Can I use an Arterial Blood Gas (ABG) sample instead of a plasma sample to diagnose pseudohyperkalemia in a patient with Chronic Kidney Disease (CKD) and diabetic nephropathy?

Can ABG Samples Replace Plasma Samples for Diagnosing Pseudohyperkalemia?

Yes, arterial blood gas (ABG) samples can effectively replace plasma samples to diagnose pseudohyperkalemia in patients with CKD and diabetic nephropathy, as arterial samples avoid the in vitro potassium release from platelets and leukocytes that occurs during venous blood clotting.

Understanding Pseudohyperkalemia in CKD Patients

Pseudohyperkalemia occurs when potassium is falsely elevated in serum due to in vitro release from blood cells during or after sample collection, rather than reflecting true elevation in the body 1, 2. This is particularly problematic in CKD patients where distinguishing true from false hyperkalemia directly impacts critical treatment decisions 3.

Key Diagnostic Principle

The fundamental difference between serum and plasma potassium measurements is that serum undergoes clotting, which allows platelets and leukocytes to release intracellular potassium, while plasma (including arterial samples) is anticoagulated and prevents this release 3, 4.

Why ABG Samples Work for Pseudohyperkalemia Diagnosis

Mechanism of Detection

• Arterial blood samples are collected in heparinized syringes and processed immediately without clotting, preventing the in vitro potassium release that causes pseudohyperkalemia 1, 5
• Plasma potassium concentrations are typically 0.1-0.4 mEq/L lower than serum levels due to platelet potassium release during coagulation 1
• Pseudohyperkalemia is formally defined as a serum-to-plasma potassium difference exceeding 0.4 mmol/L when both samples are obtained simultaneously 3, 4

Clinical Evidence

• In patients with thrombocytosis (platelet counts >500 × 10⁹/L) and CKD, serum potassium can be dramatically elevated while plasma potassium remains normal 2, 3
• One case report documented serum potassium of 8.2 mEq/L while simultaneous plasma potassium was 6.4 mEq/L in a CKD patient with polycythemia vera 6
• Patients with CKD and myeloproliferative disorders are at particularly high risk for pseudohyperkalemia, even without extreme thrombocytosis or leukocytosis 6

Practical Algorithm for Using ABG Samples

When to Suspect Pseudohyperkalemia

1. Elevated serum potassium without corresponding ECG changes (no peaked T waves, widened QRS, or other hyperkalemia findings) 1, 7
2. Platelet count >500 × 10⁹/L or white blood cell count >100 × 10⁹/L 2, 4
3. Hyperkalemia that fails to respond to standard treatments (dialysis, potassium-lowering medications) 2, 3
4. History of myeloproliferative disorders, thrombocytosis, or leukocytosis 2, 6
5. Hemolysis noted on laboratory report or prolonged tourniquet application during phlebotomy 1

Diagnostic Approach

Step 1: If pseudohyperkalemia is suspected based on above criteria, obtain an arterial blood sample (ABG) or properly collected plasma sample simultaneously with serum sample 1, 5

Step 2: Compare potassium values:

• If serum K⁺ exceeds plasma/arterial K⁺ by >0.4 mmol/L, pseudohyperkalemia is confirmed 3, 4
• If difference is ≤0.4 mmol/L, true hyperkalemia is present and requires treatment 3

Step 3: For confirmed pseudohyperkalemia, use plasma or arterial samples for all future potassium monitoring 2, 3

Critical Clinical Implications for CKD Patients

Avoiding Dangerous Overtreatment

• Treating pseudohyperkalemia as true hyperkalemia can lead to life-threatening hypokalemia from unnecessary dialysis, potassium binders, or insulin administration 2, 3
• One fatal case involved a CKD patient with essential thrombocythemia who received inappropriate hyperkalemia treatment for pseudohyperkalemia, ultimately dying from electrolyte disturbance 2
• In patients with renal disease and thrombocytosis, plasma potassium should be routinely measured before instituting aggressive therapy or altering dialysis prescription 3

KDIGO Guideline Context

The 2024 KDIGO guidelines emphasize awareness of factors influencing potassium measurement, specifically noting that "plasma versus serum samples" represent a critical variable that can affect potassium values 8. This directly supports using plasma-equivalent samples (like ABG) when pseudohyperkalemia is suspected.

Specific Recommendations for Your Patient Population

For CKD Patients with Diabetic Nephropathy

• Monitor for thrombocytosis or leukocytosis on routine complete blood counts, as these patients may develop myeloproliferative changes 6
• If serum potassium is elevated but patient is asymptomatic with normal ECG, obtain arterial or plasma sample before initiating treatment 1, 5
• Consider baseline plasma potassium measurement in all CKD patients with platelet counts >500 × 10⁹/L to establish whether pseudohyperkalemia exists 2

Monitoring Considerations

• When managing CKD patients on RAAS inhibitors or mineralocorticoid receptor antagonists, use consistent sample types (plasma vs serum) for serial monitoring 8
• Recheck potassium within 2-4 hours after emergency interventions and within 24-48 hours after medication adjustments, using the same sample type 9

Common Pitfalls to Avoid

• Never delay treatment of true severe hyperkalemia (>6.0 mEq/L with ECG changes) while waiting for plasma confirmation—clinical judgment supersedes laboratory confirmation in emergencies 9, 7
• Do not assume all elevated potassium in CKD is true hyperkalemia; pseudohyperkalemia occurs even in patients with advanced renal failure 2, 3, 6
• Avoid using fist clenching during phlebotomy or prolonged tourniquet application, as these can cause pseudohyperkalemia even with normal blood counts 1
• Do not permanently discontinue beneficial RAAS inhibitors based on a single elevated serum potassium without confirming with plasma/arterial sample 9