Evaluation of human serum albumin cobalt binding assay for the assessment of myocardial ischemia and myocardial infarction

Abstract

Background: Clinical diagnoses were correlated with results of a Co(II)-albumin binding assay in 167 patients treated at an emergency department of a health maintenance organization.

Methods: Patients were evaluated as being nonischemic or potentially ischemic through standard coronary disease indicators [creatine kinase (CK), CK-MB, cardiac troponin I, and electrocardiographic findings] and were tested by a Co(II)-albumin binding assay. Samples were tested anonymously, and the study was double-blinded. The sensitivity and specificity of this assay for the detection of ischemia were evaluated by ROC curve analysis. Known Co(II) binding sites on albumin were analyzed by N-terminal amino acid sequencing.

Results: The mean absorbance units (ABSU) +/- 2 SD for non-myocardial ischemic and myocardial ischemic individuals measured at 470 nm were 0.43 +/- 0.10 and 0.63 +/- 0.25, respectively (P <0.0001). The area under the ROC curve was 0.95 [95% confidence interval (CI), 0.92-0.99], and at a cutoff value of 0.50 ABSU, sensitivity and specificity were 88% (78-94%) and 94% (86-98%), respectively, suggesting a high distinction between the two groups. When we compared non-acute myocardial infarction (AMI) and AMI ischemic individuals, the area under the ROC curve was 0.66 (95% CI, 0.53-0.79) and was considered a poor discriminator between these two groups. N-Terminal amino acid sequencing data for purified albumin showed normal amino acid residues for six of seven high-ABSU (> or =0.70) individuals and one nonischemic individual tested. However, only one individual with a high ABSU (0.80) had two missing amino acid residues (DA) from the N-terminal region. Clinical diagnosis for this patient did not reveal an ischemic event.

Conclusions: The Co(II)-albumin binding test may serve as a useful diagnostic tool in emergency facilities for the assessment of myocardial ischemia. High and low ABSU were associated with myocardial ischemic individuals and non-myocardial ischemic individuals, respectively. However, the Co(II)-albumin binding was a poor discriminator between ischemic individuals with and without MI.