Chronic kidney disease in cats: Hypokalemia, signs, the exam, and staging

Photo: Evrymmnt/Adobe Stock

Understanding chronic kidney disease (CKD)—one of the most common diseases in older cats—is an important task. At the 2025 Fetch dvm360 Conference in Charlotte, North Carolina, Christopher Byers, DVM, offered a comprehensive lecture on CKD in felines. Highlights of his session include understanding signs of hypokalemia in patients with CKD, the clinical presentation of the disease, the physical exam, and IRIS staging.

Hypokalemia in patients with CKD

Hypokalemia in cats without CKD and those with the condition may present in different ways, with the manifestation including cervical ventroflexion, paresis, and a stiff gait. During his session, Byers explained that hypokalemia is one of the differentials for cervical ventral flexion, which renders a cat unable to lift their head up.¹ However, as Byers emphasized, hypokalemia does not manifest itself through cervical ventral flexion in the typical cat with CKD.

Instead, “the typical CKD cat may have their hypokalemia manifest as just lethargy—just reduced activity—or very commonly, at least stiff gait,” Byers emphasized.

Many owners of patients with CKD may believe their cat’s stiff gait is because of arthritis in old age. However, as Byers stressed, in cases where the patient is documented or suspected to have CKD, it is imperative to check the patient’s potassium status, as these signs raise a red flag.

“Sometimes patients at the low end of normal—so 3.4, 3.5 [mEq/L]—maybe [even] that is...too low and we want to push them toward the middle range of the reference range, or the upper part of the reference range,” Byers said. “...Potassium supplementation for these patients is often needed.”

Clinical presentation of CKD

A patient with CKD “can look like a completely normal cat or dog,” Byers said. In the early stages of the diseases, polyuria and polydipsia (PUPD) is the most common clinical sign, with polyuria being primary and polydipsia being compensatory. Clients may report not being able to keep the cat’s water bowl full, finding more clumps in the litter box, and having to change the litter box more often.¹ “But that may be the only sign,” expressed Byers.

When conducting a serial exam, weight loss may be noted by the veterinarian. “Owners may not recognize that their pet is losing weight because they're looking at them every day,” added Byers.

As the disease progresses, the patient may exhibit the following clinical signs¹:

• Vomiting
• Weight loss
• Hypo-/anorexia
• Lethargy
• Diarrhea
• Urinary incontinence
• Weakness
• Halitosis
• Dysphagia

Byers explained that except for uremic halitosis, none of these clinical signs are pathognomonic for CKD.

Physical exam

Must do’s

“What I want to emphasize, [is] look for the stiff gait issues in the senior and geriatric patients, and always do a fundus exam,” stressed Byers.

“The why is, obviously, you're looking for the overt changes, like a retinal detachment,” he continued. “But sometimes, you're going to be able to pick up on some subtle things, like retinal vessel tortuosity that gives a red flag that, oh, ‘I'm really concerned about systemic hypertension....’”

As Byers explained, the fundus exam will not always show an overt retinal hemorrhage or detachment, but rather “very subtle retinal changes that give [the veterinarian] red flags and justification for sharing more information with the owner about some additional investigation to do for those patients.”

Other things to look for

During the physical examination, veterinarians should look for the following¹:

• Dehydration
• Irregular renal atrophy
• Generalized sarcopenia
• Oral ulcerations, due to uremia
• Pale mucous membranes, caused by anemia
• Tachypnea, due to anemia and/or metabolic acidosis
• Halitosis, due to uremia

IRIS Staging

The CKD IRIS staging for cats, a presented by Byers, is as follows¹:

Stage 1

• Creatinine (CREA): <1.6 mg/dL (<141.5 umol/L)
• Symmetric dimethylarginine (SDMA): <18 ug/dL

Stage 2

• CREA: 1.6-2.8 mg/dL (141.5-247.6 umol/L)
• SDMA: 18-25 ug/dL

Stage 3

• CREA: 2.9-5.0 mg/dL (256.4-442.1 umol/L)
• SDMA: 26-38 ug/dL

Stage 4

• CREA: >5.0 mg/dL (>442.1 umol/L)
• SDMA: >38 ug/dL

As patients with CKD begin to lose muscle mass, SDMA may be a more reliable indicator of stage in patients with sarcopenia, explained Byers.

IRIS sub-staging

“There’s also sub-staging that [we] need to do,” Byers said. For feline patients with or without proteinuria, the sub-staging is as follows¹:

• Non-proteinuric: <0.2 urine protein-to-creatinine ratio (UPC)
• Borderline proteinuric: 0.2-0.4 UPC
• Proteinuric: >0.4 UPC

For hypertension, the IRIS sub-staging, relative to blood pressure, is as follows¹:

• Normotensive: <140 mmHgn
• Pre-hypertension: 140-159 mmHg
• Hypertension: 160-179 mmHg
• Severe hypertension: >180 mmHg

Takeaways

Patients with CKD may not exhibit any signs, with PUPD being the most common sign in patients in the early stages of the disease. Veterinarians should be careful to note if the patient has a stiff gait, as this may indicate hypokalemia in a feline patient with CKD. Moreover, a fundus exam should also be conducted, as some findings could indicate systemic hypertension.

Reference

1. Byers CG. Chronic kidney disease. Presented at: Fetch Charlotte; Charlotte, North Carolina. March 14-16, 2025.