Differentiating between acute and chronic kidney disease - Veterinary Medicine
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Differentiating between acute and chronic kidney disease
When dogs and cats have kidney disease, it can be a puzzle determining whether the problem has just developed or has been ongoing. These diagnostics can help you piece the puzzle together to make that distinction so you can provide optimal care and give owners the most accurate prognosis for their pets.



Obtaining a thorough clinical history is useful in determining the chronicity of a patient's kidney disease. Polydipsia and polyuria are classic signs of kidney disease but are not present in all cases. Their presence does not differentiate AKI from CKD, but their duration may help distinguish between the two. In one study, 70% of cats with CKD presented with an owner complaint of polydipsia and 31% with polyuria.14 The discrepancy in owners' reporting of polydipsia more frequently than polyuria is likely because owners are better able to detect abnormalities in water consumption than abnormalities in urination volume or frequency. About half of dogs and cats with AKI are oliguric or anuric.12,13,15

Decreased appetite, vomiting, or other gastrointestinal signs can be associated with both AKI and CKD, but these signs would be of recent onset with AKI. In one study, decreased appetite was present in 33% and vomiting in 22% of cats with CKD.14 Often these signs were waxing and waning for months. In addition to complete refusal of food, other common signs include taking longer to eat or showing interest in food without actually eating. Historical weight loss suggests chronic disease, although owners frequently do not recognize weight loss when it is slowly progressive and subtle. Compensatory mechanisms can mask a great degree of the patient's clinical signs at home, leading owners to miss subtle changes. The history should also include questions about exposure to medications (administered or accidental) or possible toxins.


Figure 1. A cat with poor body condition secondary to CKD. Note the generalized severe muscle wasting, including the epaxial muscles.
A thorough physical examination can help differentiate between AKI and CKD. Initially, most patients with AKI without concurrent disease processes have a normal body condition. However, because kidney disease is a highly catabolic disease, muscle loss can occur rapidly. Although weight loss and poor body condition are not specific for kidney disease, a poor body condition with diffuse muscle wasting and an unkempt coat are often some of the first characteristics noted on physical examination of a patient with CKD (Figure 1). Palpation of the epaxial muscles often reveals subtle but marked muscle loss. Small, irregular kidneys on abdominal palpation support a diagnosis of CKD, while normal or large kidneys can be associated with either AKI or CKD.

The prevalence of hypertension is 9% to 93% in dogs with CKD16-21 and 19% to 65% in cats with CKD.22-24 With AKI, 87% of dogs25 and 30% of cats are hypertensive (Worwag S, Langston CE, Unpublished data, 2009). Thus, the presence of hypertension does not distinguish between AKI and CKD. Because the eyes are a target of hypertensive damage, retinal examination is indicated in any patient with renal disease and is quick and easy to do with an indirect lens. The most common ocular manifestation of systemic hypertension is exudative retinal detachment.26 Retinal edema can be seen as an early manifestation of systemic hypertension and appears as "pseudonarrowing" of retinal arterioles. Dilation and tortuosity of retinal vessels, retinal hemorrhage, retinal detachment, and retinal degeneration are seen more commonly with chronic hypertension.26,27 Identification of any of these ocular signs should prompt blood pressure measurement. Ocular lesions are identified in between 48% and 100% of cats and 20% and 62% of dogs with hypertension.24,28-32 Hypertensive retinopathy tends to gradually progress with chronic hypertension, but an acute rise in blood pressure may precipitate an acute exudative retinal detachment or hyphema.27

Clinical signs of CKD may be less pronounced when compared with those of AKI with the same level of azotemia,33 although we have observed that some patients with early AKI have minimal clinical signs, which worsen over the subsequent several days if recovery is not prompt. As with the patient history, the physical examination is just one of multiple pieces in this clinical puzzle.


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