Diagnostic Value of Cardiac Creatin Kinase and Cardiac Troponin I Measurement in Suspected Myocardial Infarction Patients

³ Cardiovascular Research Center, Hamadan University of Medical Sciences, Hamadan, Iran

⁴ Department of Social Medicine, Hamadan University of Medical Sciences, Hamadan, Iran

*Corresponding author: Farnaz Fariba, Department of Cardiology, School of Medicine, Cardiovascular Research Center, Hamadan University of Medical Sciences, Hamadan, Iran. Email: farnaz.fariba@gmail.com

EXTENDED ABSTRACT

Background

Myocardial infarction (MI) is a major manifestation of coronary artery disease [1], and its diagnosis relies on clinical evaluation together with electrocardiographic findings and biochemical markers. The article notes that electrocardiography alone may have insufficient sensitivity and specificity and that a normal electrocardiogram does not exclude MI. Creatine kinase MB (CK-MB) has long been used as a marker of cardiac injury, but increased CK-MB is not fully specific for myocardial damage [2,3]. Cardiac troponin I (cTnI), a regulatory protein specific to cardiac muscle, has been reported to have greater clinical sensitivity than CK-MB for acute myocardial injury and may remain detectable for several days after injury [4,6-11]. Although previous studies cited in the article generally favored cardiac troponin over CK-MB [8-11], the authors stated that a large Iranian comparison of the diagnostic performance of these markers in patients suspected of acute coronary syndrome had not been conducted. Therefore, this study aimed to assess the diagnostic value and accuracy of cTnI in patients suspected of MI and to compare its sensitivity, specificity, predictive values, and overall diagnostic accuracy with those of CK-MB.

Methods

This descriptive study reviewed the medical records of 453 patients older than 18 years who presented with chest pain to the emergency department of Farshchian Hospital, Hamadan, in 2017 and were considered by the treating physician to have suspected acute coronary syndrome. Records were eligible when the initial diagnostic assessment included serial electrocardiography and serum cTnI and CK-MB measurements at presentation (0 hour), one hour after presentation, and six hours after presentation to confirm or exclude MI. Patients were excluded if they had experienced a seizure during the preceding three days, had recently received an intramuscular injection, had chronic renal failure, had recently undergone surgery, or had recently sustained skeletal injury. For cTnI, the article describes a rapid qualitative chromatographic immunoassay performed using the Vidas system. A 70 µL whole-blood sample was added to the test cassette; a colored line in the test region indicated the presence of cTnI, whereas a control line verified adequate sample application. The laboratory reference value for cTnI was reported as <0.01 µg/L. CK-MB was measured in serum by an immunoinhibition method using a BT3500 autoanalyzer and a Pars Azmoon kit, with values <26 U/L considered normal and values of 26 U/L or higher treated as positive in the reported diagnostic table. Final MI status was obtained from the documented clinical assessment in the medical records. Diagnostic performance was evaluated by calculating sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy for each biomarker. The qualitative agreement between cTnI and CK-MB results was also evaluated with a kappa test. Data were analyzed using SPSS version 21 and summarized with mean±standard deviation for quantitative variables and frequency and percentage for qualitative variables. The study received ethics approval from Hamadan University of Medical Sciences (IR.UMSHA.REC.1397.073).

Results

Among the 453 patients with suspected acute coronary syndrome, 360 (79%) had a final diagnosis of MI and 93 (21%) did not have MI. Overall, 301 patients (66.45%) were men and 152 (33.55%) were women. Mean age was 65.28±14.38 years, with an age range of 23-97 years; the most frequent age group was 60-65 years. The recorded MI categories were NSTE MI in 179 patients, STE MI in 72, MI in 30, Extensive MI in 21, Inf MI in 20, Late MI in 16, Ant MI in 11, Envolved MI in 6, Recent MI in 4, and Active MI in 1, together accounting for the 360 patients with MI.

Table 1. Frequency of agreement between qualitative cTnI and CK-MB results in the study patients.

For cTnI, 348 of the 360 patients with MI had a positive test, whereas 12 had a negative result. None of the 93 patients without MI had a positive cTnI result, and all 93 were classified as negative. On this basis, cTnI had a sensitivity of 96.67%, specificity of 100%, positive predictive value (PPV) of 100%, negative predictive value (NPV) of 88.57%, and accuracy of 97.35% for differentiating MI from non-MI.

In contrast, CK-MB was positive in 292 of 360 patients with MI and negative in 68. Among the 93 patients without MI, Table 3 reported 81 positive CK-MB results and 12 negative results.

The corresponding diagnostic indices for CK-MB were sensitivity 81.11%, specificity 12.90%, PPV 78.28%, NPV 15%, and accuracy 67.08%. Thus, the reported sensitivity, specificity, PPV, NPV, and diagnostic accuracy were all higher for cTnI than for CK-MB.

Table 4. Sensitivity, specificity, predictive values, and accuracy of troponin I and CK-MB for the final diagnosis of MI.

Across the entire sample, the qualitative biomarker cross-tabulation reported 348 cTnI-positive and 105 cTnI-negative results, compared with 373 CK-MB-positive and 80 CK-MB-negative results. Specifically, 282 patients were positive for both cTnI and CK-MB, 66 had positive cTnI with negative CK-MB, 91 had negative cTnI with positive CK-MB, and 14 were negative for both tests. The kappa analysis did not demonstrate a statistically significant association between the qualitative cTnI and CK-MB results (P=0.185). No confidence intervals or effect-size estimates for the diagnostic indices were reported in the article. Overall, the detailed diagnostic-performance results favored cTnI over CK-MB for identifying MI in this study population.

Conclusion

In patients presenting with chest pain and suspected acute coronary syndrome, cTnI demonstrated higher sensitivity, specificity, predictive performance, and overall accuracy for MI than CK-MB. Troponin I correctly identified 348 of 360 patients with MI and produced no false-positive results among the 93 patients without MI, whereas CK-MB showed substantially lower specificity and accuracy. The authors therefore concluded that cardiac troponin is a better marker than CK-MB for identifying patients with myocardial infarction. They further stated that simultaneous performance of both tests may add cost and delay laboratory reporting without materially improving clinical decision-making. Accordingly, within the population and diagnostic procedures evaluated in this study, cTnI provided the more favorable diagnostic profile. The conclusion should remain limited to the study population and the testing approach described in the article.

Keywords: Cardiac Marker, Creatine Kinase MB Form, Myocardial Infarction, Troponin I

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