Angiotensin-converting enzyme (ACE) blood test in sarcoidosis
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ACE Blood Test as a Diagnostic Marker in Sarcoidosis
The angiotensin-converting enzyme (ACE) blood test is commonly used in the evaluation of sarcoidosis, a granulomatous disease with varied clinical presentations. ACE is produced by granulomas, making it a potential marker for disease activity and diagnosis .
Sensitivity, Specificity, and Predictive Value of ACE in Sarcoidosis
Multiple studies show that while ACE levels are often elevated in patients with active sarcoidosis, the test has significant limitations. Sensitivity—the ability to correctly identify those with the disease—varies widely, with reported values ranging from about 41% to 78% in adults 2510. Specificity—the ability to correctly identify those without the disease—also varies, with values around 59% to 90% 2510. The positive predictive value (PPV) is generally low, meaning a high ACE level does not strongly confirm sarcoidosis, but the negative predictive value (NPV) is high, so a normal ACE level makes sarcoidosis less likely 2510.
Differentiating Active and Inactive Disease
ACE levels tend to be higher in active sarcoidosis compared to inactive disease, and corticosteroid treatment can lower ACE activity 14. However, the correlation between ACE levels and disease activity is not always consistent, and some studies found no significant difference in ACE levels between active and remission phases .
ACE in Comparison to Other Conditions
Elevated ACE is not specific to sarcoidosis and can be seen in other conditions such as non-Hodgkin’s lymphoma, cirrhosis, and interstitial lung disease 2710. This lack of specificity limits the test’s diagnostic utility, especially in populations with a high prevalence of these other diseases.
Use of ACE in Pediatric Sarcoidosis
In children, ACE levels are naturally higher than in adults, and reference ranges must be interpreted with caution. Studies show that elevated ACE is found in about 50% of late-onset childhood sarcoidosis, but high ACE levels are also common in healthy children and those with other conditions, making the test less reliable for diagnosis in pediatric populations .
ACE Levels in Different Biological Fluids
ACE can also be measured in bronchoalveolar lavage fluid and cerebrospinal fluid, which may provide additional information, especially in cases with pulmonary or neurological involvement. However, these tests are less commonly used and have their own limitations regarding sensitivity and specificity .
Considerations for Clinical Practice
While the ACE blood test can support the diagnosis of sarcoidosis and help monitor disease activity, it should not be used in isolation. The test is most useful for ruling out sarcoidosis when levels are normal, given its high negative predictive value 2510. However, a diagnosis of sarcoidosis should always be based on a combination of clinical, radiological, and histological findings, with ACE serving as a supplementary tool 389.
Conclusion
The ACE blood test is a helpful but imperfect tool in the diagnosis and management of sarcoidosis. Its main value lies in its high negative predictive value, helping to exclude sarcoidosis when levels are normal. However, due to its low specificity and variable sensitivity, elevated ACE alone is not sufficient for diagnosis, and results must be interpreted in the context of the overall clinical picture 2510.
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