Association Between PET/CT Metabolic Parameters and Serum ACE and Calcium Levels in Sarcoidosis

Background: Sarcoidosis is a multisystem inflammatory disorder characterized by non-caseating granulomas, most commonly affecting the lungs and intrathoracic lymph nodes. Angiotensin-converting enzyme (ACE) levels and calcium abnormalities are recognized biomarkers, while ^18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) is increasingly used to assess disease activity. However, neither provides sufficient diagnostic accuracy alone. Therefore, this study aimed to investigate the relationship between FDG-PET/CT metabolic findings and serum ACE and calcium (Ca²⁺) levels as surrogate indicators of inflammatory metabolic intensity in sarcoidosis. Methods: In this retrospective single-center study, 127 patients with pulmonary sarcoidosis who underwent PET/CT at diagnosis were evaluated. Demographic and clinical data, ACE, and Ca²⁺ levels were recorded. FDG uptake in mediastinal, pulmonary, and extrapulmonary sites was analyzed, and correlations with biomarkers were assessed. Results: The cohort included 89 females (70.1%) and 38 males (29.9%), mean age 51.3 ± 11.9 years. FDG uptake was most frequent in mediastinal lymph nodes (84.3%) and lung parenchyma (40.9%). ACE levels correlated weakly with total SUVmax (r = 0.214, p = 0.019). Calcium levels correlated with extrapulmonary SUVmax (r = 0.327, p = 0.001) and were higher in patients with extrapulmonary involvement (p = 0.045). No associations were found between symptom presence and biomarkers or SUVmax values. Conclusions: FDG-PET/CT metabolic parameters, particularly total and extrapulmonary SUVmax, demonstrated modest yet statistically significant associations with ACE and calcium levels. These findings suggest that a combined biomarker-imaging approach may provide complementary information regarding inflammatory metabolic intensity and systemic involvement; however, the results should be interpreted as exploratory and require validation in prospective studies.