Aplastic anemia is a disorder in which the bone marrow cells that develop into mature blood cells become damaged. The damaged bone marrow cells can lead to low numbers of red blood cells, white blood cells, and/or platelets. When the cause of aplastic anemia cannot be diagnosed, the cause is likely which of the following?

Correct Answer: A

Rationale: Rationale for Choice A (Correct Answer - An autoimmune disorder): 1. Aplastic anemia is often associated with autoimmune disorders where the immune system attacks the bone marrow cells. 2. In aplastic anemia of unknown cause, autoimmune reactions are a common underlying mechanism. 3. Autoimmune disorders can disrupt the bone marrow's ability to produce healthy blood cells. Summary of Other Choices: B: Chemotherapy drugs - While chemotherapy can cause aplastic anemia, the question specifies an unknown cause. C: Radiation exposure - Radiation exposure can lead to aplastic anemia, but the question specifies an unknown cause. D: Toxins - Toxins can contribute to aplastic anemia, but the question implies an undiagnosed origin.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Hydroxyurea inhibits the enzyme xanthine oxidase, reducing the conversion of xanthine to uric acid. 2. This leads to decreased production of uric acid, resulting in lower serum uric acid levels. 3. Therefore, the statement that hydroxyurea increases serum uric acid levels is FALSE. 4. Choices B, C, and D are incorrect as they do not align with the pharmacological mechanism of hydroxyurea in reducing uric acid levels.

Correct Answer: D

Rationale: The correct answer is D: Pulmonary embolism. A pulmonary embolism occurs when a blood clot from another part of the body, typically the legs (DVT), travels to the lungs and blocks a pulmonary artery. This can be fatal if not promptly treated. Thromboembolism (A) is a general term for blood clots that travel in the bloodstream. DVT (B) specifically refers to a blood clot in a deep vein, often in the legs. PAD (C) stands for peripheral artery disease, which is caused by atherosclerosis and results in reduced blood flow to the extremities, but it does not typically lead to fatal clot formation in the circulation like a pulmonary embolism does.

Correct Answer: A

Rationale: The correct answer is A: TRUE. PCR amplifies DNA, making it sensitive enough to detect low numbers of neoplastic cells, even in patients with reduced cell counts due to treatment. This can help in early detection of relapse. Choice B is incorrect because PCR can indeed improve sensitivity in such cases. Choice C is incorrect as PCR consistently enhances sensitivity. Choice D is incorrect as PCR can be used in both remission and relapse scenarios.

Correct Answer: A

Rationale: Step 1: Intravascular hemolysis occurs within blood vessels due to mechanical trauma. Step 2: Trauma to red blood cells (RBCs) while in circulation can lead to their destruction. Step 3: This destruction releases hemoglobin into the bloodstream. Step 4: The released hemoglobin can cause complications like kidney damage. Step 5: Therefore, intravascular hemolysis is the result of trauma to RBCs in circulation. Summary: Choice A is correct because trauma to RBCs in circulation can indeed lead to intravascular hemolysis. Choices B, C, and D are incorrect because they do not accurately reflect the process of intravascular hemolysis.