Reasons for MCV Delta Failure
MCV delta failures occur most commonly due to blood sample mislabeling, recent blood transfusions, and bone marrow transplantation.
Understanding MCV Delta Checks
Mean Corpuscular Volume (MCV) delta checks are quality control tools used in laboratory medicine to compare current blood test results with previous results from the same patient. A significant unexplained change in MCV between sequential samples may indicate a potential error.
What is an MCV Delta Failure?
- A delta check failure occurs when there is an unexpected significant change in MCV between two sequential samples from the same patient
- Typically defined as an MCV change of >3.0 fL in a short time period 1
- Some studies use a threshold of ≥10 fL within less than 30 days 2
Top Causes of MCV Delta Failures
1. Preanalytical Errors
- Sample mislabeling: The most common cause of delta check failures
- Wrong blood in tube (WBIT) errors account for approximately 65% of failed delta checks 3
- Occurs when blood is drawn from one patient but labeled with another patient's information
- Critical patient safety issue that could lead to mismatched transfusions
2. Recent Medical Interventions
Blood transfusions: A major cause of legitimate MCV changes
- 27 out of 38 patients (71%) with MCV changes ≥10 fL had received blood transfusions within the previous 2 months 2
- Donor red cells may have different MCV than recipient's native cells
- Effect can persist for weeks depending on the lifespan of transfused cells
Bone marrow transplantation:
- Accounts for 16% of significant MCV changes in hematology patients 2
- New donor stem cells produce red blood cells with potentially different characteristics
- MCV changes can be substantial as donor cells replace recipient cells
3. Pathophysiological Changes
Rapid onset of iron deficiency or repletion:
- Iron deficiency leads to microcytosis (decreased MCV) 4
- Rapid iron repletion therapy can cause significant MCV increases
Acute disease processes:
Clinical Implications
Detection of Errors
- Implementation of logical delta checks has been shown to identify preanalytic and analytic specimen problems that might otherwise be missed 1
- MCV delta checks alone have limited sensitivity, identifying only 3 of 6 confessed mislabeled specimens in one study 1
- Composite CBC delta (CCD) checks that include multiple parameters are more effective at identifying errors 1
Patient Safety
- Delta check failures should trigger immediate investigation before results are reported
- Failed delta checks have prevented accidental mismatched blood transfusions 3
- Implementation of delta checks requiring immediate verbal feedback to caregivers was associated with more retracted erroneous results 1
Practical Approach to MCV Delta Failures
Verify patient identity:
- Confirm patient identification on current and previous samples
- Check for possible sample mix-ups or mislabeling
Review medical history:
- Check for recent blood transfusions or bone marrow transplantation
- Review medication changes, especially iron supplementation
Assess for pathological causes:
- Evaluate for new onset of iron deficiency, hemolysis, or inflammatory conditions
- Consider changes in underlying disease status in patients with hematologic disorders
Repeat testing:
- If no clear explanation is found, obtain a new properly labeled sample
- Compare results with previous values to confirm findings
Conclusion
MCV delta failures serve as important quality control indicators in laboratory medicine. While they often signal preanalytical errors like sample mislabeling, legitimate physiological changes due to transfusions, transplantation, or disease processes must also be considered. Implementing robust delta check systems that include multiple parameters can significantly improve patient safety by identifying potential errors before clinical decisions are made based on incorrect results.