Chronic kidney disease (CKD) is a common condition in cats, especially as they age. One of the major challenges in managing CKD is addressing proteinuria, which is the abnormal presence of protein in the urine. Proteinuria can worsen kidney damage and is associated with a poorer prognosis in affected cats. Managing proteinuria effectively can help slow disease progression and improve quality of life.
What Causes Proteinuria in CKD?
Proteinuria in CKD occurs when the kidneys' filtering units (glomeruli) are damaged, allowing proteins, particularly albumin, to leak into the urine. This leakage not only signals worsening kidney function but also contributes to further inflammation and fibrosis in the kidney's tissues. These processes can speed up the progression of CKD.
How Is Proteinuria Detected?
We commonly assess proteinuria by measuring the urine protein-to-creatinine ratio (UPCR) in cats suspected of having CKD. Routine urine dipstick tests are not reliable for detecting proteinuria in cats, so UPCR is the preferred method. UPCR values help categorise proteinuria as:
- Non-proteinuric (UPCR < 0.2)
- Borderline proteinuric (UPCR 0.2–0.4)
- Proteinuric (UPCR > 0.4)
Cats with higher UPCR values generally have shorter survival times. For instance, one study showed that cats with a UPCR greater than 0.4 had a median survival time of around 400 days compared to roughly 1000 days for those with a UPCR below 0.2 (1).
Why Is It Important to Control Proteinuria?
Reducing proteinuria is important because it helps slow the progression of CKD. In human and canine medicine, controlling proteinuria has been shown to improve kidney function and extend life expectancy, and while feline studies are more limited, the available evidence suggests similar benefits in cats.
Treatments to Manage Proteinuria in Cats with CKD
Treatment strategies for managing proteinuria in CKD often involve medications that target the renin-angiotensin-aldosterone system (RAAS). These drugs reduce blood pressure within the kidneys' filtering units, lowering the amount of protein lost in urine. Two classes of RAAS-inhibiting drugs are commonly used:
1. Angiotensin-Converting Enzyme Inhibitors (ACEIs):
- ACEIs, such as benazepril, have been shown to reduce proteinuria in cats with CKD. However, these drugs may not always improve survival rates, and further studies are needed to determine their full effects.
2. Angiotensin Receptor Blockers (ARBs):
- Telmisartan is an ARB recently licensed for use in cats with proteinuria. Studies have shown that telmisartan significantly reduces proteinuria, making it a promising treatment option.
Monitoring and Managing Treatment
It's important to carefully monitor cats receiving RAAS-inhibiting drugs. Regular checks of kidney function (creatinine levels) and blood pressure should be done within a week of starting treatment or adjusting doses. This helps ensure that the treatment is effective and that there are no adverse effects, such as worsening kidney function or low blood pressure. In some cases, proteinuria may decrease after successful treatment of high blood pressure, reducing the need for further antiproteinuric medications.
Risks and Considerations
While RAAS inhibitors are generally well-tolerated, they must be used with caution in cats with advanced CKD (Stage 4). Potential side effects include increased blood creatinine levels, hypotension, and, rarely, hyperkalemia. It’s also important to avoid using RAAS inhibitors in conjunction with non-steroidal anti-inflammatory drugs (NSAIDs), as this combination can increase the risk of acute kidney injury.
Reference:
Syme, H. M., Markwell, P. J., Pfeiffer, D., & Elliott, J. (2006). Survival of cats with naturally occurring chronic renal failure is related to severity of proteinuria. Journal of Veterinary Internal Medicine, 20(3), 528-535.
Take a moment to read our other blog posts about other important management aspects of CKD: