What is the next step in managing a patient with a low MCHC and elevated RDW?

Management of Low MCHC and Elevated RDW

The next step in managing a patient with low MCHC (30.3) and elevated RDW (14.5) is to order iron studies including serum ferritin, serum iron, TIBC, and transferrin saturation, as this laboratory pattern strongly suggests iron deficiency anemia. 1

Understanding the Laboratory Values

The presented laboratory values provide important diagnostic clues:

• MCHC 30.3 (low) - indicates decreased hemoglobin concentration in red cells
• RDW 14.5 (elevated) - indicates increased variation in red cell size
• Hematocrit 46.5 (normal) - suggests absence of severe anemia
• Basophils 1.9/0.09% (normal) - not contributory to the current diagnostic question

Diagnostic Significance

The combination of low MCHC and elevated RDW (>14.0%) is particularly significant:

• This pattern is highly suggestive of iron deficiency anemia 2
• An RDW of >14.0% with low MCHC differentiates iron deficiency from thalassemia trait 2, 1
• RDW has been shown to be one of the most sensitive markers for detecting early iron, B12, and folate deficiencies with a sensitivity of 72% for iron deficiency 3

Diagnostic Algorithm

1. Order iron studies:

   • Serum ferritin (most powerful test for iron deficiency)
   • Serum iron
   • Total iron binding capacity (TIBC)
   • Transferrin saturation 2, 1

2. Interpret iron studies:

   • Serum ferritin <12-15 μg/dl is diagnostic of iron deficiency
   • Ferritin between 15-100 μg/dl with transferrin saturation <20% suggests iron deficiency with concurrent inflammation 2, 1
   • Transferrin saturation <30% supports diagnosis of iron deficiency 2

3. If iron studies confirm iron deficiency:

   • Begin oral iron supplementation with 35-65 mg elemental iron daily
   • Options include ferrous sulfate 200 mg twice daily, ferrous fumarate, or ferrous gluconate 1
   • Continue treatment for 3 months after hemoglobin normalizes to replenish iron stores 1

4. If iron studies are normal or equivocal:

   • Consider hemoglobin electrophoresis to rule out thalassemia trait 1
   • Check vitamin B12 and folate levels as deficiencies can coexist 1, 3

Additional Investigations

If iron deficiency is confirmed, the underlying cause must be identified:

• Gastrointestinal evaluation is essential unless there is a clear non-GI source of blood loss 2
  • Upper GI endoscopy with small bowel biopsies (to rule out celiac disease)
  • Colonoscopy (especially important in older patients)

Monitoring and Follow-up

• Expect hemoglobin improvement of 1-2 g/dL within 2-4 weeks of starting iron therapy 1
• Check hemoglobin weekly until stable, then monthly 1
• Monitor iron parameters (ferritin, transferrin saturation) regularly 1

Common Pitfalls to Avoid

1. Accepting dietary deficiency as the sole cause without investigating potential GI sources of blood loss 1
2. Inadequate duration of iron therapy (should continue for 3 months after normalization) 1
3. Misinterpreting ferritin levels in the presence of inflammation (ferritin is an acute phase reactant) 1
4. Failing to evaluate for other nutrient deficiencies in persistent anemia 1
5. Deferring iron replacement while awaiting investigations 1

The combination of low MCHC and elevated RDW has been shown to have good diagnostic accuracy for iron deficiency with an area under the ROC curve of 0.71 for MCHC and 0.73 for RDW in recent studies 4, 5, making these reliable parameters to guide initial management decisions.