Sera from patients with active pulmonary tuberculosis and pulmonary diseases frequently mimicking tuberculosis were assayed for immunoglobulin G antibody activity to purified protein derivative (PPD) by an enzyme-linked immunosorbent assay. A method of standardization was developed to limit assay variation. Patients with active pulmonary tuberculosis had a significantly greater mean level of antibody than had patients with atypical tuberculosis (P = 0.005), sarcoidosis (P = 0.0001), histoplasmosis (P = 0.004), blastomycosis (P = 0.008), or cryptococcosis (P = 0.017), patients who had received bacille Calmette-Guérin vaccination (P = 0.003) or who had a history of treated tuberculosis (P = 0.003), and PPD skin test-positive and skin test-negative control subjects (P = 0.001). This technique may have potential use as a rapid diagnostic aid in evaluating patients with suspected active pulmonary tuberculosis.

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Three patients with culture-proven Mycobacterium tuberculosis meningitis were studied. Analysis of cerebrospinal fluid with an enzyme-linked immunosorbent assay (ELISA) method measuring IgG antibody to purified protein derivative rapidly yielded positive results, whereas results of acid-fast smears were negative and cultures took several weeks before growth appeared. We did serial studies of cerebrospinal fluid and sera from one patient. Initially, greater amounts of IgG antibody to purified protein derivative were present in the cerebrospinal fluid than in the serum. The antibody level in the cerebrospinal fluid paralleled the patient's clinical course, cerebrospinal fluid cell count, protein level, and glucose level. Cerebrospinal fluid samples from 33 hospitalized control patients were negative for antibody to purified protein derivative. The ELISA method measuring IgG antibody to purified protein derivative should be evaluated as a means of early diagnosis and management of patients with suspected tuberculous meningitis.