Can Serum Potassium Differ from VBG Potassium?
Yes, serum potassium can differ from venous blood gas (VBG) potassium measurements, and a normal VBG potassium does not rule out true hyperkalemia—you must rule out pseudohyperkalemia by repeating the measurement with proper blood sampling technique, as hemolysis or tissue breakdown during phlebotomy can falsely elevate potassium levels. 1
Understanding the Discrepancy
The key issue is pseudohyperkalemia, which occurs when:
- Hemolysis during blood collection releases intracellular potassium into the sample, artificially elevating the measured level 1
- Tissue breakdown during phlebotomy (from prolonged tourniquet time, fist clenching, or traumatic venipuncture) can falsely increase potassium readings 1
- Delayed sample processing allows red blood cells to leak potassium into the serum 1
VBG samples may be less prone to hemolysis if drawn carefully through an arterial or venous line, while peripheral venipuncture for serum chemistry is more susceptible to these technical errors.
Critical Action Steps
When faced with discordant potassium values:
- Repeat the measurement immediately with meticulous blood sampling technique to confirm whether hyperkalemia is real or artifactual 1
- Obtain an ECG immediately to assess for cardiac effects (peaked T waves, flattened P waves, prolonged PR interval, widened QRS complex) regardless of which value you trust 1
- Do not delay treatment if clinical suspicion is high and ECG changes are present—treatment should not be delayed while waiting for confirmation of repeat laboratory values 1
Common Pitfall to Avoid
The European Heart Journal warns against failing to rule out pseudohyperkalemia before initiating aggressive treatment or making medication changes 1. However, if the patient has ECG changes, symptoms (muscle weakness, paresthesias), or high-risk comorbidities (CKD, heart failure, diabetes), treat first and confirm later 1.
The bottom line: trust the clinical picture and ECG more than any single laboratory value, and always verify unexpected or discordant results with proper technique 1.