Moderate severity
Hypokalaemia (Low Blood Potassium)
A potassium deficiency that leaves a cat weak and floppy — most famously causing the drooping, ventroflexed neck posture seen in some cats with kidney disease.
⚠️ Common symptoms
Potassium is the main electrolyte inside cells, and muscle and nerve tissue depend on it working properly. When blood potassium falls, the most visible casualty is skeletal muscle — and in cats that produces one of the most distinctive postures in feline medicine: ventroflexion of the neck, in which the cat sits with its chin tucked towards its chest, apparently unable to lift its head normally.
The commonest setting is chronic kidney disease. Damaged kidneys are poor at conserving potassium, so it leaks steadily into the urine while a nauseous, poorly-eating cat takes in less than it needs. The result creeps up gradually: a cat that stops jumping onto the windowsill, walks stiffly, seems tired, and eventually starts holding its head low. Because these look like the ordinary decline of an old cat, hypokalaemia is often mistaken for 'just ageing' until a blood test finds it.
Other routes to the same place include days of vomiting or diarrhoea, diabetic ketoacidosis and its treatment, and the uncommon but important hyperaldosteronism, in which an adrenal tumour drives both potassium loss and high blood pressure — a combination worth suspecting in an older cat with weakness and hypertension together.
The satisfying part is the response to treatment. Correcting potassium, cautiously and with monitoring, frequently transforms a cat within a day or two: the head comes up, the stiffness eases, and appetite improves. Intravenous potassium must be given slowly, because too-rapid correction is itself dangerous, but oral supplements are straightforward to continue at home and many cats with kidney disease stay on them long-term.
For owners of cats with kidney disease, the practical takeaway is simple: mention new weakness or a low-held head to your vet, and make sure potassium is on the list at every blood check.
🔍 Causes
Potassium is lost faster than it is replaced. In chronic kidney disease the damaged kidneys leak potassium into the urine; prolonged vomiting, diarrhoea or poor appetite reduce intake; diabetes and its treatment shift potassium into cells; and rarer conditions such as hyperaldosteronism (Conn's syndrome) drive heavy renal losses. Some older commercial diets low in potassium also contributed historically, which is why modern renal diets are supplemented.
🛡 Prevention
It cannot always be prevented, but it can be caught early. Cats with chronic kidney disease should have their blood potassium checked at every routine review, and be fed a good-quality veterinary renal diet with appropriate potassium supplementation. Encouraging fluid intake, treating vomiting and diarrhoea quickly, and never letting an unwell cat go days without eating all reduce the risk.
💊 Treatment
Treatment is potassium supplementation, given by mouth as a gel or powder for mild cases and intravenously, slowly and with close monitoring, for severe ones. Because hypokalaemia is almost always secondary to something else, the underlying cause must be treated too — most often chronic kidney disease, but sometimes prolonged vomiting or diarrhoea, diabetes, or an aldosterone-producing adrenal tumour. Muscle strength usually improves strikingly within a day or two of correcting the deficit.
⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.