Potassium is essential — it keeps your heart rhythm steady and your muscles working — but if your kidneys cannot clear it efficiently, blood levels can rise to dangerous heights. Here is what the NHS, the UK Kidney Association and the BDA say about managing potassium in CKD.
Who actually needs to restrict potassium?
Contrary to popular belief, most people with early CKD do not need a low-potassium diet. Restriction is recommended only when blood potassium starts to climb above the laboratory reference range, usually in CKD stages 4–5 or in people on certain medicines (such as ACE inhibitors, ARBs or potassium-sparing diuretics).
UK laboratory reference points
Most NHS labs report serum potassium in mmol/L. A typical normal range is 3.5–5.0 mmol/L. Renal teams usually act when levels exceed roughly 5.5 mmol/L, with urgent attention above 6.0 mmol/L.
Higher-potassium foods to be aware of
- Potatoes, sweet potatoes and chips
- Bananas, oranges, kiwi, dried fruit and avocado
- Tomato-based sauces and tomato juice
- Spinach, mushrooms and beetroot
- Chocolate, nuts, seeds and pulses
- Salt substitutes containing potassium chloride (e.g. some "LoSalt" type products)
Cooking tricks renal dietitians use
Boiling reduces the potassium content of vegetables. Peeling potatoes, cutting them into small cubes and boiling in plenty of water (which is then discarded) can cut their potassium content by around half. Avoid steaming, microwaving in their skins, or using the cooking water in soups and stews.
What about salt substitutes?
Salt substitutes that swap sodium for potassium chloride are widely sold in the UK. They are not safe for people on a potassium restriction or on potassium-sparing medication. Always check the label.
When to seek urgent help
Symptoms of dangerously high potassium (hyperkalaemia) include muscle weakness, tingling, palpitations and feeling unwell. Contact NHS 111, your renal team, or in severe cases call 999.