Ease Into Prep with a USMLE^® Step 2 CK Question of the Day

The correct answer is D. This patient presents with shortness of breath and fever. Physical examination is significant for bilateral crackles, and he has decreased oxygen saturation. The chest x-ray film indicates bilateral lower lung field infiltrates. These nonspecific findings are suggestive of severe pneumonia.

The low lymphocyte count (2% of 4,500 = 90 lymphocytes/mm³, thus the CD4 count must be even lower), however, is suggestive of immunocompromised status. HIV and Pneumocystis jiroveci (formerly carinii) pneumonia (PCP) are very likely possibilities in this patient. Immunofluorescence of an induced sputum sample is required for the definitive diagnosis of PCP. If the test is negative in a patient for whom there is high clinical suspicion of PCP, bronchoscopy with bronchoalveolar lavage (choice B) is warranted. The frequency of PCP infection has decreased with increased awareness of HIV, but it still may be the presenting sign of AIDS.

Arterial blood gases (choice A) would almost certainly demonstrate hypoxia. However, this would not aid in the diagnosis of Pneumocystis pneumonia.

CT scan of the chest (choice C) may be necessary, as it is helpful in determining the extent of the disease. It will suggest the diagnosis of PCP, especially if ground glass opacities are seen, but it is not the definitive diagnostic study.

Liver function tests (choice E) have no role in the diagnosis of PCP.