Final answer:
The classical marker elevated in pulmonary fluid of a patient with Pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii is β-D-glucan. Diagnosis is confirmed by direct immunofluorescence assay or PCR, and treatment typically involves trimethoprim-sulfamethoxazole.
Step-by-step explanation:
The question is asking about a clinically elevated marker that would be found in the pulmonary fluid of a patient with CXR showing diffuse B/L ground glass infiltrates and who has Pneumocystis jirovecii infection. This is a classical presentation of Pneumocystis pneumonia (PCP), which is particularly common in immunocompromised patients, such as those taking high dose immunosuppressants or those with HIV/AIDS. In PCP, the elevated marker commonly seen is β-D-glucan from the pulmonary fluid. Diagnosis is often made by a direct immunofluorescence assay (DFA) or PCR test. The treatment typically involves the combination drug trimethoprim-sulfamethoxazole (TMP/SMZ). It is crucial to diagnose and treat PCP promptly, as it can be fatal if left untreated, especially in patients with compromised immune systems.