Objective: To evaluate the extent to which oximetry, spirometry and dyspnea scoring can reflect hypoxemia and hypercapnia among patients admitted to the emergency department (ED) with acute exacerbations of chronic obstructive pulmonary disease. Subjects and Methods: Spirometry, oxygen saturation by pulse oximetry (SpO(2)), arterial blood gas analysis and dyspnea scoring assessments were made in the ED. Correlations of these parameters were evaluated by means of Pearson's test. Pulse oximetry cutoff values to express hypoxemia were demonstrated by receiver operating characteristic (ROC) curves. Results: 76 patients with a mean age of 68.0 years were included in the study. Mean spirometric values, expressed as percentages of predicted values, were forced expiratory volume in 1 s ( FEV1) = 23.1 +/- 9%; forced vital capacity (FVC) = 32.8 +/- 11%, and mean FEV1/FVC = 72.4 +/- 21.6%. While there was a positive correlation between the SpO(2), SaO(2) and PaO2 values (r = 0.91 and 0.80, respectively), a negative correlation ( r = -0.74) was observed between PaCO2 and SpO(2). In determining hypoxemia, both SpO2 and FEV1 were sensitive (83.9 and 90.3%, respectively) while dyspnea scoring was the most sensitive (93.5%). In the evaluation by means of an ROC curve, a saturation of 88.5% for the pulse oximeter was the best cutoff value to reflect hypoxemia (sensitivity 95.6%, specificity 80.6%). Conclusion: SpO(2) alone appears to be as highly specific as a combination of other tests in the evaluation of hypoxemia. A cutoff value for SpO(2) of <= 88.5% is proposed as a criterion in screening for hypoxemia. Copyright (c) 2007 S. Karger AG, Basel.