Bicarbonate interference with chloride-ion-selective electrodes.

echocardiography. All attending phy-sicians/cardiologists were blinded to the BNP results. To determine the diagnostic accuracy of the two assays for CHF, we performed ROC plot analysis, and areas under the curve (AUC) were calculated for both BNP assays. Comparisons between AUC were assessed according to the method of Hanley and McNeil (10). Cutoff values for the two methods were determined at the 90% sensitivity criterion derived directly from the ROC curves. Statistical analysis for the clinical evaluation was performed with the MedCalc 7.2.1.0 package (MedCalc Software) and the software N (IDV). All probabilities were two-tailed, and P values Ͻ0.05 were regarded as statistically significant. Of the 100 patients enrolled in the clinical study, 49 were classified as having dyspnea attributable to CHF, and 51 were classified as having dys-pnea attributable to other reasons. The reasons for dyspnea in these 51 patients were as follows: chronic obstructive pulmonary disease (n ϭ 21), pneumonia (n ϭ 10), bronchitis/ asthma (n ϭ 5), malignancy of the lung (n ϭ 1), musculoskeletal chest pain (n ϭ 4), hypertension (n ϭ 2), cardiac troponin-negative ACS (n ϭ 2), tachycardia/arrhythmia (n ϭ 2), and other causes (n ϭ 4), such as pulmonary embolism, interstitial lung disease, or anemia. In distinguishing between patients with (n ϭ 49) and patients without CHF (n ϭ 51), the AUC (SE) were 0.938 (0.025) for the AxSYM BNP assay (95% CI, 0.872– 0.977) and 0.932 (0.027) for the ADVIA Centaur assay (95% CI, 0.863– 0.972; Fig. 1C). AUC were not significantly different for the two BNP assays [difference (SE) of AUC, 0.007 (0.006); 95% CI, Ϫ0.005 to 0.019; P ϭ 0.265]. A power calculation showed that the power of this analysis was Ͼ99%. On the basis of the ROC curves, the cutoff values with a 90% sensitivity for CHF were 137 ng/L for the AxSYM BNP method [95% CI for sensitivity, 78 –97%; spec-ificity, 78% (95% CI, 65– 89%)], and 110 ng/L for the ADVIA Centaur BNP method [95% CI for sensitivity, 78 –97%; specificity, 78% (95% CI, 65– 89%)]. In conclusion, we demonstrated a considerable proportional difference between results obtained with the AxSYM and ADVIA Centaur BNP assays. Given the limitations of low enrollments, our preliminary clinical study suggests that both assays provide comparable diagnostic information for the diagnosis of CHF in an emergency setting. Further studies are needed to clarify additional analytical issues concerning the AxSYM BNP assay (including …