A patient presents with microcytic anemia, an elevated RBC count, and a Mentzer index of less than 13. What is the next appropriate investigation?

1. A

   S. Ferritin

2. B

   Bone marrow biopsy

3. C

   S. Transferrin

4. D

   Hb electrophoresis

Appeared in: INI-CET EXAM -2025

Explanation

• The combination of microcytic anemia (low MCV) with a disproportionately high RBC count is a classic finding in Thalassemia trait.
• The Mentzer Index (MCV/RBC count) is a calculated value used to differentiate between Iron Deficiency Anemia (IDA) and Thalassemia trait. A value less than 13, as seen in this patient, strongly suggests Thalassemia.
• Hb electrophoresis is the definitive diagnostic test for hemoglobinopathies. It separates and quantifies different hemoglobin types, revealing characteristic patterns for conditions like beta-thalassemia (e.g., elevated HbA2).

Why Other Options Were Wrong

• Option A: Serum ferritin measures the body's iron stores. While it is the key test for diagnosing iron deficiency anemia, the patient's other findings (high RBC count, Mentzer index < 13) make iron deficiency less likely than thalassemia.
• Option B: A bone marrow biopsy is an invasive and costly procedure. It is not indicated for the initial workup of a suspected, uncomplicated case of thalassemia trait.
• Option C: Serum transferrin, like ferritin, is part of the iron studies panel. It is used to evaluate iron deficiency, where it is typically elevated (as part of Total Iron Binding Capacity - TIBC). It is not the primary test to confirm thalassemia.

Related Visual

• Visual 1: Table: A comparative table showing the typical laboratory findings (MCV, RBC, RDW, Mentzer Index, Ferritin) for Iron Deficiency Anemia versus Thalassemia Trait.
• Visual 2: Diagram: A sample Hb electrophoresis report illustrating the normal percentages of HbA, HbA2, and HbF, contrasted with a report from a patient with beta-thalassemia trait showing an elevated HbA2 peak.

Clinical Relevance

• Nursing practice connection: Use the key finding related to Differential diagnosis of microcytic anemia based on laboratory indices to guide bedside assessment, documentation, and the next nursing action.
• Correctly differentiating thalassemia trait from iron deficiency anemia is crucial to prevent inappropriate and potentially harmful iron supplementation. Patients with thalassemia have normal or high iron stores, and giving them extra iron can lead to iron overload (hemosiderosis).
• Identifying individuals with thalassemia trait is important for genetic counseling, especially for family planning, to assess the risk of having a child with a severe form of thalassemia (thalassemia major).
• What if? If the patient's Mentzer index was 16 and the RBC count was low, the most likely diagnosis would shift to Iron Deficiency Anemia, and the next appropriate investigation would be Serum Ferritin.

How to Approach the Question

• First, identify the key laboratory findings provided in the stem: microcytic anemia, elevated RBC count, and a specific Mentzer index value.
• Recognize that microcytic anemia has two main differential diagnoses: Iron Deficiency Anemia (IDA) and Thalassemia.
• Recall or calculate the Mentzer index (MCV/RBC). Understand that a value less than 13 points towards Thalassemia, while a value greater than 13 points towards IDA.
• Apply this knowledge to the patient's case. The findings are classic for Thalassemia trait.
• Evaluate the options to determine which test is the definitive or confirmatory investigation for the suspected diagnosis.
• Eliminate tests for the less likely diagnosis (S. Ferritin for IDA) and overly invasive procedures (Bone marrow biopsy), selecting the gold standard test for the most likely diagnosis (Hb electrophoresis for Thalassemia).

Concept Tested & Keywords

• Concept Tested: Differential diagnosis of microcytic anemia based on laboratory indices.
• Stem keywords: microcytic anemia, elevated RBC count, Mentzer index
• Lead-in keywords: next appropriate investigation
• Clinical cues: Mentzer index less than 13 is a strong indicator for Thalassemia trait over Iron Deficiency Anemia.

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Q1alSFoTWMSQ1w7ZowpMXe

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