Potassium

Quick Answer: Potassium imbalances are one of the most common electrolyte problems in cats with CKD. Low potassium (hypokalaemia) affects roughly 30% of CKD cats and can cause muscle weakness, an inability to hold the head up, and lethargy. High potassium (hyperkalaemia) affects around 13% of CKD cats, most often those in advanced IRIS Stage 4, and carries serious cardiac risks. Both directions are manageable when caught early through routine bloodwork. The goal is to keep potassium firmly in the middle of the reference range, around 4.0 to 4.4 mEq/L, rather than simply within it.

Potassium is an electrolyte that works alongside sodium to regulate nerve and muscle function throughout the body. Because the heart is a muscle, potassium plays a direct role in maintaining a stable heart rhythm. When levels drift too far in either direction, the consequences can be serious.

In cats with CKD, potassium imbalances are especially likely because the kidneys play a central role in regulating how much potassium the body retains or excretes. Damaged kidneys handle this job less reliably, which is why potassium levels in CKD cats need to be monitored regularly rather than assumed to be stable.

Low potassium can damage kidney tissue directly and may cause CKD to progress more quickly. It can also contribute to metabolic acidosis and hypertension, both of which place additional strain on already-compromised kidneys. High potassium, on the other hand, can disturb the heart rhythm in ways that, at extreme levels, become life-threatening.

Studies suggest that around 30% of CKD cats develop low potassium levels at some point during their illness, typically in the earlier IRIS stages. This happens because potassium is continuously lost through the increased urination that accompanies CKD, and vomiting compounds that loss further.

High potassium levels are less common overall but become more likely as CKD advances. Around 13% of CKD cats have hyperkalaemia, and the risk rises sharply in IRIS Stage 4, where the glomerular filtration rate has dropped low enough that the kidneys can no longer excrete potassium efficiently.

It is worth noting that some cats never develop a potassium imbalance at all, and others may move from normal levels to low levels to high levels as their disease progresses. This is why a single normal reading does not mean potassium can be dropped from future bloodwork panels.

Potassium is measured through a standard blood panel and may be listed as K or K+ (from kalium, the Latin word for potassium). The units are mEq/L in the United States and mmol/L internationally, but the numeric values are equivalent, so 4.0 mEq/L and 4.0 mmol/L represent the same concentration.

Most laboratory reference ranges sit somewhere between 3.5 and 5.5, but for cats with CKD the goal is to keep potassium around 4.0 to 4.4 rather than simply inside the reference interval. A result at the low end of the range still warrants attention, because the regulatory mechanism in the body prioritises maintaining potassium in the bloodstream over maintaining it inside the cells where it is actually used. This means that blood potassium can appear normal while the cells themselves are already depleted.

A few things can distort the result. A haemolysed sample, where the red blood cells have ruptured before testing, can push the reading artificially high. A sample that sat for a while before analysis can do the same. Metabolic acidosis can cause potassium to appear elevated in the blood even when the underlying tissue levels are low, and that apparent elevation may fall back down once the acidosis is treated.

Ask your vet to include potassium on every routine bloodwork panel. Many laboratories do not measure it automatically, and it is worth requesting it explicitly.

Causes

The most common reason CKD cats develop low potassium is simple loss through urine. As kidney function declines, urine output increases and potassium leaves the body at a faster rate than it can be replaced through diet. Vomiting accelerates this process further, and a cat that is not eating well receives less dietary potassium to begin with.

Several other factors can contribute or compound the problem.

Metabolic acidosis is both a consequence and a cause of low potassium. The excess acid drives potassium out of the cells and into the bloodstream, where it is then excreted by the kidneys. Polzin (2007) describes acidosis as a major risk factor for hypokalaemia in CKD cats.

Amlodipine, one of the most commonly used antihypertensives in cats, may promote potassium loss in cats with CKD. If your cat is on amlodipine, potassium should be monitored with particular care.

Hyperthyroidism and diabetes are both associated with lower potassium levels and are common comorbidities in older cats.

Hyperaldosteronism, while less common, is an important cause to rule out when potassium remains persistently low despite supplementation. Primary hyperaldosteronism involves overproduction of the hormone aldosterone, usually due to a benign adrenal tumour. The excess aldosterone drives potassium excretion and sodium retention, eventually leading to hypertension. If your cat has persistently low potassium and low magnesium alongside hypertension, ask your vet to consider an aldosterone evaluation and adrenal ultrasound.

Burmese, Bombay, and Tonkinese cats in some regions carry a genetic variant that can cause an inherited form of low potassium called Familial Episodic Hypokalaemic Polymyopathy. This typically presents in young cats under ten months of age. Genetic testing is available through UC Davis in the United States and Langford Veterinary Services in the United Kingdom.

Symptoms

Because potassium is essential for muscle and nerve function, the symptoms of low potassium are primarily muscular and neurological.

Muscle weakness in the hind limbs is the most commonly reported sign. Some cats develop a plantigrade stance, where they walk on their hocks rather than their feet. This can look alarming but usually resolves within a day or two of beginning supplementation.

Cervical ventroflexion, an inability to hold the head up properly, is a striking symptom that can appear quite suddenly. A 2025 study looking at 86 cases of cervical ventroflexion found that hypokalaemia was the cause in nearly half of them (Karpozilou et al., 2025). The good news is that it is usually fully reversible with treatment.

A stilted gait in the front legs, trembling or muscle twitching, and hoarseness of the voice are other possible signs. Some cats become constipated, develop increased night-time urination, or simply become lethargic and lose interest in food.

Twitching can be caused by a number of different problems in CKD cats, including high phosphorus, calcium imbalances, and hypertension, so it should not be assumed to indicate potassium alone.

When to Treat

Most veterinary guidelines use 3.5 mEq/L as the lower threshold of the reference range, but in CKD cats there is good reason to act earlier. Polzin (2007) found that cats with CKD can have reduced potassium inside their cells even when the blood level appears normal, because the body prioritises blood levels at the expense of cellular stores.

Current thinking among feline nephrology specialists supports supplementing any CKD cat whose potassium falls below 4.0 mEq/L, and aiming to keep it closer to the middle of the reference range rather than the bottom. Sieberg and Quimby (2020) noted that some clinicians advocate supplementation even when serum potassium is in the low-normal interval, with a target above 4.0 mEq/L.

If a cat has clinical signs of hypokalaemia, such as hind limb weakness or cervical ventroflexion, supplementation should begin promptly regardless of where exactly the number sits.

Treatment Options

For mild hypokalaemia, a therapeutic renal diet may be enough. These diets are formulated with additional potassium, and if a cat is eating well, dietary adjustment alone can sometimes bring levels back into range.

Subcutaneous fluid therapy can also help. Lactated Ringer’s solution contains potassium and provides some supplementation alongside hydration. For cats that are severely depleted, intravenous fluids with additional potassium can be administered in a hospital setting. It is worth knowing that potassium levels may dip further at the very start of IV fluid treatment before they begin to rise, as the extra fluid volume temporarily dilutes the concentration in the blood. This is normal and does not mean treatment is failing.

If dietary and fluid measures are insufficient, an oral potassium supplement is usually the next step.

Potassium Supplements

The three main types of oral potassium supplement used in cats are potassium gluconate, potassium citrate, and potassium chloride.

Potassium gluconate is the most widely used. It is the least likely to cause stomach upset and comes in tablet, powder, and gel forms. Most cats tolerate the powder or crushed tablet mixed into food better than the gel formulation. The standard starting dose is around 2 mEq twice daily for a typical adult cat, giving a daily total of 4 mEq. This dose is often expressed in milligrams of the gluconate salt rather than mEq, so it helps to know that 468 mg of potassium gluconate delivers approximately 2 mEq of elemental potassium. Common veterinary brands include RenaKare (available as tablet, powder, and gel), Potassa-Chew (a chewable option), and combination products such as Renal K+ and Kaminox that pair potassium gluconate with B vitamins.

Potassium citrate is a good choice for cats that also have metabolic acidosis, because citrate has an alkalinising effect. It is the form found in most therapeutic renal diets. Polzin (2007) recommends a dose of 40 to 60 mg per kg of body weight per day divided into two or three doses. Potassium citrate should be given at least two hours apart from any aluminium-containing phosphorus binders.

Potassium chloride is generally reserved for injection into subcutaneous fluid bags rather than oral use, because the oral form can contribute to metabolic acidosis. Injectable potassium chloride is available in a 2 mEq/mL concentration and is added to the fluid bag before administration. Adding a 10 mL vial to a 1,000 mL bag provides 20 mEq in the bag, so each 100 mL given delivers 2 mEq of potassium. Fluids prepared this way can sting at the injection site.

Potassium supplements should never be given without veterinary approval and a confirmed low reading on bloodwork. Giving potassium to a cat that does not need it can cause dangerous hyperkalaemia. Potassium must never be given to a cat that is unable to urinate.

ACE inhibitors (such as benazepril) and ARBs (such as telmisartan) can raise potassium levels, so cats on these medications need more frequent monitoring when potassium supplements are also in use.

If a cat does not respond to supplementation as expected, ask your vet to check magnesium levels. Low magnesium makes it difficult to restore potassium to a normal range, and correcting the magnesium deficiency first is often necessary before the potassium will respond.

Causes

The most important first step when facing a high potassium reading is to confirm it is real. A haemolysed blood sample or one that was not tested promptly can produce a falsely elevated result. Repeating the test with a fresh sample is worth doing before beginning treatment.

If the elevation is genuine, the underlying reason is almost always a problem with potassium excretion rather than excessive intake. In cats with very advanced CKD, the glomerular filtration rate has dropped so low that the kidneys cannot flush potassium out of the body efficiently. This is why hyperkalaemia tends to occur in IRIS Stage 4, typically when creatinine exceeds 5 mg/dL or 440 µmol/L.

An inability to urinate, whether from a urinary obstruction, kidney stones, or acute kidney injury, will cause potassium to climb rapidly because none is being excreted at all. This is a veterinary emergency.

ACE inhibitors and ARBs reduce potassium excretion as part of their mechanism of action, and while most cats on these medications do not reach dangerous levels, potassium should be checked 7 to 10 days after starting either drug class and periodically thereafter.

Metabolic acidosis can cause potassium to shift out of cells and into the bloodstream, producing an apparently elevated reading that may improve once the acidosis is treated.

Symptoms

Lethargy and weakness are the most common signs. Muscle trembling or twitching can also occur. At very high levels, typically above 7.0 mEq/L, the cardiac conduction system becomes affected and the risk of arrhythmia or cardiac arrest rises significantly. Short seizures have been reported in cats with extreme hyperkalaemia, particularly in end-stage disease.

Because lethargy and twitching can also appear in hypokalaemia, bloodwork is the only reliable way to distinguish between the two.

Treatment Options

Management of hyperkalaemia depends on how high the level is and how quickly it rose. Mild chronic elevation in a cat that is otherwise stable requires a different approach than an acute crisis.

The first step is to remove all sources of additional potassium. Oral supplements should be stopped immediately. If the cat is receiving subcutaneous fluids containing potassium, such as Lactated Ringer’s solution, switching to a potassium-free solution such as 0.9% saline is appropriate, though your vet may advise otherwise depending on the clinical context.

Correcting underlying metabolic acidosis can bring potassium readings down by moving potassium back into the cells where it belongs.

ACE inhibitors and ARBs may need to be reduced or discontinued if they are contributing to the elevation. The Merck Veterinary Manual advises considering dose adjustment or dietary change when potassium exceeds 6.5 mEq/L in a cat on an ACE inhibitor.

Fluid therapy, either increased subcutaneous volumes or intravenous fluids in a hospital, helps by improving kidney perfusion and promoting urinary potassium excretion. If the cat is producing little or no urine, a diuretic such as furosemide may be attempted to restore urine flow, though this approach is not always effective in end-stage disease.

For acute, severe hyperkalaemia, additional hospital interventions are available. Insulin administered alongside dextrose or sodium bicarbonate can drive potassium back into the cells temporarily. Albuterol, a bronchodilator, has also been used to lower potassium acutely. These measures buy time rather than resolving the underlying problem, but they may be enough to stabilise a cat while the primary cause is addressed.

A cation exchange resin called sodium polystyrene sulfonate (Kayexalate) can bind potassium in the gut so it is excreted in the stool rather than absorbed. This has been used in severe cases but carries a risk of gastrointestinal injury and requires careful monitoring with daily potassium checks.

Potassium should be included on every bloodwork panel throughout a CKD cat’s illness. Many laboratories do not measure it as part of a standard biochemistry screen, so it is worth requesting it explicitly.

For a cat that has recently been started on a potassium supplement, re-checking within 7 to 14 days helps confirm the dose is working and that levels have not overshot in either direction. Cats with severe symptoms such as widespread muscle weakness may warrant a recheck at 24 to 48 hours. Once a stable maintenance dose has been found, the frequency of potassium monitoring can return to whatever schedule is appropriate for the cat’s IRIS stage.

Cats on ACE inhibitors or ARBs should have potassium and kidney values checked 7 to 10 days after starting the medication and at any dose change.

What potassium level should I be aiming for in my cat with CKD? Most laboratory reference ranges list 3.5 to 5.5 mEq/L as normal, but for cats with CKD the target is closer to 4.0 to 4.4 mEq/L. A result that sits at the lower end of the normal range is worth discussing with your vet, particularly if your cat has any clinical signs.

My cat’s potassium reading came back high, should I be worried? Not necessarily right away. A haemolysed blood sample or one that was not tested promptly can produce a falsely elevated result. Repeating the test with a fresh sample is the sensible first step before making any treatment changes.

How quickly does potassium supplementation work? Most cats show measurable improvement in clinical signs within one to five days of starting oral or injectable potassium supplementation. Dramatic symptoms like cervical ventroflexion and hind limb weakness can resolve within 24 to 48 hours in some cats.

Can I buy potassium supplements for my cat without a prescription? Potassium gluconate is available over the counter in many countries, including in health food shops and online. However, you should never give a potassium supplement without confirming with your vet that your cat’s potassium is actually low. Giving potassium to a cat that does not need it can cause a dangerous rise in potassium levels.

My cat is on telmisartan. Do I need to worry about potassium? Telmisartan and other ARBs can raise potassium levels as part of how they work. Your vet should recheck potassium and kidney values 7 to 10 days after starting or adjusting the dose, and periodically while your cat remains on the medication.

Does the type of potassium supplement matter? For most cats, potassium gluconate is the preferred choice because it is the least irritating to the stomach. If your cat also has metabolic acidosis, potassium citrate may be a better fit because it has an alkalinising effect. Potassium chloride in oral form is rarely used because it can worsen acidosis.

My cat’s potassium is not responding to supplements. Why? If potassium levels remain low despite regular supplementation, the most common explanation is concurrent low magnesium. The body needs adequate magnesium to retain potassium in the cells, and supplementing potassium alone will not work well if magnesium is also depleted. Ask your vet to check magnesium levels. Hyperaldosteronism is another possibility, particularly if blood pressure is also elevated.

Karpozilou A, De Stefani A & Liatis T (2025). Cervical ventroflexion in cats: 86 cases (2003-2024). Journal of Feline Medicine and Surgery 27(7).

Langston C (2008). Managing fluid and electrolyte disorders in renal failure. Veterinary Clinics of Small Animal Practice 38, pp677-697.

Lulich JP, Osborne CA, O’Brien TD & Polzin DJ (1992). Feline renal failure: questions, answers, questions. Compendium on Continuing Education for the Practising Veterinarian 14, pp127-153.

Odunayo A (2014). Management of potassium disorders. Clinician’s Brief, March 2014, pp69-72.

de Morais HA (2009). Potassium disorders in cats: myths and facts. Presentation to the World Small Animal Veterinary Association World Congress.

Polzin DJ (2007). Chronic kidney disease. Presentation to the Delaware Valley Academy of Veterinary Medicine.

Polzin DJ (2013). Evidence-based step-wise approach to managing chronic kidney disease in dogs and cats. Journal of Veterinary Emergency and Critical Care 23(2), pp205-215.

Sieberg L & Quimby J (2020). Retrospective study of the efficacy of oral potassium supplementation in cats with chronic kidney disease. Journal of Feline Medicine and Surgery 22(6), pp539-543.