Raised PPD antibodies in active pulmonary tuberculosis.

Antibodies to purified protein derivative of tuberculin (PPD) were measured in 47 patients with active pulmonary tuberculosis and in various control subjects using an enzyme linked immunosorbent assay. Raised IgG anti PPD antibodies were found in 30 patients with active tuberculosis, in one of 28 patients with miscellaneous non tuberculous diseases and in one of 49 healthy control subjects. This gave the assay a sensitivity of 65% and a specificity of 98%. Antibodies were also measured in a further 20 patients with suspected tuberculosis but in whom microbiological evidence was absent. In eight of these patients active tuberculous disease was subsequently validated on the basis of clinical response to chemotherapy: raised PPD antibodies were found in six of this group but in none of the remaining 12 patients in whom the diagnosis of tuberculosis was considered doubtful. Further studies showed that patients' PPD antibody level fell over a one year period of successful therapy and that tuberculin skin testing and BCG vaccination did not cause a rise in antibodies in healthy subjects. These results suggest that the measurement of PPD antibodies is a useful adjunctive test in the diagnosis of tuberculosis.