Will a hemolyzed blood sample of potassium give a false high or false low reading?

Hemolyzed Blood Samples Result in Falsely Elevated Potassium Readings

Hemolyzed blood samples will give a false high (elevated) potassium reading, not a false low reading. This occurs because potassium is primarily an intracellular ion, with concentrations inside red blood cells approximately 40 times higher than in plasma.

Mechanism of False Elevation

When red blood cells rupture during hemolysis, they release their intracellular contents, including potassium, into the surrounding plasma. This artificially increases the measured potassium concentration and does not reflect the patient's true in vivo potassium level 1.

The magnitude of this false elevation depends on several factors:

• Degree of hemolysis (more hemolysis = greater elevation)
• Patient's hematocrit and red blood cell count
• Time between collection and analysis
• Sample handling and processing conditions

Detection of Hemolysis

Hemolysis can be detected through:

1. Visual inspection - hemolyzed samples appear pink to red due to released hemoglobin
2. Laboratory hemolysis index (HI) - automated measurement of free hemoglobin in plasma
3. Comparison with other laboratory values that may be affected by hemolysis

Clinical Implications

This false elevation has significant clinical implications:

• May lead to incorrect diagnosis of hyperkalemia when potassium is actually normal (pseudohyperkalemia)
• May mask true hypokalemia by falsely elevating a low potassium level to normal range (pseudonormokalemia) 2
• Could result in unnecessary and potentially harmful treatment for hyperkalemia
• May delay appropriate treatment for hypokalemia

Management of Hemolyzed Samples

When a hemolyzed sample with elevated potassium is encountered:

1. Recognize the hemolysis - Laboratory reports typically flag hemolyzed samples
2. Consider recollection - A new, properly collected sample is the most reliable solution 3
3. Use correction equations with caution - Some laboratories use formulas to estimate true potassium levels based on the degree of hemolysis, but these have limitations 4, 5
4. Clinical correlation - Consider the patient's clinical status, ECG findings, and other laboratory values

Preventing Hemolysis During Collection

To minimize hemolysis during blood collection:

• Use appropriate needle gauge (larger bore when possible)
• Avoid excessive vacuum or suction during collection
• Ensure gentle mixing of samples
• Avoid prolonged use of tourniquets
• Process samples promptly
• Avoid temperature extremes during transport

Special Considerations

Several factors can affect potassium measurements beyond hemolysis:

• Platelet and leukocyte counts - High counts can release potassium during clotting 1
• Sample type - Serum vs. plasma differences
• Collection technique - Arterial, venous, or capillary samples may vary
• Patient factors - Certain medications or conditions may affect results

Conclusion

Hemolysis is one of the most common preanalytical errors affecting laboratory results. Understanding that hemolyzed samples produce falsely elevated potassium values is crucial for proper clinical interpretation and patient management. When hemolysis is detected, recollection of the sample is generally the most reliable approach to obtain an accurate potassium measurement.