Deoxyribonucleic acid output in the sputum from cystic fibrosis patients

The deoxyribonucleic acid (DNA) content of sputum from cystic fibrosis patients was examined to establish if it was likely to be a useful indicator of worsening clinical condition. The assay was reproducible (coefficient of variation 4.2%) and added DNA could be demonstrated. Added antibiotics did not influence the result. The daily DNA content in the sputum showed similar variations to the weight, but the DNA output (content X weight/24 h) was perhaps a more sensitive indicator of clinical status. There was a weak, negative correlation between DNA output and peak expiratory flow rate.