Seizure or Syncope: The Usefulness of Serum Laboratory Tests and Arterial Blood Gas Analysis for Making the Differential Diagnosis

ABSTRACT

PURPOSE: To determine whether analyte levels in serum laboratory tests and arterial blood gas analysis (ABGA) are helpful for differentiating between generalized seizures and syncope in the emergency department (ED). METHODS: Patients over 18 years old who presented to an ED of a tertiary care hospital with a transient loss of consciousness within 4 hours were selected to be in either the seizure (n=166) or syncope groups (n=168). After exclusion for criteria, we used ROC curves to determine AUC, optimal cut-off value, sensitivity, and specificity, depending on time (4 hour, 2 hour, 1 hour and 0.5 hour). We also did multivariate logistic regression. RESULTS: A total of 75 seizure group patients and 78 syncope group patients were studied. There were significant between group differences in total CO2 content, LDH, ammonia, pH, bicarbonate and lactate. AUC (area under the curve) values for blood tests were 0.720 (tCO2), 0.686 (LDH), 0.737 (ammonia), 0.798 (pH), 0.710 (bicarbonate) and 0.770 (lactate). All AUC values were increased as the time from symptoms to ED arrival was shortened (except for LDH). On multivariate logistic regression analysis, pH (OR=9.587, 95% CI, 2.573-35.723. p=0.001) and ammonia (OR=3.932, 95% CI, 1.324-11.613, p=0.014) were statistically significant independent predictive factors. CONCLUSION: Serum laboratory testing and ABGA, especially serum ammonia and arterial pH, may be helpful for differentiating between generalized seizure and syncope in patients who experience a transient loss of consciousness and who come to the ED within 4 hours after the appearance of symptoms. But further evaluation is needed.