What factors, aside from poor mixing, can interfere with manual and automated measurements of hemoglobin (Hb) concentration?

Interference Factors in Hemoglobin Concentration Measurement

The correct answer is E. All of the given answers are correct. Extremely high WBC counts, lysis-resistant RBCs, hemolyzed/lipemic/icteric plasma, and abnormal globulins all interfere with both manual and automated hemoglobin concentration measurements.

Understanding Hemoglobin Measurement Interference

Hemoglobin measurement is one of the most frequently requested laboratory tests, but its accuracy can be compromised by various factors beyond poor sample mixing. These interferences affect both manual methods (such as cyanmethemoglobin) and automated analyzers.

Extremely High WBC Counts (Leukemias)

• High white blood cell counts, particularly in leukemias, can falsely elevate hemoglobin measurements 1
• The excessive number of WBCs contributes to increased turbidity in the sample
• In automated analyzers using optical methods, WBCs can be incorrectly counted as RBCs, leading to falsely elevated calculated hematocrit and hemoglobin values 2

Lysis-Resistant RBCs

• Some RBC abnormalities (particularly hemoglobinopathies like sickle cell disease) create cells resistant to standard lysis procedures
• These cells may not fully lyse during testing, causing inaccurate hemoglobin measurements 3
• In automated analyzers, this can affect both direct hemoglobin measurement and calculated values based on RBC parameters 4

Hemolyzed, Lipemic, or Icteric Plasma

• These pre-analytical factors significantly interfere with spectrophotometric measurements:
  • Hemolysis releases free hemoglobin into plasma, falsely elevating results
  • Lipemia (high lipids) causes light scattering, affecting optical measurements
  • Icterus (high bilirubin) can interfere with absorbance readings 5
• The College of American Pathologists (CAP) and Clinical Laboratory Improvement Amendments (CLIA) recognize these as significant interferences 1
• Laboratories should establish protocols to identify and flag samples with these interferences 5

Abnormal Globulins (Cryoglobulins)

• Abnormal proteins like cryoglobulins can precipitate during testing
• These precipitates increase sample turbidity, affecting spectrophotometric measurements
• They can also interfere with cell counting and sizing in automated analyzers 4

Best Practices for Accurate Hemoglobin Measurement

1. Sample Collection and Handling:

   • Use proper anticoagulants as specified by the assay method
   • Process samples promptly (within 1 hour if possible)
   • Maintain appropriate storage temperatures 4

2. Sample Quality Assessment:

   • Visually inspect samples for hemolysis, lipemia, and icterus
   • Use automated indices (H-, I-, and L-indices) when available 5
   • Consider alternative sampling methods for patients with known interferences

3. Method Selection:

   • For patients with known interferences, select appropriate alternative methods
   • Consider arterial or venous whole blood sampling instead of capillary methods for critically ill patients 4
   • Be aware of the specific limitations of your laboratory's analyzer 2

4. Result Interpretation:

   • Consider clinical context when interpreting results with potential interferences
   • Flag results with significant interferences that could affect clinical decisions
   • When necessary, use alternative methods to confirm questionable results

Special Considerations

• In patients with hemoglobinopathies, certain hemoglobin measurement methods may be more reliable than others 4
• For patients with kidney disease, liver disease, or other conditions affecting RBC lifespan, hemoglobin measurements may require special interpretation 4
• Modern automated analyzers have varying capabilities to detect and correct for interferences 1

Understanding these interference factors is crucial for laboratory professionals and clinicians to ensure accurate hemoglobin measurement and appropriate clinical decision-making.