Macrocytosis in CBC can be diagnosed by –
**Core Concept**
Macrocytosis refers to the presence of macrocytes (large cells) in the peripheral blood smear, which is a characteristic feature of megaloblastic anemia. This condition is caused by impaired DNA synthesis due to a deficiency in either vitamin B12 or folate. The resulting megaloblastic changes affect the production of red blood cells, leading to macrocytosis.
**Why the Correct Answer is Right**
The correct answer is related to the diagnostic criteria for macrocytosis, which involves the measurement of red blood cell (RBC) indices on a complete blood count (CBC). Macrocytosis is typically defined as a mean corpuscular volume (MCV) of 100 μm^3 or higher. This is because megaloblastic anemia leads to an increase in the size of RBCs, resulting in an elevated MCV. The MCV is a critical parameter in differentiating macrocytosis from other forms of anemia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while a low hemoglobin level may be associated with anemia, it is not a specific indicator of macrocytosis. Anemia can be caused by various factors, including iron deficiency, chronic disease, or blood loss.
**Option B:** This option is incorrect because a low platelet count (thrombocytopenia) is not a characteristic feature of macrocytosis. Thrombocytopenia is typically associated with bone marrow failure or suppression.
**Option C:** This option is incorrect because a high white blood cell count (leukocytosis) is not a specific indicator of macrocytosis. Leukocytosis can be caused by various factors, including infection, inflammation, or stress.
**Clinical Pearl / High-Yield Fact**
When interpreting a CBC, remember that macrocytosis is often associated with megaloblastic anemia, which can be caused by a deficiency in either vitamin B12 or folate. This is why patients with macrocytosis may also present with neurological symptoms, such as weakness or numbness in the extremities.
**Correct Answer:** C. Elevated mean corpuscular volume (MCV) on a complete blood count (CBC).