Normal Plasma Levels of Cardiac Troponin I Measured by the High-Sensitivity Cardiac Troponin I Access Prototype Assay and the Impact on the Diagnosis of Myocardial Ischemia
Per Venge, MD, PhD*,*,
Nina Johnston, MD, PhD ,
Bertil Lindahl, MD, PhD, and
Stefan James, MD, PhD,
* Department of Medical Sciences, Clinical Chemistry, University of Uppsala, Uppsala, Sweden
Department of Cardiology, University of Uppsala, Uppsala, Sweden
Uppsala Clinical Research Centre, University of Uppsala, Uppsala, Sweden
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Figure 1 The Imprecision Profile of the High-Sensitivity cTnI Access Assay
The inset shows the profile with the x-axis truncated at 0.030 µg/l and also the estimated 10% and 20% coefficients of variation (CVs). The 95% confidence interval of the fitted line is shown. cTnI = cardiac troponin I.
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Figure 2 The Distribution Profile of cTnI in Healthy Subjects
(A) The distribution of cardiac troponin I (cTnI) levels in the seemingly healthy population. The x-axis was truncated at 0.030 µg/l. (B) All results from the seemingly healthy subjects divided by sex. No statistical differences were found between sexes.
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Figure 3 The 99th and 97.5th Percentile Levels of cTnI in Seemingly Healthy Subjects
(A) Data from subjects <60 years of age and divided by sex. (B) Data from subjects  60 years of age and divided by sex. No statistical differences between sexes were found in either of the 2 cohorts. The percentile levels were defined after exclusion of outliers. In subjects <60 years of age results >0.012 µg/l and in subjects 60 years of age results >0.028 µg/l were defined as outliers. Abbreviations as in Figure 1.
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Figure 4 cTnI Levels in Healthy Subjects and Patients With ACS
The comparison of cTnI levels in seemingly healthy subjects and in patients with the acute coronary syndrome (GUSTO IV [Global Utilization of Strategies To open Occluded arteries IV]). Results above 10 µg/l were assigned 10 µg/l. The difference in cTnI levels between the cohorts was highly significant (p < 0.0001). ACS = acute coronary syndrome; other abbreviations as in Figure 1.
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Figure 5 ROC Curve Analysis of cTnI Levels in Healthy Subjects and Patients With ACS
Receiver-operator characteristics (ROC) curve analysis of the discrimination of healthy subjects and subjects with the acute coronary syndrome (GUSTO IV). The ROC curve and 95% confidence interval are shown, as well as the sensitivity and specificity at the optimal discrimination level 0.0064 µg/l. Abbreviations as in Figures 1 and 4.
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Figure 6 cTnI Levels in Healthy Subjects and in Patients With ACS With cTnT Below or Above 0.03 µg/l
The comparison of cTnI levels in seemingly healthy subjects and in patients with the acute coronary syndrome (GUSTO IV) with cardiac troponin T (cTnT) below or above 0.03 µg/l. Results above 10 µg/l were assigned 10 µg/l. The difference in cTnI levels between the cohorts was highly significant (p < 0.0001) (analysis of variance) as were the differences between healthy subjects and either of the 2 GUSTO IV subsets (p < 0.0001). Abbreviations as in Figures 1 and 4.
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Figure 7 ROC Curve Analysis of cTnI Levels in Healthy Subjects and Patients With ACS With cTnT Below or Above 0.03 µg/l
ROC curve analysis of the discrimination of healthy subjects and subjects with the acute coronary syndrome (GUSTO IV) with cTnT levels below (left) or above (right) 0.03 µg/l. The ROC curve and 95% confidence interval are shown, as well as the sensitivities and specificities at the optimal discrimination levels of 0.0046 and 0.0164 µg/l, respectively. Abbreviations as in Figures 1, 4, and 6.
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