High MCHC: Significance and Management
A high MCHC is almost always a laboratory artifact requiring immediate investigation for pre-analytical errors, with true elevations being physiologically rare and pointing to specific hemolytic conditions like hereditary spherocytosis or hemoglobin SC disease.
Understanding the Significance
High MCHC values above the reference range (typically >365 g/L) are not physiologically possible under normal circumstances due to hemoglobin solubility limitations 1. When you encounter an elevated MCHC, you're dealing with one of two scenarios:
1. Laboratory Artifacts (Most Common)
The majority of high MCHC results are spurious and caused by:
- Cold agglutination: RBC clumping at room temperature that resolves with 37°C water bath warming 2
- Lipemia: Optical interference from lipid-rich plasma requiring plasma exchange 2
- RBC agglutination: Can be corrected using optical parameters (RBC-O, HGB-O) from flow cytometry 3
Critical action: Before pursuing clinical workup, verify the result by examining the blood smear and checking for interfering factors 3, 2. The newer Sysmex XN-10 optical parameters can efficiently correct 92% (36/39) of spurious elevations from agglutination or optical interference 3.
2. True Pathological Elevations (Rare)
When artifacts are excluded, high MCHC indicates:
- Hereditary spherocytosis: The classic cause of true MCHC elevation
- Hemoglobin SC disease: These patients have abnormally elevated intracellular hemoglobin concentration 4
- Other hemolytic anemias: Requiring systematic peripheral smear examination 1
Evaluation Algorithm
Step 1: Verify the Result
- Examine the peripheral blood smear immediately - this is non-negotiable 1
- Check for spherocytes, agglutination, or other RBC abnormalities
- Review the sample for lipemia or hemolysis
Step 2: Rule Out Artifacts
- If cold agglutination suspected: Warm sample to 37°C and retest 2
- If lipemia present: Perform plasma exchange and retest 2
- If available: Use optical flow cytometry parameters (RBC-O, HGB-O) to bypass impedance-based errors 3
Step 3: If True Elevation Confirmed
- Obtain complete blood count with attention to all cell lines 5
- Calculate reticulocyte count to assess bone marrow response 5
- Perform osmotic fragility testing if spherocytosis suspected
- Consider hemoglobin electrophoresis for hemoglobinopathies 4
- Evaluate for hemolysis markers: LDH, indirect bilirubin, haptoglobin
Step 4: Assess for Hemolytic Anemia
Use reticulocyte parameters to create an RBC disease score - this achieves 94% sensitivity (17/18) for detecting true RBC pathology 3. Look for:
- Evidence of increased RBC destruction
- Abnormalities in multiple cell lines warranting hematology consultation 5
Common Pitfalls to Avoid
Don't pursue extensive workup without first confirming the result - most high MCHC values are artifacts 3, 2
Don't rely solely on automated parameters - the peripheral smear is essential for definitive diagnosis 1
Don't ignore the clinical context - in hemoglobin SC disease, the elevated MCHC contributes to pathophysiology including decreased oxygen affinity, increased viscosity, and accelerated sickling 4
Don't confuse with low MCHC - while low MCHC suggests iron deficiency or thalassemia, high MCHC has completely different differential diagnoses
Clinical Implications
For confirmed pathological elevations, the high MCHC has direct consequences on morbidity:
- Increased blood viscosity when deoxygenated 4
- Enhanced sickling rates in SC disease 4
- Accelerated hemolysis in spherocytosis
The key is rapid differentiation between artifact and true pathology through systematic evaluation, with the peripheral smear serving as your definitive diagnostic tool.