Potassium — dangerous high and low
Potassium is very nearly the only CKD marker that is dangerous in both directions. Creatinine is a problem when high, HCT is a problem when low — but potassium stops a cat walking when it's low and stops the heart when it's high.
And because the responses are opposites, acting without knowing the direction makes things worse. This article exists to help you find that direction.
Both potassium supplementation and hyperkalemia treatment are decided on bloodwork, with your vet. Giving potassium on a guess is dangerous.
1. What potassium does
Potassium is a mineral that lives inside cells. 98% of the body's potassium is intracellular, and what a blood test shows is the 2% outside. That single fact is the key to this whole article.
The difference in concentration across the cell membrane generates electricity. So when potassium shifts, the electrical things fail first.
- Muscle — walking, jumping, holding the head up
- Heart — the heart is a muscle that beats on electricity. Potassium abnormalities show up directly in rhythm
- Nerves — sensation and reflexes
- Gut motility — low potassium brings constipation
2. Why potassium falls in CKD
Low potassium is the more common problem in CKD, especially early to mid stage. There are several reasons and they usually stack.
- It leaks out in urine — the kidney can't concentrate, volume rises, and potassium goes with it. This is the biggest reason
- She eats less — a poor appetite cuts intake first
- Vomiting — it leaves along with digestive fluids
- Hormones — the RAAS axis, activated as kidneys decline, increases potassium excretion
- Diuretics — drugs like furosemide push potassium out too
Low potassium damages the kidneys by itself. Deficiency injures kidney tissue, and injured kidneys leak more potassium.
It's a loop, so when it's low, don't leave it — correct it.
3. And why it rises
High potassium generally comes later, or alongside a specific circumstance.
- When urine output drops — end stage, or acute decompensation. Block the exit and it accumulates
- Urinary obstruction — stones, urethral blockage. An emergency, especially in males
- Metabolic acidosis — when the body turns acidic, potassium is pushed out of cells. Covered in detail in section 7
- Medications — ACE inhibitors (benazepril and others), ARBs (telmisartan), and spironolactone all push potassium up
- Dehydration — concentrated blood and reduced renal flow mean less excretion
Lab artefact can also read high. Red cells rupturing during collection (hemolysis), a sample left too long, or — in cats — platelet clumping can all raise the measured value.
If the number is high with no symptoms at all, it's worth asking to repeat it.
4. What you can see at home
| Low potassium | High potassium |
|---|---|
|
Head drops downward — a distinctly hunched, head-down posture. The most characteristic sign of hypokalemia Weak, wobbly hind legs Walking poorly, avoiding jumps Lethargy · poor appetite Constipation Drinking more, urinating more |
Almost no symptoms early on — which is exactly what makes it dangerous Lethargy · flatness Muscle weakness Slowed heart rate Collapse In severe cases arrhythmia and cardiac arrest |
A downward-dropped head posture strongly suggests hypokalemia. Film it and show your vet.
Hyperkalemia is silent until it suddenly isn't. There is no way to know without testing — regular bloodwork is the only method.
Hyperkalemia is silent until it suddenly isn't. There is no way to know without testing — regular bloodwork is the only method.
5. What to look at on the blood test
Never potassium alone. The values around it tell you the cause.
| Value | What it tells you |
|---|---|
| K (potassium) | The value itself — read with the lab's printed reference range |
| Na · Cl | Chloride rising alongside is a clue pointing to acidosis |
| Na/K ratio | Low sodium with high potassium suggests adrenal disease (Addison's). Rare in cats |
| tCO₂ · HCO₃ | Looks at acidosis directly. Below 16 warrants correcting |
| BUN / creatinine ratio | A sudden spike in this ratio points toward dehydration or acidosis |
| Phosphorus · calcium | Electrolytes move together |
| Magnesium | Important. If magnesium is low, potassium will not rise no matter how much you supplement |
If you're supplementing potassium and it won't come up, check magnesium. Without enough magnesium, cells cannot hold onto potassium.
Missing this combination costs some people months.
6. What to look at on the urine test
If blood says "how much right now," urine says "why."
- Specific gravity (USG) — how well urine is being concentrated. The more dilute, the more potassium leaves with it
- Urine pH — leaning acidic (5.0–5.5) is a clue to systemic acidosis
- Proteinuria (UPC) — often worsens in parallel, so look together
- Infection — a urinary tract infection destabilises kidney status
- Fractional excretion of potassium (FEK) — separates "leaking out" from "not taking in." Not offered everywhere
7. Metabolic acidosis and potassium — two sides of one story
This is the heart of the article. A large share of unmanageable potassium is actually acidosis.
Recall from section 1 that 98% of potassium sits inside cells. When the body turns acidic:
- Excess hydrogen ions (H⁺) move into cells
- To balance the charge, potassium (K⁺) is pushed out of cells
- Blood potassium rises — not because there is more potassium in the body, but because it has relocated
So trying to lower potassium while leaving acidosis in place doesn't work. Adding more fluid to flush it out gets you nowhere. Fix the cause and the result follows.
If blood gas testing isn't available
Acidosis is confirmed properly on blood gas (pH, HCO₃), but many clinics don't have the analyser. In that case you can assemble indirect clues.
- Urine pH is low (acidic, 5.0–5.5)
- Chloride (Cl) is elevated
- BUN/creatinine ratio is well above its usual level
- Potassium doesn't fall even when fluids are increased
All four together point strongly toward acidosis. Confirmation is still a test, and the judgement belongs with your vet.
A real case — potassium 8.0 down to 5.3
A 15-year-old stage 3 cat developed pancreatitis, hovered around potassium 7.0, then reached 8.0. Subcutaneous 0.9% saline was increased repeatedly and potassium did not come down. At the same time: urine pH 5.0, elevated chloride, BUN/creatinine ratio 33 — the acidosis signals were all lined up.
26 days after switching the fluid to buffered Hartmann's, potassium was 5.3. Creatinine 6.0→4.2, BUN 172→118, and the BUN/creatinine ratio normalised from 33→28 alongside.
This is one case and other aspects of care changed too, so causation can't be claimed. But the direction — "don't just watch potassium, look at acidosis" — is clear.
A 15-year-old stage 3 cat developed pancreatitis, hovered around potassium 7.0, then reached 8.0. Subcutaneous 0.9% saline was increased repeatedly and potassium did not come down. At the same time: urine pH 5.0, elevated chloride, BUN/creatinine ratio 33 — the acidosis signals were all lined up.
26 days after switching the fluid to buffered Hartmann's, potassium was 5.3. Creatinine 6.0→4.2, BUN 172→118, and the BUN/creatinine ratio normalised from 33→28 alongside.
This is one case and other aspects of care changed too, so causation can't be claimed. But the direction — "don't just watch potassium, look at acidosis" — is clear.
"Potassium is high — is it really okay to give fluid that contains potassium?"
Hartmann's has about 4 mEq of potassium per litre; acetate-buffered solutions around 5 mEq. At 100–150 ml a day, the amount actually going in is under 1 mEq. Meanwhile, the potassium returning into cells as acidosis corrects is far greater. So when the direction is right, the net effect is downward. For fluid selection in detail, see the subcutaneous fluids chapter.
Hartmann's has about 4 mEq of potassium per litre; acetate-buffered solutions around 5 mEq. At 100–150 ml a day, the amount actually going in is under 1 mEq. Meanwhile, the potassium returning into cells as acidosis corrects is far greater. So when the direction is right, the net effect is downward. For fluid selection in detail, see the subcutaneous fluids chapter.
8. Which range is safe
Reference ranges differ slightly by lab. Go by the range printed on your report first; the table below is a rough orientation.
| Potassium (mmol/L) | Status | Usual response |
|---|---|---|
| < 2.5 | Severe hypokalemia — weakness that can reach the respiratory muscles | Clinic. IV replacement |
| 2.5 – 3.0 | Moderate hypokalemia | Start oral supplementation |
| 3.0 – 3.5 | Mild hypokalemia | Consider supplementing · recheck |
| 3.5 – 5.0 | Stable range | Maintain |
| 5.0 – 6.0 | Mildly elevated | Find the cause · review medications · recheck |
| 6.0 – 7.0 | Moderate — ECG changes possible | Treat actively |
| > 7.0 | Severe — bradycardia, arrhythmia, arrest risk | Emergency |
But the number alone doesn't set the risk. A 7.0 that crept up over months and a 6.5 that appeared in a day hit the body differently. Whether urine is still being produced, and whether there are symptoms, matter alongside.
9. What can be done when potassium is high
At the clinic
- IV fluids — restores circulating volume and helps excretion. The foundation
- Calcium gluconate — doesn't lower potassium but protects the heart. It buys time in the danger zone
- Dextrose ± insulin — drives potassium back into cells. Fast, but temporary
- Sodium bicarbonate — given IV when acidosis is the cause
- Relieving obstruction — if the urinary tract is blocked, that comes before anything else
At home
- Re-examine the fluid type — if you've been on plain saline for a long time, discuss switching to a buffered solution
- Review the medications — ACE inhibitors, ARBs and spironolactone raise potassium. Not a reason to stop them; a reason to know
- Check supplements for potassium — some renal supplements contain it
- Confirm urine is being produced, every day — the most important one
Sodium bicarbonate — how much, how
This corrects acidosis and sends potassium back into cells. The compound is sodium bicarbonate (NaHCO₃) — the same thing as baking soda. But baking powder will not do — it contains other ingredients.
| Item | Guide |
|---|---|
| Starting dose | Typically 8–12 mg per kg body weight, 2–3 times daily |
| For a 5 kg cat | 40–60 mg per dose, 80–180 mg daily total |
| Target | Blood bicarbonate (tCO₂ · HCO₃) of 16–24 |
| When to give | About 2 hours after eating. It neutralises stomach acid and can interfere with digestion, so keep it away from meals |
| With other medications | Space it apart from phosphate binders and similar — changing gastric pH can affect absorption |
You cannot measure this with a teaspoon.
One teaspoon of baking soda is about 4.6 g. Even 1/8 teaspoon is 570 mg — well past a 5 kg cat's entire daily dose. Eyeballing it delivers several times over.
Weigh it on a 0.01 g scale, or have a pharmacy make it up in capsules.
One teaspoon of baking soda is about 4.6 g. Even 1/8 teaspoon is 570 mg — well past a 5 kg cat's entire daily dose. Eyeballing it delivers several times over.
Weigh it on a 0.01 g scale, or have a pharmacy make it up in capsules.
Bicarbonate is a support, not a solution.
If whatever is generating the acidosis is still running, offsetting it with bicarbonate is filling a leaking bucket. In the case above, bicarbonate was given continuously and potassium still climbed to 8.0 — it only came down once the fluid was switched to a buffered one.
Before increasing bicarbonate, ask first: "what is producing this acidosis right now?"
If whatever is generating the acidosis is still running, offsetting it with bicarbonate is filling a leaking bucket. In the case above, bicarbonate was given continuously and potassium still climbed to 8.0 — it only came down once the fluid was switched to a buffered one.
Before increasing bicarbonate, ask first: "what is producing this acidosis right now?"
There are cautions. Sodium bicarbonate contains, as the name says, sodium. With hypertension or heart disease, that sodium load has to be weighed. Too much swings the other way into alkalosis, so once started, confirm the direction with a recheck.
Not urinating plus high potassium means going to the clinic now. In males especially this may be urethral obstruction, and hyperkalemia can stop the heart within hours.
10. What can be done when potassium is low
At home
- Oral potassium supplement — potassium gluconate is the most common; potassium citrate is used when acidosis is also present. Split the daily dose
- Renal prescription diet — usually potassium-enriched
- Increase intake — the root fix is eating. If she isn't eating, start there
- Check magnesium — for the reason above, if supplementing isn't working
Potassium supplements — which, and how much
Brands differ by country, so remember the compound names. Two are used orally.
| Compound | Dosing guide | For a 5 kg cat |
|---|---|---|
| Potassium gluconate The default. Reasonably palatable |
2–6 mEq daily, split into two doses | Powder and gel products are typically 1/4 teaspoon = 2 mEq. So 1/4 to 3/4 teaspoon daily, divided morning and evening |
| Potassium citrate When acidosis is also present — citrate metabolises to bicarbonate, addressing both |
40–75 mg per kg, twice daily | 200–375 mg per dose, 400–750 mg daily total |
With both, start at the low end and raise based on the recheck. Choosing products and fine-tuning will get a dedicated article.
Do not give potassium chloride (KCl) by mouth. It irritates the stomach and tastes bad; oral use means the gluconate or citrate form.
Potassium chloride is what clinics add to IV fluids.
At the clinic
- Potassium added to fluids — IV delivery has a rate limit (roughly 0.5 mEq per kg per hour or less). Too fast is itself dangerous to the heart
- Treating the cause — if there's vomiting or diarrhoea, start there
Don't start potassium supplements on your own. In CKD, potassium can be low and later become high.
Once you start, recheck in 1–2 weeks to confirm the direction is right.
11. What to ask your vet
After reading, the question left is "so what do I do today?" Here it is, phrased so you can say it as written.
When potassium is high
- "Could we also run blood gas or tCO₂ (bicarbonate)? I'd like to know whether this is acidosis"
- "She's on plain saline subcutaneously — what about switching to a buffered fluid (Hartmann's or an acetate solution)?"
- "Is anything she's taking raising her potassium?" (ACE inhibitors, ARBs, spironolactone)
- "Is she a candidate for sodium bicarbonate? If so, could you set the dose?"
- "Should we check whether urine output has dropped?"
When potassium is low
- "Can we start a potassium supplement? Please set a dose for potassium gluconate"
- "If there's acidosis too, would potassium citrate be better?"
- "Could we check magnesium as well? I read it can block correction"
- "When should we recheck?"
You don't need to ask all of them. Two or three that fit your cat right now will already change the direction of the visit.
If you've uploaded the lab report to the app, print the clinic report and bring it too.
12. When something else is layered on top
If potassium is unusually hard to control, it may not be the kidneys alone.
| What may be layered on | Effect on potassium |
|---|---|
| Urinary obstruction · stones | High potassium. An emergency |
| Pancreatitis | Destabilises via dehydration and acidosis. The whole renal panel swings with it |
| Cardiac medications | ACE inhibitors, ARBs and spironolactone raise it; diuretics lower it |
| Hyperthyroidism | Starting treatment reveals masked kidney disease and electrolytes shift |
| Diabetes | Blood potassium and total body potassium diverge. Particular care during insulin therapy |
| Hypoadrenocorticism (Addison's) | High potassium + low sodium. Rare in cats |
| Hypomagnesemia | The common hidden reason hypokalemia won't correct |
There is no single answer in CKD that fits every cat. Two cats at stage 3 differ in what hurts most and what they respond to.
Reading direction from the surrounding values beats fixating on one number — and it's faster in the end.
Upload the lab report to the app and you can see potassium and its neighbours change on one screen.
13. Related
- Subcutaneous fluids, safely at home — how fluid type acts on potassium and acidosis
- How to read kidney values on a blood test — reading the values beside potassium