Although no such algorithm has been formally defined for PCP, clinical differences do exist between HIV-infected patients with PCP compared with other pneumonias; PCP patients have a more subacute onset of disease, ground glass infiltrates on CXR [104], lower oxygen saturation, lower CD4 cell counts, greater weight loss, more cyanosis, more severe dyspnea, and higher respiratory rates than non-PCP patients [15], [105]. Here, CD4 is linked to pneumonia.