Early Clinical Data Highlights Potential Missed Kidney Injury Diagnoses
Kidney injury (KI) is linked to high morbidity and mortality in veterinary patients. But, until recently, the thought of accurately diagnosing a patient at the time of the insult seemed impossible. Besides the fact that cats and dogs can show a wide range of presentations, from few or no clinical signs to those with severe and even complete loss of kidney function, there are many causes of kidney injury. Those causes include primary renal insult and injury secondary to poor renal perfusion, and veterinarians have been challenged by the lack of diagnostic tests that identify the injury early and accurately.18 Historically, the diagnostic tools available to veterinarians could only diagnose kidney disease after it significantly advanced.
Now, we can do better through early detection with the novel kidney biomarker cystatin B, paired with aggressive clinical intervention. With case fatality rates as high as 60% in some patients, this shift in KI workups can help improve the prognosis for patients.18
What Is Cystatin B?
Veterinarians have long relied on a reactive lab workup for patients with suspected kidney injury. The traditional kidney disease functional biomarkers, creatinine and SDMA, reflect changes in the glomerular filtration rate. However, these changes may take days to occur; the consequence can be failure to detect and diagnose KI early.
Now, clinicians can take a more clinically proactive approach by adding a biomarker to their lab panel that increases with acute and/or active injury at the renal tubular level. Concentrations of cystatin B, a small ~11kDa intracellular protein, increase when released from damaged renal tubular epithelial cells.46 While the epithelial cells of the renal proximal tubule and the thick ascending loop of Henle are the most metabolically active part of the nephron, they are also some of the most vulnerable to damage.39 Therefore, when these renal tubular cells experience injury or toxicity and rupture, cystatin B is released into the urine for measurement.
Early Clinical Data
When a first-of-its-kind diagnostic to detect an emerging biomarker launches, especially for clinical use in an area of veterinary medicine that has previously been not diagnostically accessible, validation around precision and accuracy is important. This helps build trust with veterinarians as they think through use cases and workflow implementation.
A recent IDEXX study shows that 1 in 5 dogs and 1 in 7 cats tested had increased cystatin B results. While this statistic is powerful in its own right, what is even more eye-opening is that of those canine patients with increased cystatin B, 56.4% had functional markers within the reference interval—35.7% for feline patients6. This suggests the presence of subclinical active injury, warranting further investigation. In these cases where kidney injury may not have been clinically apparent, any chance for earlier detection and intervention would have been missed without cystatin B testing.
What Cystatin B Means for Canine and Feline Patients
Veterinarians are familiar with a standard chemistry panel and urinalysis and have easily integrated the addition of SDMA. Adding cystatin B to the same panel for patients with known or suspected kidney disease or injury complements the SDMA findings and may uncover subclinical injury. It gives us an earlier and more accurate assessment of the patient's status prior to the onset of clinical signs.
There are several indications for using the cystatin B test in veterinary patients. This test will have significant clinical value in canine and feline patients where kidney injury may have occurred. It will also benefit patients previously diagnosed with kidney disease to help distinguish between stable patients and those with progressive changes.46
However, primary kidney injury patients are not the only cases to screen. Many other nonrenal conditions may secondarily affect renal perfusion, including but not limited to hypotension, hypovolemia, fever, and vasculitis.39
As veterinarians think about how to maximize diagnostic intervention for canine and feline kidney patients, it's critical to have a thorough diagnostic database. Clinical data on how often cystatin B is increased in tested patients is still early and developing but noteworthy enough to suggest that this important biomarker should be a part of any suspected kidney injury workup. And as more panels include this biomarker, there will be more learnings to come for kidney health in patients.
References: https://www.thevetiverse.com/en/latest/sdma-references/
