text: LDH is often measured in HIV patients as a non-specific marker for pneumonia due to Pneumocystis jirovecii (PCP). Elevated LDH in the setting of upper respiratory symptoms in a HIV patient suggests, but is not diagnostic for, PCP. However, in HIV-positive patients with respiratory symptoms, a very high LDH level (>600 IU/L) indicated histoplasmosis (9.33 times more likely) in a study of 120 PCP and 30 histoplasmosis patients.