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.