**Question:** First investigation to be done in a patient with thrombocytopenia: September 2008

**Core Concept:** Thrombocytopenia is a medical condition characterized by a decrease in the number of platelets in the blood, which can lead to bleeding complications. The appropriate initial investigation depends on the suspected cause of thrombocytopenia.

**Why the Correct Answer is Right:**

Correct Answer: C. Complete blood count (CBC)

In patients with suspected thrombocytopenia, a complete blood count (CBC) should be performed first to assess the overall health status, check for any concurrent infections or inflammation (indicated by elevated white blood cell count), and identify any specific causes of thrombocytopenia. A normal CBC result does not exclude thrombocytopenia, but it narrows down the potential causes.

**Why Each Wrong Option is Incorrect:**

A. Platelet count (PT) and partial thromboplastin time (PTT) are important tests in evaluating thrombocytopenia, but they are not the initial investigation. CBC should be performed first to assess the overall health status and identify any underlying causes.

B. Peripheral blood smear is useful for identifying morphological abnormalities of platelets and red blood cells, but it is not the first investigation to be done in thrombocytopenia. CBC and platelet count should be performed first.

D. Bone marrow aspiration and biopsy are more invasive procedures used to evaluate the bone marrow for abnormalities that may lead to thrombocytopenia. These procedures should be considered after a normal CBC and platelet count are obtained to further investigate the cause of thrombocytopenia.

**Clinical Pearl:**

Thrombocytopenia can be caused by various factors, including infections, autoimmune disorders, medications, or malignancies. A thorough clinical history, physical examination, and initial laboratory tests like CBC help narrow down the potential causes. Further investigations, like bone marrow aspiration and biopsy or specific tests for infections or autoimmune disorders, will be needed based on the initial results and clinical context. A comprehensive evaluation is crucial to identify the underlying cause and guide appropriate management.

**Correct Answer Explanation:**

C. Complete blood count (CBC) is the first step to assess the patient with thrombocytopenia, as it helps identify the overall health status, detect infections, and rule out any underlying diseases like leukemia or lymphoma.

**Why the Correct Answer is Right:**

Performing a CBC allows for an evaluation of the patient's overall health status, as well as the presence of any infections or inflammation, which may be contributing factors to thrombocytopenia. A normal CBC does not exclude the possibility of thrombocytopenia, but it helps to narrow down the potential causes and guide further diagnostic workup.

**Why Each Wrong Option is Incorrect:**

A. Platelet count (PLT) is important in evaluating thrombocytopenia, but it should be performed after a CBC to confirm the platelet count and identify any abnormalities.

B. Peripheral blood smear is essential for evaluating the morphology of platelets and red blood cells, but it is not the initial investigation