How is sarcoidosis diagnosed
Is the serum angiotensin-converting enzyme (ACE) level useful for the diagnosis of sarcoidosis? What about serum lysozyme?
The serum ACE level is elevated in 40% to 90% of all patients with sarcoidosis. Elevations correlate with active pulmonary disease and can normalize with therapy. This enzyme is produced by epithelioid cells and alveolar macrophages at the periphery of granulomas in response to an ACE-inducing factor released by T-cells. Elevated ACE levels are not specific for sarcoidosis. Other diseases in which ACE levels can also be elevated include tuberculosis, coccidioidomycosis, Gaucher’s disease, hypersensitivity pneumonitis, silicosis, asbestosis, leprosy, hyperthyroidism, lung cancer, and diabetes mellitus. Additionally, there are genetic causes of ACE levels due to ACE gene polymorphisms. Therefore, an elevated ACE level may be supportive (especially if >2× upper limit of normal), but not diagnostic, of sarcoidosis. Of note, ACE inhibitors can suppress the serum ACE level.
The serum lysozyme level is elevated in 70% to 80% patients with sarcoidosis. It can be elevated when the ACE level is normal. Elevations correlate with the extent of sarcoid organ involvement and can normalize with therapy. This enzyme is secreted by monocytes and neutrophils. Elevated lysozyme levels are not specific for sarcoidosis as there are multiple other diseases that can cause an elevation. Similar to ACE levels, it can be supportive but not diagnostic of sarcoidosis .
