogs and dogs with stage B2 disease, and they showed limited utility overall. The study also examined relationships between those urinary markers and echocardiographic variables including left atrium-to-aorta ratio, normalized left ventricular dimensions, and transmitral flow measures, but those associations were not strong enough to support clinical use as a differentiating tool. (frontiersin.org)

The findings fit with a broader pattern in MMVD biomarker research: promising physiologic ideas don’t always translate into clinically useful staging tests. Prior work has also shown that urinary aldosterone-to-creatinine ratio did not significantly differ among healthy dogs and dogs with stage B1, B2, or C MMVD, despite interest in renin-angiotensin-aldosterone system activation as disease progresses. That doesn’t rule out neurohormonal change in preclinical disease, but it does suggest that single spot urine measures may be too variable, too indirect, or too influenced by routine conditions to function as reliable stand-alone staging tools. (link.springer.com)

For clinicians, the practical takeaway is straightforward: don’t expect spot urinary sodium indices to help sort a murmur patient into or out of stage B2. That’s especially relevant because getting B2 classification right has treatment implications. The EPIC trial showed pimobendan extended the time to onset of congestive heart failure or cardiac-related death in dogs with preclinical MMVD and cardiomegaly, and FDA’s conditional approval materials likewise frame stage B2 MMVD as the key preclinical treatment window. (pubmed.ncbi.nlm.nih.gov)

Why it matters: In primary care, there’s strong appeal to a low-friction urine test that could flag which asymptomatic dogs need referral or earlier intervention. This study argues that urinary sodium indices aren’t ready for that role. For veterinary professionals, that reinforces the importance of disciplined staging based on murmur assessment, thoracic imaging when indicated, and echocardiographic criteria aligned with ACVIM guidance. It also helps prevent overinterpretation of lab data that may look biologically plausible but don’t meaningfully change case management. (vdc.vet)

No outside expert reaction specific to this paper was readily available at the time of review, but the broader field remains focused on finding scalable ways to identify B2 dogs earlier and more accurately. That includes work on circulating biomarkers, imaging refinement, and disease progression models, all aimed at narrowing the gap between first murmur detection and definitive staging. (frontiersin.org)

What to watch: The next step is likely not more enthusiasm for spot sodium testing, but more targeted work on multimodal biomarkers or better referral-stage screening tools that can complement, rather than replace, echocardiography in preclinical MMVD. (frontiersin.org)