Hemolyzed Specimens for Electrolytes and Ammonia Testing
Hemolyzed specimens should not be used for electrolyte or ammonia testing as they can produce unreliable and potentially harmful results that may negatively impact patient care. 1
Impact of Hemolysis on Laboratory Results
Hemolysis (breakdown of red blood cells) significantly affects specimen quality and is a primary cause of unusable specimens for clinical assays. When red blood cells rupture, their intracellular contents leak into the serum or plasma, interfering with accurate measurement of several analytes:
Electrolytes
- Potassium: Significantly elevated in hemolyzed samples due to high intracellular potassium concentration
- Other electrolytes: May show variable interference depending on degree of hemolysis
Ammonia
- Hemolysis causes falsely elevated ammonia levels as intracellular contents contaminate the specimen 2
- Ammonia concentrations can more than double under certain conditions of hemolysis
Laboratory Guidelines for Specimen Handling
According to CDC guidelines, laboratories should have clear written criteria for acceptance and rejection of specimens, including determination of whether specific variances in specimen conditions (e.g., hemolyzed specimens) meet acceptance criteria 1. These guidelines state:
- Laboratories should determine which tests can be performed with compromised specimens
- If accepting specimens that deviate from established criteria, laboratories must have documentation from scientific literature or internal data proving that test performance will not be compromised
Specimen Rejection Criteria
Specimens should be rejected when:
- Blood is hemolyzed or frozen 1
- Specimen shows signs of deterioration or contamination that might affect test results 1
- The degree of hemolysis exceeds clinically significant bias thresholds 3
Special Considerations for Ammonia Testing
For ammonia testing specifically:
- Nonhemolyzed plasma specimens are essential 2
- Prompt centrifugation, separation of plasma, and determination are critical
- Duration of contact between plasma and cells is the most important factor affecting results
- Lower temperatures have minimal effect on whole-blood storage but can retard increases in ammonia in stored plasma
Clinical Impact of Specimen Rejection
While rejecting hemolyzed specimens is standard practice, there are important considerations:
- Automatic rejection of all hemolyzed specimens may delay critical results and potentially compromise patient safety 4, 5
- In some cases, the clinical urgency may outweigh the analytical concerns
Recommended Approach for Handling Hemolyzed Specimens
A pragmatic approach for managing hemolyzed specimens includes:
- Measure the hemolysis index (H-index) to quantify the degree of hemolysis
- Apply decision rules based on H-index values:
- If H-index does not generate analytically significant bias: Release results
- If H-index causes variation between analytically and clinically significant bias: Release results with a comment describing potential direction of alteration
- If H-index causes variation exceeding clinically significant bias: Suppress results and request new specimen
- If H-index is extremely high (≥10 g/L cell-free hemoglobin): Suppress all laboratory data and request new specimen 3
Pitfalls to Avoid
- Using corrective formulas: Due to inaccuracy and imprecision, using formulas to adjust results from hemolyzed specimens is discouraged 3
- Blind adherence to rejection policies: Consider clinical context before rejecting specimens, especially in emergency situations 5
- Poor communication: Ensure proper communication between laboratory and clinical staff regarding specimen rejection and the need for recollection
In conclusion, while hemolyzed specimens should generally not be used for electrolyte or ammonia testing due to potential inaccuracies, laboratories should implement a systematic approach that balances analytical quality with clinical urgency to ensure patient safety.