High potassium — hyperkalemia — is one of the most common (and most concerning) findings on a kidney patient's lab report. The good news: most of the time, it's caused by something specific that can be identified and adjusted.
The bad news: very high potassium is genuinely dangerous. It can affect your heart rhythm and, in extreme cases, cause cardiac arrest. So this isn't something to wait on. If your potassium is above 5.5 mmol/L, contact your care team this week. If it's above 6.0, contact them today.
Potassium is measured in mmol/L (millimoles per litre) on most South African and European labs. The general ranges:
| Range | What it means |
|---|
| 3.5 - 5.0 mmol/L | Normal |
| 5.1 - 5.5 mmol/L | Mildly elevated — investigate |
| 5.6 - 6.0 mmol/L | Moderate hyperkalemia — needs attention |
| 6.0+ mmol/L | Severe — medical urgency |
For kidney patients specifically, doctors often want to keep potassium under 5.0 — tighter than the standard reference range — because the heart-rhythm risks are higher when kidneys are damaged.
This is the biggest one and the most fixable. Common culprits in the days before a high reading:
- Bananas, oranges, kiwis (fruits)
- Tomatoes, potatoes, sweet potatoes, spinach, beans (vegetables)
- Avocado (dense potassium)
- Coconut water (extremely high)
- Salt substitutes (LoSalt, NoSalt, "lite salt") — these often replace sodium with potassium chloride, dangerous for kidney patients
- Beef and pork (especially in large portions)
- Dairy in large amounts
If you logged any of these in the 24-48 hours before your blood draw, that's likely your answer.
Many processed foods and protein bars now use potassium chloride as a salt substitute. It's labeled in the ingredients but most people don't notice.
Common hidden sources:
- "Reduced sodium" or "low salt" canned soups
- Some "healthy" sports drinks (especially electrolyte powders)
- Salt-free seasonings
- Some ready meals
- Some "diet" or "lite" food alternatives
If you've recently switched to "low sodium" versions of foods, this could be why.
Several common medications raise potassium. Many are good for kidney patients in other ways, but they need monitoring:
- ACE inhibitors (enalapril, lisinopril, ramipril, perindopril)
- ARBs (losartan, valsartan, telmisartan)
- Spironolactone and eplerenone (potassium-sparing diuretics)
- NSAIDs (ibuprofen, diclofenac, celecoxib)
- Trimethoprim (an antibiotic)
- Heparin
If you started a new medication in the last few weeks, mention it. Don't stop any medication on your own — your doctor will adjust the dose or switch you to an alternative.
The classic CKD reason. As kidney function drops, potassium clearance drops with it. People with eGFR below 30 are at much higher risk of hyperkalemia, and people on dialysis have day-to-day variation depending on their treatment schedule.
If you're on hemodialysis, your potassium will be highest right before treatment and lowest right after. A high pre-dialysis number is normal; a high post-dialysis number suggests the treatment isn't removing enough — your doctor may adjust the dialysate.
This sounds strange but it's real. Your gut excretes some potassium normally. When you're constipated, that excretion drops and potassium builds up.
Constipation is very common in kidney patients (low fluid intake + high binders + reduced activity). Treating constipation can lower potassium by 0.2-0.4 mmol/L on its own.
Lab errors happen more often than you'd think. Specific causes:
- Hemolysis (red blood cells broken during the draw — common with hard pulls, small needles, or shaken samples). This releases potassium from inside cells and falsely raises the result. Lab usually flags this with a comment.
- Sample sat too long before being processed. Same effect.
- You clenched your fist hard during the draw. Repeated clenching can spike potassium temporarily.
If your potassium is suddenly very high but you feel fine and nothing in your diet or meds explains it, ask your doctor whether the sample might have been hemolyzed. A repeat test sometimes shows a much lower number.
When kidney disease is advanced, your body can't clear acid as well. The acid pushes potassium out of cells into the blood, raising the lab reading.
This is checked by another blood marker called bicarbonate (or "HCO3" or "CO2 total" on labs). If yours is below 22, you may have CKD-related acidosis, and treating that often lowers potassium too.
In rough order of priority:
Immediately if above 6.0:
- Call your nephrologist or go to an emergency department
- Don't drive yourself if you have any symptoms (palpitations, weakness, numb extremities)
This week if above 5.5:
- Stop any salt substitutes containing potassium chloride
- Cut out the obvious high-potassium foods (bananas, oranges, tomatoes, potatoes) for a few days
- Check your medication list and bring it to your next appointment
- Schedule a repeat test in 1-2 weeks
- If you're constipated, address it (more fibre within your diet, gentle movement, talk to your doctor about a kidney-safe laxative)
Ongoing if mildly above range:
- Track your daily potassium intake (DuoBean does this automatically when you log meals)
- Keep an eye on hidden sources — read ingredient lists for potassium chloride
- Make sure you're emptying your bowels regularly
- Discuss with your nephrologist whether a potassium binder (patiromer, sodium zirconium cyclosilicate) might help — these medications bind potassium in your gut so it leaves your body in stool
- Don't suddenly stop your blood pressure medication to try to lower potassium. Uncontrolled blood pressure is more dangerous than mild hyperkalemia. Your doctor will adjust the medication if needed.
- Don't take random "potassium-lowering" supplements sold online. They often don't work and some interfere with prescribed medications.
- Don't fast or skip meals before your blood test thinking it will give a "better" number. It can actually raise potassium because of muscle breakdown.
When you see them about a high potassium result:
- Could any of my current medications be raising it?
- Is my bicarbonate level normal, or might I have acidosis?
- Should I see a renal dietitian to review my food choices?
- Do I need a potassium binder?
- When should we recheck the level?
The bigger picture: A single high potassium result is rarely the end of the world, but it's a signal worth taking seriously. Most of the time, identifying the cause, diet, meds, constipation, sample handling — solves the problem. The patients who get into trouble are usually the ones who ignore repeated high readings.
Want to know exactly how much potassium you're eating each day so you can spot the pattern? DuoBean tracks every food, every drink, every sneaky source, and shows you the daily total in real time.