Enzyme-linked immunosorbent assay (ELISA) of antibodies to purified protein derivative (PPD) in the diagnosis of active tuberculosis: evaluation of its potential and limitation in a high prevalence area.

Sera from patients with active tuberculosis were assayed for IgG antibodies to purified protein derivative (PPD) by an enzyme-linked immunosorbent assay (ELISA) technique. Eighty seven of the 112 patients (78%) with sputum culture-positive, and 57 of 78 patients (73%) with sputum culture-negative, pulmonary tuberculosis had positive serology. Seventeen of 19 patients (89%) with renal tuberculosis (demonstrable lesion on intravenous pyelography) had antibody to PPD, whereas only 3 of 9 patients (33%) with urinary tuberculosis (positive urine culture only, without abnormality on intravenous pyelography) and 8 of 21 patients (38%) with tuberculous cervical lymphadenitis had positive serology. Seropositivity rate in paediatric patients was also low, only 2 out of 8 patients gave positive serology. Thus, the diagnostic value of this test is limited as a positive result is obtained only when the disease is relatively long-standing or extensive.