Negative interference of bilirubin and hemoglobin in the MEIA troponin I assay but not in the MEIA CK-MB assay.

Troponin I is a sensitive and specific marker for the diagnosis of myocardial infarction. Several commercially available immunoassays measure the concentration of troponin I in serum. The microparticle enzyme immunoassay (MEIA) for troponin I (Abbott Laboratories, Abbott Park, IL) is widely used in clinical laboratories, including our hospital laboratory. We studied the effect of bilirubin and hemolysis on the MEIA for troponin I and compared our assay with a newly available chemiluminescent assay (CLIA) for troponin I (Bayer Diagnostics, Tarrytown, NY). We also measured CK-MB concentration using the MEIA CK-MB assay. One serum pool was prepared by combining several specimens of one patient with elevated troponin I and with a diagnosis of myocardial infarction. Other serum pools were prepared by combining sera with similar troponin I values. All serum pools showed normal bilirubin concentrations and had no hemolysis. Then we supplemented aliquots of serum pools with various concentrations of bilirubin (5.0, 10.0, 15.0, and 20.0 mg/dL). After supplementation, troponin I concentrations were measured again using the MEIA and CLIA. We observed a statistically significant decrease in troponin I concentration in the presence of bilirubin with the MEIA. For example, in serum pool 1, the troponin I concentration was 16.3 (bilirubin: 0.8 mg/dL). In the presence of 5.0, 10.0, 15.0 and 20.0 mg/dL of added bilirubin, the cardiac troponin I concentrations were 13.9, 13.4, 13.3 and 13.0 ng/ml respectively. We observed similar negative interference of bilirubin in troponin I measurement by the MEIA in other pools. The troponin I value decreased slightly (not statistically significant) in one pool and did not change in two other pools in the presence of bilirubin when we measured troponin I concentration using the CLIA. Interestingly, bilirubin did not interfere with the MEIA CK-MB assay. Moderate hemolysis did not have any effect on the troponin I assay using either the MEIA or CLIA. However, gross hemolysis (hemoglobin > 40 mg/dL) interfered with both assays for troponin I.