Angiotensin-Converting Enzyme (ACE)
Last updated: October 8, 2014
CPT Code: 82164
Description: Angiotensin-converting enzyme (ACE) catalyzes the conversion of angiotensin I to the potent vasopressor angiotensin II. ACE also inactivates the vasodilator bradykinin. Although it is produced primarily by endothelial and epithelial cells, ACE may also be synthesized in substantial quantities by activated macrophages in some pathologic conditions such as sarcoidosis.
Method: ACE is measured by bioassay; for example, an inhibitor-binding assay. Normal values may vary, and results must be interpreted according to laboratory standards.
Increased in: ACE is a test of low sensitivity and poor specificity. Elevated serum ACE levels are often associated with sarcoidosis. Although ACE levels are elevated in approximately 80% of patients with active pulmonary sarcoidosis, it may not be increased with extrapulmonary manifestations of sarcoid. Increased serum ACE levels may also be found in conditions such as interstitial lung disease of various etiologies (e.g., asbestosis, silicosis), hematologic malignancies (e.g., Hodgkin’s disease), endocrine diseases (e.g., hyperthyroidism and diabetes mellitus), and infections (e.g., leprosy, tuberculosis). Again, its important to note that patients with sarcoidosis may have normal serum ACE levels, depending on the organ involvement and extent and activity of disease. Also, although ACE levels have been reported to decrease after successful treatment of patients with sarcoidosis, this is not universally true. Thus, serum ACE levels must be interpreted carefully in sarcoidosis and those suspected of having sarcoidosis. When making a sarcoid diagnosis, biopsy evidence of noncaseating granuloma is more specific and reliable than ACE elevations. Decreased serum levels of ACE have been suggested to indicate endothelial injury (e.g., in patients with scleroderma).
ACE has also been measured in fluids other than serum, including cerebrospinal fluid (CSF) and bronchoalveolar lavage fluid. Although suggested to be of diagnostic utility (e.g., increased ACE levels in the CSF suggesting neurosarcoidosis), interpretation of results of these tests is somewhat controversial. Until the utility of ACE in these exceptoinal situations is established, it is best considered a research tool.
Confounding Factors: Factors that affect ACE levels include storage temperature, and samples kept frozen overnight or longer may have spuriously high values when tested.
Cost: $40–90.
BIBLIOGRAPHY
Lawrence EC. Serial changes in markers of disease activity with corticosteroid treatment in sarcoidosis. Am J Med 1983;74:747–756. PMID:6301276
