A potassium of 5.2 mmol/L should be repeated in primary care, as this level meets the threshold for hyperkalaemia and requires confirmation to exclude pseudohyperkalaemia and guide management.
Why Repeat Testing is Essential
The test must be repeated because a single elevated potassium reading of 5.2 mmol/L cannot distinguish between true hyperkalaemia and pseudohyperkalaemia, and this distinction is critical for patient safety. According to the most recent 2025 European guidelines, hyperkalaemia is defined as potassium >5.0 mmol/L, and importantly, adverse outcomes can manifest even at levels of 5.1-5.4 mmol/L in patients with cardiorenal disease 1. Your patient's value of 5.2 mmol/L falls directly within this concerning range.
The Pseudohyperkalaemia Problem
Pseudohyperkalaemia is extremely common in primary care settings. Research shows that 86.4% of elevated potassium results in primary care turn out to be false elevations when properly retested 2. This occurs because:
- Primary care samples have longer transport times at ambient temperatures
- Delayed laboratory processing causes potassium to leak from cells into serum
- Cold weather dramatically worsens this problem—one study found 82.4% of critical hyperkalaemia results in November were pseudohyperkalaemia versus only 41.2% in August 3
- Processing delays of 50 minutes or more significantly increase false readings 2
How to Repeat the Test Properly
To get an accurate result:
- Repeat within 7 days to confirm the finding
- Ensure the sample is processed quickly (ideally <30 minutes)
- Check for haemolysis on the laboratory report—this invalidates the result
- If possible, have the patient go directly to the laboratory rather than using courier transport
- Consider requesting the laboratory note the processing time
What to Assess While Awaiting Repeat Results
Before the repeat test, evaluate:
- Medications: ACE inhibitors, ARBs, spironolactone, NSAIDs, trimethoprim—all cause true hyperkalaemia 4
- Renal function: Check eGFR. If eGFR ≥60 mL/min/1.73m², the likelihood of true hyperkalaemia is lower 2, 5
- Symptoms: True hyperkalaemia is usually asymptomatic until severe, but check for muscle weakness or palpitations
- ECG changes: If the patient is symptomatic or potassium was >6.0 mmol/L, obtain an ECG. A normal ECG with eGFR ≥60 has 100% negative predictive value for true hyperkalaemia 5
Clinical Context Matters
The 2018 European Society of Cardiology guidelines classify 5.2 mmol/L as mild hyperkalaemia (>5.0 to <5.5 mmol/L) 4. However, this classification assumes the result is accurate. The guidelines emphasize that chronic or recurrent hyperkalaemia is defined as potassium >5.0 mmol/L measured repetitively over a 1-year period 4—meaning a single reading doesn't establish a diagnosis.
When NOT to Repeat (Rare Exceptions)
The only scenario where you might not repeat is if:
- The patient has advanced CKD (eGFR <30), heart failure, or diabetes
- They're on multiple RAASi medications
- Previous potassium levels have been consistently elevated
- The clinical context strongly suggests true hyperkalaemia
Even then, confirming with proper sampling technique is prudent.
What Happens After Confirmation
If the repeat test confirms true hyperkalaemia (>5.0 mmol/L):
- Do not automatically stop RAASi therapy—this increases mortality 1
- Identify and correct reversible causes first (NSAIDs, dietary potassium, dehydration) 1
- Consider potassium binders to maintain RAASi therapy rather than discontinuing life-saving medications 1
- Establish regular monitoring if the patient has risk factors for recurrence
Common Pitfall to Avoid
The biggest mistake is treating or modifying medications based on a single elevated result without confirmation. Studies show that even with documented hyperkalaemia, only 2% of cases receive a formal diagnosis in primary care, and management is often suboptimal 6. Don't contribute to this by either over-treating pseudohyperkalaemia or under-recognizing true hyperkalaemia.