For a study, researchers sought to examine the diagnostic utility of End-tidal carbon dioxide (ETCO2) measured non-invasively at the bedside to differentiate between unstable angina pectoris (UAP) & non-cardiac chest pain in patients who presented to the emergency department with chest pain without a history of cardiac pathology.

The patients in the clinical study were those who presented with chest pain to the emergency room of a tertiary hospital. It was a prospective case-control study. The patients were split into 2 groups after the inclusion and exclusion criteria were assessed: 62 patients had UAP and 62 had non-cardiac chest pain. To establish the cut-off in diagnostic value measurements, Receiver Operating Characteristic (ROC) analysis was used. The odds ratio of ETCO2 (including 95% CIs) was calculated using univariate binary logistic regression analysis for UAP prediction.

With 35 cut-offs identified, ETCO2 provided strong diagnostic power for identifying UAP (AUC: 0.84, 95% Cl: 0.76-0.90, P< 0.001). When ETCO2, which influences both UAP and non-cardiac chest pain, was assessed, an ETCO2 of 35 was statistically significant and is 9.74 times more frequent in UAP patients than in non-cardiac chest pain patients.

It may be suggested that ETCO2, a non-invasive parameter that can be tested right away at the patient’s bedside, be used as a possible biomarker to distinguish patients with UAP from those who are experiencing non-cardiac chest pain.