How to interpret normal automated hematology results (White Blood Cell count 8.24, Red Blood Cell count 4.73, Hemoglobin 12.2, Hematocrit 38.6%, Mean Corpuscular Volume (MCV) 81.6, Mean Corpuscular Hemoglobin (MCH) 25.8, Mean Corpuscular Hemoglobin Concentration (MCHC) 31.6, Red Cell Distribution Width (RDW) 16.1%, Platelet count 279) in a 30-year-old female with potential restless legs syndrome?

Interpretation of CBC Results in a 30-Year-Old Female

This patient has mild microcytic hypochromic anemia with elevated RDW, which strongly suggests iron deficiency anemia and requires immediate iron studies (serum ferritin and transferrin saturation) to confirm the diagnosis and guide treatment. 1, 2

Key Abnormal Findings

The critical abnormalities in this CBC are:

• Hemoglobin 12.2 g/dL: Mild anemia (WHO defines anemia as Hb <12 g/dL in non-pregnant women) 2
• MCV 81.6 fL: Low-normal to borderline microcytic (normal range typically 80-100 fL) 2
• MCH 25.8 pg: Low, indicating hypochromic red cells (this is a more reliable marker of iron deficiency than MCHC) 2
• MCHC 31.6 g/dL: Low, reflecting hypochromia from iron-restricted erythropoiesis 1
• RDW 16.1%: Elevated (normal <14-15%), indicating increased variation in red cell size 2

Clinical Significance

The combination of low MCH with elevated RDW is highly suggestive of iron deficiency, even when other CBC parameters remain relatively normal, with a sensitivity of 72% for detecting iron deficiency in patients with anemia. 2 This pattern indicates that the bone marrow is producing red blood cells with progressively less hemoglobin content, while both normal-sized older cells and smaller, hypochromic newer cells coexist in circulation, creating the high RDW. 2

The low MCHC specifically reflects hypochromic cells resulting from severe iron restriction during red blood cell production. 1 This is particularly important because low MCHC is the most important indicator requiring comprehensive evaluation to exclude serious underlying causes, including gastrointestinal malignancy in appropriate populations. 1

Immediate Diagnostic Workup Required

Essential Iron Studies

You must obtain the following tests immediately:

• Serum ferritin: <30 μg/L confirms iron deficiency without inflammation; <12 μg/L is diagnostic per WHO criteria 3, 1, 2
• Transferrin saturation (TSAT): <16-20% supports iron deficiency and is less affected by inflammation than ferritin 3, 1, 2
• C-reactive protein: To assess for inflammation, which can falsely elevate ferritin 3, 2
• Reticulocyte count: To evaluate bone marrow response to anemia 3, 2

Interpretation of Iron Studies

• If ferritin <30 μg/L without inflammation: Confirms iron deficiency 3, 2
• If ferritin 30-100 μg/L with inflammation: Still consistent with iron deficiency 3
• If ferritin >100 μg/L with TSAT <20%: Suggests anemia of chronic disease 3
• If ferritin 30-100 μg/L: Likely combination of iron deficiency and anemia of chronic disease 3

Investigation for Underlying Cause

In Premenopausal Women (This Patient)

The most common cause is menstrual blood loss. 1 However, you must still assess for:

• Dietary iron intake adequacy 1
• Gastrointestinal symptoms (even mild) 1
• History of blood donation 1

Critical Pitfall to Avoid

Do not attribute low MCHC to dietary insufficiency or menstruation without excluding gastrointestinal malignancy if the patient has any concerning features (family history, GI symptoms, failure to respond to iron therapy). 1 While this patient is young and premenopausal (making menstrual loss most likely), all adult men and post-menopausal women with iron deficiency require both upper endoscopy and colonoscopy to exclude malignancy, even without overt blood loss. 1

Connection to Restless Legs Syndrome

Given the context of potential RLS mentioned in the expanded question:

Iron deficiency is a well-established secondary cause of restless legs syndrome, and ferritin levels should be checked at presentation and with worsened RLS symptoms. 4, 5 Iron-replacement therapy is a first-line management option for RLS patients with evidence of reduced body-iron stores. 4 Correction of iron deficiency improves RLS symptoms in patients with low ferritin levels. 6

Treatment Approach

Once iron deficiency is confirmed:

• Oral iron supplementation is first-line for premenopausal women with iron deficiency 3, 2
• Intravenous iron may be considered if oral iron is not tolerated or absorbed, or when rapid repletion is needed 2
• Treatment of the underlying cause cures the anemia 1
• Monitor response with repeat CBC and iron studies after 1-3 months of therapy 3

Additional Differential Considerations

If iron studies are normal, consider:

• Thalassemia trait: Distinguished by normal or low RDW (<14%), elevated red cell count, and requires hemoglobin electrophoresis for confirmation 1
• Chronic inflammatory conditions: Less commonly cause low MCHC than iron deficiency; CRP helps identify inflammatory contribution 1
• Combined nutritional deficiencies: Iron plus folate or B12 deficiency may mask microcytosis but show elevated RDW 1