Acceptability of low-volume, induced sputum specimens for diagnosis of Pneumocystis carinii pneumonia

Two milliliters of induced sputum is the minimum volume recommended for microscopic examination for Pneumocystis carinii by direct fluorescent antibody (DFA) stain. Many specimens received in our laboratory do not meet this criterion. Rejection of these inadequate specimens increases cost and discomfort to the patient because additional specimens must be obtained. To determine whether volumes less than 2 mL were acceptable for microscopic analysis, we examined 177 consecutive induced sputum specimens submitted for P carinii DFA stain. Eighty-four (47.4%) specimens were less (0.5-1.9 mL) than the 2-mL volume recommended by the manufacturer. Overall, 33 specimens were positive. The positivity rates for specimens 2 mL or more and less than 2 mL were 18% and 19%, respectively. Induced sputum volumes between 0.5 and 2 mL may be acceptable for DFA examination.