Study objectives: To determine whether an algorithm consisting of a chest radiograph and the diffusing capacity of the lung for carbon monoxide (D(LCO)) is effective in detecting Pneumocystis carinii pneumonia (PCP) in symptomatic HIV-infected persons; and to establish a benchmark for future comparisons of alternative algorithms.
Design: Prospective, 64-month study.
Setting: Multicenter, ambulatory care.
Patients: 306 HIV-infected subjects enrolled in the Pulmonary Complications of HIV Infection Study who developed 467 episodes of new or worsening respiratory symptoms.
Measurements: Chest radiography followed by D(LCO) measurement, if the radiograph was normal or unchanged.
Results: An algorithm combining a chest radiograph followed by a D(LCO) measurement, if the radiograph was normal or unchanged, was effective and detected abnormalities that led to a diagnosis of PCP in 78 of 80 evaluable episodes (97.5%). The radiograph (specific parenchymal abnormality, number of lung zones involved) and the D(LCO) (degree of decrease, degree of decrease from baseline) also provided additional information on the probability of PCP.
Conclusions: In symptomatic HIV-infected patients suspected of having PCP, the diagnostic evaluation should begin with a chest radiograph, followed by a D(LCO) measurement, if the radiograph is normal or unchanged. If both of these tests are normal, it may be reasonable to conclude the evaluation rather than to proceed on to additional testing. This algorithm can serve as a benchmark for future comparisons.