The acceptable range for hemoglobin values on a control sample is 13 ± 0.4 g/dL. A hemoglobin determination is performed five times in succession on the same control sample. The results are (in g/dL: 12, 12.3, 12, 12.2, and 12.1). These results are:

Correct Answer: A

Rationale: Rationale for Choice A: The results are precise but not accurate. Precision refers to the consistency of results, which is evident as the values are close to each other (12, 12.3, 12, 12.2, and 12.1). However, accuracy refers to how close the results are to the true value. Since the average of the results is outside the acceptable range (12.12 g/dL vs. 13 g/dL), they are not accurate. Therefore, the correct choice is A. Summary of other choices: B: Both accurate and precise - Inaccurate as the average value is outside the acceptable range. C: Accurate, but not precise - Inaccurate as the results are not consistent. D: Neither accurate nor precise - Results are precise (consistent) but not accurate.

Correct Answer: B

Rationale: The most likely diagnosis for this man is Acute Myeloid Leukemia (AML) based on his symptoms of breathlessness, bone pain, severe infections, hepatosplenomegaly, and gum hypertrophy. AML is characterized by rapid growth of abnormal white blood cells in the bone marrow, leading to bone pain, infections, and organomegaly. The presence of gum hypertrophy is a classic finding in AML due to infiltration of leukemic cells. In contrast, Multiple Myeloma (choice A) presents with bone pain, anemia, and kidney issues; Chronic Lymphocytic Leukemia (choice C) typically manifests with lymphadenopathy and anemia; and Hodgkin Lymphoma (choice D) presents with painless lymphadenopathy, fever, night sweats, and weight loss. Therefore, AML is the most fitting diagnosis in this case.

Correct Answer: D

Rationale: The correct answer is D: an IgG-IgM response to penicillin. 1. The symptoms of fever, rash, and proteinuria are suggestive of a hypersensitivity reaction to penicillin. 2. The timing of 7 days after penicillin initiation is consistent with a delayed hypersensitivity reaction mediated by IgG and IgM antibodies. 3. Recurrence of rheumatic fever typically occurs weeks to months after the initial episode, making choice A incorrect. 4. Choice B is unlikely given the temporal relationship with penicillin therapy. 5. Choice C is incorrect as an IgE response would present as an immediate hypersensitivity reaction, not after 7 days.

Correct Answer: C

Rationale: The correct answer is C because T lymphocytes play a crucial role in the rejection of polyomavirus-induced tumors. This is evident from the fact that nude mice, which lack functional T lymphocytes, develop tumors when infected with polyomavirus, whereas normal mice with intact T lymphocytes do not. Choice A is incorrect because macrophages are not the main players in rejecting these tumors. Choice B is incorrect as natural killer cells alone cannot reject these tumors without the help of T lymphocytes. Choice D is incorrect as B lymphocytes may also contribute to the rejection process, although they are not the primary effector cells in this context.

Correct Answer: B

Rationale: The correct answer is B because a positive tuberculin skin test indicates a cell-mediated immune response. This is because the test measures the response of T cells to the antigen, which is indicative of an active cellular immune response against Mycobacterium tuberculosis. Option A is incorrect as it refers to a humoral immune response involving antibodies produced by B cells. Option C is incorrect because the test specifically assesses T cell function, not both T and B cells. Option D is incorrect as it implies that only B cells are responsible for the positive skin test, which is not the case.