Relationship Between Salivary and Serum Cardiac Troponin I in Patients Undergoing Cardiac Surgery: A Prospective Longitudinal Observational Study

Background/Objectives: Cardiac troponin I (TnI) is the reference biomarker for detecting myocardial injury. Saliva has recently emerged as a potential non-invasive diagnostic fluid; however, evidence regarding the clinical utility of salivary TnI remains limited. This study aimed to compare serum and salivary TnI concentrations in patients undergoing cardiac surgery and to evaluate their relationship during the perioperative period. Methods: A prospective longitudinal observational study included 54 adult patients undergoing elective cardiac surgery with cardiopulmonary bypass and cardioplegic arrest. Serum and unstimulated saliva samples were collected 18–20 h before surgery, 18–20 h after surgery, and 42–44 h after surgery. TnI concentrations were measured using a high-sensitivity chemiluminescent immunoassay. Salivary pH, salivary flow rate, renal function, and fluid balance were also recorded. Results: Significant perioperative changes in TnI concentrations were observed in both serum and saliva (p < 0.001). Median salivary TnI increased from 3.0 ng/L preoperatively to 9.2 ng/L at 18–20 h postoperatively and decreased to 6.4 ng/L at 42–44 h. Median serum TnI increased from 10.2 ng/L to 2593.1 ng/L and subsequently decreased to 1204.5 ng/L. Despite similar temporal trends, no significant correlation was found between serum and salivary TnI concentrations at any time point. Ischemic time was positively associated with postoperative serum TnI concentrations (ρ = 0.347, p = 0.01), whereas no such association was observed for salivary TnI. Salivary TnI concentrations were not significantly associated with salivary flow rate or pH. Conclusions: Salivary TnI concentrations increased significantly following cardiac surgery, indicating measurable perioperative changes within the salivary compartment. However, no significant association was observed between salivary and serum TnI concentrations under the conditions investigated in this study. Therefore, the present findings do not support the use of salivary TnI as a surrogate marker of circulating troponin concentrations. Further analytical validation of high-sensitivity troponin assays in saliva and additional clinical studies are required before definitive conclusions regarding the biological significance and potential clinical utility of salivary troponin measurements can be made.