What does an elevated hematocrit and low MCHC indicate in a blood test?

Interpretation of Elevated Hematocrit and Low MCHC in Blood Test Results

The combination of elevated hematocrit (47.8%) and low MCHC (29.7%) most likely indicates mild dehydration with possible early iron deficiency, which should be confirmed with additional testing including serum ferritin and iron studies.

Understanding the Abnormal Values

• The hematocrit of 47.8% is above the high normal range, indicating a relative increase in the proportion of red blood cells in the blood volume 1
• The MCHC (Mean Corpuscular Hemoglobin Concentration) of 29.7% is below the low normal range, suggesting decreased hemoglobin concentration within red blood cells 1
• Other values including hemoglobin (14.2), MCV (96), and RBC count (4.99) are within normal ranges 1

Potential Causes

Relative Polycythemia (Elevated Hematocrit)

• Dehydration is the most common cause of relative polycythemia, resulting from plasma volume depletion while red cell mass remains constant 1
• Common causes include inadequate fluid intake, excessive fluid loss (diarrhea, vomiting, diuretics use), or conditions causing capillary leak 1
• Stress polycythemia (Gaisböck syndrome) is associated with hypertension and emotional stress, though this concept has limited foundation 1
• Smoker's polycythemia from chronic carbon monoxide exposure should be considered in smokers 1

Low MCHC

• Low MCHC typically indicates hypochromia, most commonly seen in iron deficiency 1
• The combination with normal MCV (96) suggests early iron deficiency before microcytosis develops 1
• Technical factors may affect MCHC measurement, as electronic cell counters can underestimate MCHC in certain conditions 2, 3

Diagnostic Algorithm

1. Assess for dehydration

   • Review clinical signs of dehydration (skin turgor, mucous membrane dryness, orthostatic changes) 1
   • Obtain history of fluid intake, losses, and medication use 1

2. Evaluate for true vs. relative polycythemia

   • If dehydration is suspected, recheck CBC after adequate hydration 1
   • Consider serum erythropoietin (EPO) level if true polycythemia is suspected 1

3. Investigate iron status

   • Order serum ferritin, iron, total iron binding capacity, and transferrin saturation 1
   • These biochemical tests detect earlier changes in iron status than hematological parameters 1

4. Rule out other causes

   • Consider hemoglobinopathies if iron studies are normal 4
   • Evaluate for chronic hypoxic conditions if elevated hematocrit persists after hydration 1

Clinical Significance and Management

• Mild elevation of hematocrit with low MCHC is unlikely to cause significant clinical symptoms 1

• If dehydration is confirmed:

  • Increase oral fluid intake or provide IV fluids if necessary 1
  • Address underlying causes of fluid loss 1

• If iron deficiency is confirmed:

  • Initiate oral iron supplementation 1
  • Investigate potential causes of iron deficiency (blood loss, malabsorption, poor intake) 1

Common Pitfalls to Avoid

• Do not assume that elevated hematocrit always indicates true polycythemia; relative polycythemia from dehydration is more common 1
• Avoid attributing low MCHC solely to laboratory error without investigating iron status 2, 3
• Remember that normal hemoglobin does not rule out early iron deficiency 1
• Be aware that electronic cell counters may produce inaccurate MCHC values, especially in dehydrated cells 2

Follow-up Recommendations

• Repeat CBC after ensuring adequate hydration 1
• If hematocrit normalizes but MCHC remains low, proceed with iron studies 1
• If hematocrit remains elevated despite adequate hydration, consider evaluation for true polycythemia 1