PUlmonary alveolar proteinosis: shunt fraction and lactic acid dehydrogenase concentration as aids to diagnosis.

The shunt fraction breathing 100 per cent O2 and serum lactic acid dehydrogenase concentration were evaluated as 2 easily obtainable, rapid laboratory procedures that might aid in the early diagnosis of pulmonary alveolar proteinosis. The mean +/- SE shunt fraction was 20 +/- 1.2 per cent in patients with alveolar proteinosis compared to 8.9 +/- 0.5 per cent in other groups of patients with diffuse lung disease (P less than 0.001). The lactic acid dehydrogenase concentration was increased in all patients with alveolar proteinosis and helped to separate further the 2 groups. Thus, when a patient presents with the findings of chronic diffuse lung disease, the lactic acid dehydrogenase concentration and the shunt fraction can be of value in suggesting the diagnosis of pulmonary alveolar proteinosis.