Potassium Measurement: ABG vs Peripheral Blood Draw
For potassium measurement, both arterial blood gas (ABG) analyzers and peripheral venous blood draws sent to the laboratory are sufficiently accurate for clinical decision-making, with ABG offering the critical advantage of results within 5 minutes versus 30 minutes for laboratory analysis. 1
Evidence for Accuracy and Agreement
The available evidence demonstrates acceptable agreement between ABG and laboratory measurements of potassium, with biases that do not exceed clinically significant thresholds:
A 2022 study of 265 patients found that more than 95% of potassium measurements fell within ±2 standard deviations of the mean difference between ABG and laboratory methods, with a bias of only 0.19 mmol/L and Lin's concordance correlation coefficient of 0.6584 1
A 2008 study of 529 paired arterial samples showed a mean difference of only 0.03 mmol/L (95% CI 0.011 to 0.056) between ABG and laboratory measurements, with 95% of results falling within difference limits of 0.5 mmol/L 2
A 2009 study of 200 paired samples found no significant difference between ABG potassium (mean 3.74, SD 1.92) and laboratory potassium (mean 3.896, SD 1.848), with p = 0.2679 3
A 2015 study of 200 patients demonstrated that although statistical differences existed between ABG and laboratory potassium measurements, the biases did not exceed USCLIA-determined limits, making ABG measurements reliable for clinical use 4
Clinical Decision-Making Algorithm
When potassium measurement is needed urgently (within 5-10 minutes), use ABG analyzer results to guide immediate clinical decisions in the following situations:
- Diabetic ketoacidosis before initiating insulin infusion 1
- During cardiopulmonary resuscitation 1
- Severe hypokalemia requiring urgent replacement 1
- Management of hyperkalemia 1
- Critically ill patients in shock, on vasopressor therapy, or with severe peripheral edema 5
When time permits (>30 minutes) and the clinical situation is less urgent, peripheral venous blood draw to the laboratory remains the standard reference method.
Important Technical Considerations
For arterial sampling, proper technique is essential to avoid contamination errors:
- Samples from arterial sites are most similar to laboratory plasma or blood gas analyzer values in paired samples 5
- When using venous specimens, take care to avoid contamination from IV fluid infusing through a multilumen catheter 5
- Establish a sampling site hierarchy that prioritizes arterial or venous sampling over capillary sampling in critically ill patients 5
Avoid arterial line flush contamination, which can cause falsely low glucose readings (though this primarily affects glucose, not potassium): 5
- Use only sodium chloride 0.9% (with or without heparin) for arterial line flush 5
- Properly discard dead space volume before drawing the sample 5
Clinician Practice Patterns
Despite the evidence supporting ABG accuracy, clinical practice remains divided:
- A 2008 survey found that 51.6% of doctors would wait for laboratory confirmation while 48.4% would base clinical decisions on ABG results 2
- This hesitation persists despite evidence showing sufficient agreement for effective clinical decision-making 2
Common Pitfalls to Avoid
Do not delay urgent treatment waiting for laboratory confirmation when ABG potassium is available and clinically appropriate - the 25-minute time difference can be critical in emergencies like DKA or cardiac arrest 1
Be aware that some studies show conflicting results - a 2012 study found unacceptable inter-analyzer agreement with biases of 0.150-0.352 mmol/L 6, suggesting that concordance should be established for your specific ABG system before relying on it for critical decisions 6
Recognize that sodium measurements show less agreement between ABG and laboratory methods - multiple studies demonstrate significant differences in sodium values, so laboratory confirmation is more important for sodium than potassium 3, 4, 6