Serum angiotensin converting enzyme in sarcoidosis: sensitivity and specificity in diagnosis: correlations with disease activity, duration, extra-thoracic involvement, radiographic type and therapy.

Serum angiotensin converting enzyme (SACE), despite certain limitations, has been found to be a useful adjunct to the diagnosis, assessment of disease activity, and management of sarcoidosis. The spectrofluorimetric assay was used to measure SACE in 50 normal controls, 76 patients with tuberculosis (42 pulmonary, 16 lymphatic and 18 military cases), 20 patients with cryptogenic fibrosing alveolitis, 50 patients with silicosis, three patients with extrinsic allergic alveolitis, 10 patients with Crohn's disease, two patients with Gaucher's disease, and 128 patients with sarcoidosis on 303 occasions (144 during periods judged as clinically active and 189 inactive). Our results show a normal range (mean +/- 2SD) of 19-54 nmol/ml/min. The false positive rate is 2 per cent in normal controls, 9.2 per cent in tuberculosis (38.9 per cent in military but 0 per cent in the other forms), 48 per cent in silicosis, 100 per cent in Gaucher's disease, and 0 per cent in the other diseases. The sensitivity, specificity, positive and negative predictive values were 58.1, 83.8, 83.8 and 58.1 per cent respectively. The sensitivity rose to 85.9 per cent if only those samples taken from patients in whom sarcoidosis was suspected on initial presentation were included, and 92.1 per cent if only those with clinically active sarcoidosis were included. The sensitivity of SACE as a diagnostic test in sarcoidosis is thus influenced by the relative frequency of active and inactive sarcoidosis. The specificity is influenced by the prevalence of military tuberculosis and silicosis, but is uninfluenced by other common varieties of interstitial lung disease such as cryptogenic fibrosing alveolitis and extrinsic allergic alveolitis, or by other non-pulmonary granulomatous disease. There was no correlation of the SACE level with age, sex, population group, associated other illness or duration of sarcoidosis. Statistically, SACE levels were significantly higher in patients with Types II and III chest radiographs as compared to Type I and 0, and also in those with additional clinically evident extra-thoracic disease e.g. in lymph node, eye and especially multiple systems. SACE also reflected clinical activity with levels being statistically significantly greater in those patients assessed as having active disease, although 7.9 per cent of these had normal levels. Our observations indicate that SACE levels correlate well with disease activity longitudinally, both in relation to spontaneous remission and steroid therapy, and are thus helpful in patient management.