**Question:** Laboratory diagnosis of thalassemia major are all except:

A. Hemoglobin electrophoresis
B. Complete blood count (CBC)
C. Coombs' test
D. Serum ferritin level

**Core Concept:**
Thalassemia is a group of inherited blood disorders characterized by abnormal production of hemoglobin, leading to reduced red blood cell (RBC) survival and anemia. Thalassemia major is a severe form of thalassemia, requiring regular blood transfusions and chelation therapy to manage symptoms and complications.

**Why the Correct Answer is Right:**
The correct answer is **C. Coombs' test**, as it is not a direct diagnostic tool for thalassemia major. Coombs' test, also known as the direct antiglobulin test (DAT), is used to detect the presence of antibodies and/or immune complexes on the surface of red blood cells (RBCs). It plays a crucial role in evaluating hemolytic anemia, but it is not specific for thalassemia major diagnosis.

**Why Each Wrong Option is Incorrect:**
A. **Hemoglobin electrophoresis (Hb electrophoresis)** is a crucial test for diagnosing thalassemia major as it helps in identifying the abnormal hemoglobin chains produced due to genetic mutations. Thalassemia major is characterized by the presence of α-thalassemia trait or severe α-thalassemia, which leads to the synthesis of abnormal hemoglobin HbH.

B. **Complete blood count (CBC)** provides information about the number and size of RBCs, platelet count, and hemoglobin concentration. Although CBC is essential in diagnosing anemia, it is not specific for thalassemia major diagnosis as it can be affected by various causes of anemia.

D. **Serum ferritin level**: Ferritin is a protein that stores iron in the body. Elevated serum ferritin levels are commonly seen in thalassemia patients due to increased iron absorption and storage. However, serum ferritin level alone is not sufficient for the diagnosis of thalassemia major as it can be elevated in other conditions like chronic liver disease, chronic inflammation, and certain types of cancer.

**Clinical Pearl:**

Thalassemia major is diagnosed by a combination of clinical findings, CBC, serum ferritin levels, and hemoglobin electrophoresis. A characteristic feature of thalassemia major is the presence of Hb H disease (a combination of α-thalassemia trait and severe α-thalassemia), which results in reduced synthesis of α-globin chains.

Core Concept: Hemoglobin electrophoresis is crucial for diagnosing thalassemia major, as it identifies the abnormal hemoglobin HbH disease, which is a hallmark of severe α-thalassemia.

**Why the Correct Answer is Coombs' test:**
Coombs' test helps in diagnosing hemolysis, which is a common complication in thalassemia major patients due to autoantibody formation against RBCs