Angiotensin Converting Enzyme, Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Angiotensin converting enzyme (ACE) participates in the renin cascade in response to hypovolemia. Its peptidase action on the decapeptide angiotensinogen I results in the hydrolysis of a terminal histidyl leucine dipeptide and the formation of the octapeptide angiotensin II, a potent vasoconstrictor that increases blood pressure.
The primary source of ACE is the endothelium of the lung. ACE activity is increased in sarcoidosis, a systemic granulomatous disease that commonly affects the lungs. In sarcoidosis, ACE is thought to be produced by epithelioid cells and macrophages of the granuloma.
Currently, it appears that ACE activity reflects the severity of sarcoidosis: 68% positivity in those with stage I sarcoidosis, 86% in stage II sarcoidosis, and 91% in stage III sarcoidosis. Serum ACE also appears to reflect the activity of the disease; there is a dramatic decrease in enzyme activity in some patients receiving prednisone.
Other conditions such as Gaucher disease, leprosy, untreated hyperthyroidism, psoriasis, premature infants with respiratory distress syndrome, adults with amyloidosis, and histoplasmosis have been associated with increased levels of ACE.
Evaluation of patients with suspected sarcoidosis
An elevation in the level of serum angiotensin converting enzyme (ACE), along with radiographic evidence of infiltrates or adenopathy and organ biopsies showing noncaseating epithelial granulomas is suggestive of a diagnosis of sarcoidosis.
Serum ACE is significantly higher in most (approximately 80%) patients with active sarcoidosis.
ACE is also elevated in a number of other diseases and in approximately 5% of the normal adult population.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Spinal fluid angiotensin converting enzyme (ACE) activity to aid the diagnosis of neurosarcoidosis has been reported; however, there is insufficient evidence to support ACE being used for this purpose.
Serum ACE is significantly reduced in patients on ACE inhibitors (eg, VASOTEC and captopril).
The reference interval for children and adolescents may be as much as 50% higher than specimens from adults.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =18 years: 8-53 U/L
The reference interval for pediatric patients may be up to 50% higher than that of adults.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Liebermann J: Elevation of serum angiotensin-converting-enzyme (ACE) level in sarcoidosis. Am J Med 1975;59:365-372
2. Rodriguez GE, Shin BC, Abernathy RS, Kendig EL Jr: Serum angiotensin-converting enzyme activity in normal children and in those with sarcoidosis. J Pediatr 1981;99:68-72
3. Personal observations from a Mayo pediatric normal range study using a manual method (Hana)
4. Maguire GA, Price CP: A continuous monitoring spectrophotometric method for the measurement of angiotensin-converting enzyme in human serum. Ann Clin Biochem 1985;22:204-210