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Acute on chronic kidney disease in cats

Chen H, Dunaevich A, Apfelbaum N, Kuzi S, Mazaki‐Tovi M, Aroch I, et al. Acute on chronic kidney disease in cats: Etiology, clinical and clinicopathologic findings, prognostic markers, and outcome. J Vet Intern Med [Internet]. 2020 May 22.

While chronic kidney disease (CKD) is one of the most common illnesses of older cats, its pathogenesis and progression remains poorly understood. Among the significant questions is whether CKD progresses as a slow, gradual decline in renal function or as a series of acute episodes leading to a stepwise progression. One of the more common complications of CKD is the development of “acute on chronic kidney disease”, episodes of sudden decline in renal function and health status in a cat with CKD that closely mimic the appearance of acute kidney injury (AKI). An understanding of these acute-on-CKD (ACKD) episodes is important in order to allow owners to make informed treatment decisions and veterinarians to treat and prognosticate.

The purpose of this paper was to characterize the etiology, clinical and laboratory findings, and prognosis of cats with ACKD. It was designed as a retrospective observational study of cats presenting to a veterinary teaching hospital over a two year period with a diagnosis of ACKD. Eligibility criteria included acute onset of clinical signs of AKI, azotemia, and one of: a previous diagnosis of CKD with an acute increase in creatinine of at least 20%; previous diagnosis of CKD with urinary evidence of AKI (ie cylindruria, glycosuria with normoglycemia); or unequivocal ultrasound findings consistent with CKD.

Etiology of ACKD was categorized as ureteral obstruction, pyelonephritis, renal ischemia, “other” renal etiology, or unknown. The “other” group included cats with cardiorenal syndrome, infected cysts, and protein losing nephropathy. Survival was defined as live discharge form hospital; cats who died or were euthanized due to disease were grouped together. Animals euthanized in the first 48h after admission were excluded. Long term outcome was determined as number of days after discharge to death or euthanasia. Cats lost to follow up were censored.

ACKD was diagnosed in 159 cats in the study period, of which 30 were excluded due to short hospital time, and 29 were excluded due to incomplete medical records precluding adequate diagnosis. 100 cats were therefore included in the final analysis.

The most common clinical signs were anorexia, weight loss, lethargy, and vomiting. Clinical signs did not differ between survivors and non survivors. Rectal temperature was lower in survivors vs non survivors (36.6 vs 37.5 degrees). Mean duration of hospitalization was 5 days (range 2-26). Non survivors had a shorter hospitalization than survivors, but there was no difference in length of stay based on cause of disease. Pancreatitis (based on ultrasound or elevated DGGR) was present in 54% of cats, with no difference between survivors and non survivors.

Ureteral obstruction was identified in 11% of cats, ischemia in 9%, pyelonephritis in 8%, other in 6%, and unknown in 66%.

58% of cats survived to discharge; while 13% died of disease and 29% were euthanized. Under multivariate regression, only serum phosphorus was associated with risk of survival to discharge. The AUC of phosphorus as an outcome predictor was 68%, with a cutoff of 16.7md/dL (5.4mmol/L).

Follow up data was available in 53 survivors. Median survival time was 66 days, with 81% of cats surviving 6 months and only 8% surviving 12 months. In a multivariate regression model, only serum creatinine was associated with long term survival; every 1.0mg/dL (88.4mmol/L) increase in creatinine was associated with a 1.43 fold increase risks of death at any time point. IRIS AKI grade II and III cats had a survival time of 233 days, compared to 29 days for IRIS AKI grade IV or V.

Serum creatinine at discharge was also predictive of survival. Cats with IRIS I and II did not reach a median survival time at the time of publication; IRIS III and IV median survival times were 66 and 22 days respectively. Cats with ACKD due to ureteral obstruction had significantly longer survival times than all other etiologies combined.

While an adequate descriptive study, there were a few limitations present in this manuscript.  The retrospective nature limited sample size and amount of data collection available. While excluding cats euthanized in the first 48 is reasonable to avoid inclusion of cats euthanized prior to adequate therapy, it may also have excluded the sickest cats.  As a tertiary institution, the population may have been biased towards sicker cats who were no able to be treated by a primary or secondary care center.

Overall, this manuscript represents an overview of the causes and prognosis of ACKD in cats. The authors conclude that ischemia, pyelonephritis, and ureteral obstruction are common causes of ACKD in cats, though many remain unknown. The short term prognosis for ACKD is similar to AKI and is predicted best (though not well) based on admission phosphorus. Long term prognosis may be predicted based on creatinine (or its surrogate, IRIS stage) at discharge. (MRK)

See also:

Cowgill LD, Polzin DJ, Elliott J, et al. Is progressive chronic kidney disease a slow acute kidney injury? Vet Clin North Am Small Anim Pract. 2016;46:995-1013.

Yerramilli M, Giosi F, Quinn J, et al. Kidney disease and the nexus of chronic kidney disease and acute kidney injury. Vet Clin North Am Small Anim Pract. 2016;46:961-993.