Evaluation of CBC Results with Temperature Variation: Cold Agglutinin Testing Required
When CBC results show significant differences between room temperature and 37°C measurements, with stable results after repeated warming, the next appropriate step is to perform a cold agglutinin titer (option C).
Analysis of the CBC Results
The CBC results show notable differences between measurements taken at room temperature versus those taken after incubation at 37°C:
| Parameter | Room Temp | 37°C | Significance |
|---|---|---|---|
| HCT | 36.4% | 37.5% | Increased by 1.1% |
| MCHC | 39.3 g/dL | 38.9 g/dL | Decreased by 0.4 g/dL |
These findings are consistent with a cold agglutinin phenomenon, where red blood cells agglutinate at lower temperatures and separate when warmed.
Diagnostic Algorithm
Identify the pattern: The key findings include:
- Increased hematocrit after warming
- Decreased MCHC after warming
- Relatively stable WBC, RBC, and hemoglobin values
Interpret the pattern:
- Cold agglutinins cause RBC clumping at room temperature
- This falsely decreases the RBC count and increases MCHC
- Warming to 37°C dissolves these agglutinins, normalizing values
Next steps:
- Cold agglutinin titer is required to confirm the diagnosis
- Blood smear would be insufficient to quantify the phenomenon
- Releasing results without investigation would miss a clinically significant finding
- Recollection would likely show the same pattern
Evidence-Based Rationale
Guidelines recommend maintaining blood specimens at room temperature (18-22°C) for optimal analysis 1. However, when cold agglutinins are suspected, warming the specimen to 37°C is an appropriate troubleshooting step 1.
The International Society for Thrombosis and Haemostasis specifically notes that "precautions should be taken to ensure the quality of the samples as certain factors can affect testing (e.g., presence of hemolysis or bilirubin)" 1. Cold agglutinins represent one such factor that requires special consideration.
Research shows that while most CBC parameters remain stable at different temperatures, specific parameters like hematocrit can be affected by temperature variations 2, 3. When these variations follow a pattern consistent with cold agglutinins, further investigation is warranted.
Common Pitfalls to Avoid
- Don't immediately reject the specimen: While rejection might seem appropriate for abnormal results, the pattern here is consistent with a clinical condition rather than specimen error.
- Don't simply release the results: The discrepancy between room temperature and 37°C measurements indicates a clinically significant finding that requires documentation.
- Don't stop at making a blood smear: While a smear might show agglutination, quantification via cold agglutinin titer is necessary for clinical management.
Clinical Implications
Cold agglutinins can be associated with:
- Primary cold agglutinin disease
- Secondary causes including infections (Mycoplasma pneumoniae, EBV)
- Lymphoproliferative disorders
- Autoimmune conditions
Identifying this phenomenon is critical for accurate laboratory results and may reveal an underlying condition requiring clinical attention.