Effect of High WBC Count on Hemoglobin Measurement
High white blood cell (WBC) counts above the upper linear limit on automated cell counters affect hemoglobin measurement primarily by increasing sample turbidity, which falsely elevates the hemoglobin reading.
Mechanism of Interference
When WBC counts are abnormally elevated (typically ≥40.0 × 10^9/L), they significantly impact hemoglobin measurement through several mechanisms:
- Increased Turbidity: High concentrations of WBCs in the sample create additional light scattering during spectrophotometric measurement 1
- Incomplete Lysis: At extremely high WBC counts, the standard lysing reagents may be insufficient to completely lyse all WBCs
- Optical Interference: WBCs contribute to the optical density of the sample, causing falsely elevated hemoglobin readings
Evidence of Interference
Research has demonstrated a clear relationship between elevated WBC counts and hemoglobin measurement errors:
- A logarithmic linear correlation exists between hemoglobin concentration differences and WBC count when WBC ≥40.0 × 10^9/L (r=0.9526) 1
- The regression equation Y (Hb difference) = -25.09 + 21.89 × lg[WBC (× 10^9/L)] can be used to correct for this interference 1
Clinical Significance
This interference has important clinical implications:
- Patients with leukemia, severe infections, or other conditions causing leukocytosis may have falsely elevated hemoglobin readings
- Treatment decisions regarding anemia management could be compromised if hemoglobin values are inaccurate
- Automated cell counters without correction algorithms may report misleading results in patients with extreme leukocytosis
Corrective Measures
To address this interference:
- Manual Correction: Apply mathematical correction using established formulas when WBC counts exceed 40.0 × 10^9/L 1
- Sample Processing: In cases of extreme leukocytosis, removing WBCs before hemoglobin measurement provides more accurate results 1
- Alternative Methods: Consider using methods less affected by WBC interference, such as specialized hemoglobin monitoring devices 2
Common Pitfalls
- Failing to recognize that extremely high WBC counts can affect hemoglobin measurement
- Not applying appropriate corrections in patients with leukocytosis
- Misinterpreting the degree of anemia in patients with hematologic malignancies
- Overlooking the need for manual review of automated results in patients with extreme leukocytosis
The turbidity effect of high WBC counts is the primary mechanism through which hemoglobin measurements are affected, making option C the correct answer to this question.