Serum angiotensin-converting enzyme levels indicating early sarcoidosis diagnosis and immunosuppressive therapy efficacy.

Aims: This study aimed to determine the new cut-off value of serum angiotensin-converting enzyme (ACE) levels for detecting patients with sarcoidosis and to examine the change in ACE levels after the initiation of immunosuppressive therapy.

Methods And Results: We retrospectively examined patients in whom serum ACE levels were measured for suspected sarcoidosis between 2009 and 2020 in our institution. For patients diagnosed with sarcoidosis, changes in ACE levels were also observed. Of the 3781 patients (51.1% men, 60.1 ± 17.0 years old), 477 were excluded for taking ACE inhibitors and/or immunosuppression agents or those with any diseases affecting serum ACE levels. In 3304 patients including 215 with sarcoidosis, serum ACE levels were 19.6 IU/L [interquartile range, 15.1-31.5] in patients with sarcoidosis and 10.7 [8.4-16.5] in those without sarcoidosis (P < 0.01), and the best cut-off value was 14.7 IU/L with 0.865 of the area under the curves. Compared with the current ACE cut-off of 21.4, the sensitivity improved from 42.3 to 78.1 at the new cut-off, although specificity slightly decreased from 98.6 to 81.7. The ACE level significantly decreased more in those with immunosuppression therapy than in those without it (P for interaction <0.01), although it decreased in both groups (P < 0.01).

Conclusions: Because the sensitivity for detecting sarcoidosis is comparatively low at the current standard value, further examinations are needed for patients suspected of sarcoidosis with relatively high ACE levels in the normal range. In patients with sarcoidosis, ACE levels decreased after the initiation of immunosuppression therapy.