What RBC (Red Blood Cell) parameter is most likely to indicate possible interference from a lipemic sample on automated cell counters?

Mean Corpuscular Hemoglobin Concentration (MCHC) is the Most Likely RBC Parameter to Indicate Lipemic Interference

The most likely calculated RBC parameter that would alert you to possible interference from a lipemic sample on virtually all automated cell counters is the Mean Corpuscular Hemoglobin Concentration (MCHC).

How Lipemic Samples Affect Automated Cell Counters

Automated hematology analyzers calculate hematocrit using the formula:

• Hematocrit = RBC count × MCV 1

When a blood sample contains excessive lipids (lipemia), this creates several measurement issues:

1. Direct effect on MCV measurement: Lipemic samples can cause falsely elevated MCV readings due to interference with the optical or impedance methods used by cell counters.

2. Calculated hematocrit distortion: Since hematocrit is calculated using MCV (Hct = RBC × MCV), any error in MCV measurement will propagate to the hematocrit value.

3. MCHC calculation impact: MCHC is calculated as Hemoglobin ÷ Hematocrit. When hematocrit is falsely elevated due to lipemia, the MCHC becomes falsely decreased.

Why MCHC is the Key Indicator

MCHC serves as the most reliable indicator of lipemic interference for several reasons:

• Sensitivity to interference: MCHC is particularly sensitive to lipemic interference because it's a calculated parameter dependent on both hemoglobin and hematocrit measurements 2.

• Distinctive pattern: Lipemic samples typically produce a characteristic pattern of falsely elevated MCV and hematocrit with falsely decreased MCHC.

• Built-in quality check: Most modern analyzers have flags or alerts when MCHC falls below physiologically possible values (typically <300 g/L), making it an effective screening tool for sample integrity 3.

Other RBC Parameters Affected by Lipemia

While MCHC is the primary indicator, other parameters can also be affected:

• MCV: May be falsely elevated in lipemic samples, but this elevation alone is less specific for lipemia as it can occur with numerous other conditions 4.

• Hemoglobin: Generally less affected by lipemia than calculated parameters, as most modern analyzers use methods that are relatively resistant to lipemic interference 5.

• RBC count: May be affected to a lesser degree, depending on the analyzer technology.

Recognizing and Managing Lipemic Interference

When lipemic interference is suspected:

1. Visual inspection: Examine the sample for milky appearance.

2. Review flagged results: Pay attention to analyzer flags indicating turbidity or lipemia.

3. Check for physiologically impossible values: MCHC values below the physiological minimum (approximately 300 g/L) should raise immediate suspicion.

4. Confirm with other parameters: Elevated triglycerides or cholesterol can support the diagnosis of lipemia.

5. Sample processing options: Ultracentrifugation can effectively remove lipemic interference for many laboratory tests 6.

Clinical Implications

Recognizing lipemic interference is critical because:

• It can lead to misdiagnosis if not identified
• It may necessitate recollection of samples after fasting
• It can affect multiple laboratory parameters beyond the CBC

By monitoring MCHC as the primary indicator of lipemic interference, laboratory professionals can quickly identify potentially inaccurate results and take appropriate steps to obtain reliable measurements.