Clinical Significance of Minor Elevation of Cardiac Troponin I

Chae Lim Jung; Sung Eun Cho; Ki Sook Hong

doi:10.3343/kjlm.2008.28.5.339

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Jung, Cho, and Hong: Clinical Significance of Minor Elevation of Cardiac Troponin I

Original Article

Korean J Leg Med 2008;28(5):339-345.

Published online: 14 February 2008

DOI: https://doi.org/10.3343/kjlm.2008.28.5.339

Clinical Significance of Minor Elevation of Cardiac Troponin I

Chae Lim Jung, M.D., Sung Eun Cho, M.D., Ki Sook Hong, M.D.

Department of Laboratory Medicine, School of Medicine, Ewha Womans University, Seoul, Korea

Received 13 December 20071 September 2008 Accepted 1 September 2008

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Cardiac troponin I (cTnI) is known as a sensitive and specific marker for myocardial ischemia. The purposes of this study are to establish cut-off values of cTnI for acute myocardial infarction (AMI) and to analyze clinical significance of minor elevation of cTnI.

Methods

Two hundred and four patients from whom cTnI was measured at Ewha Womans University Dongdaemun hospital from January to March, 2006 were enrolled in the study. cTnI was measured using Dimension RxL (Dade Behring, USA). The lower limit of detection (LLD), 10% CV value, 99th percentile of healthy individuals, and cut-off value for AMI by ROC curve analysis were determined.

Results

LLD, 10% CV value, and 99th percentile of cTnI were 0.00 ng/mL, 0.10 ng/mL, and 0.07 ng/mL, respectively. The cut-off value of peak cTnI for AMI by ROC curve analysis was 0.13 ng/mL with the sensitivity, specificity, and AUC of 90.9%, 87.7%, and 0.921, respectively. The peak value of cTnI of patients with ischemic heart disease (IHD) was higher than that of the patients without IHD (P<0.05). According to the above reference and cut-off values of the initial cTnI, patients were categorized into four groups; ≤0.05 ng/mL (group 1), 0.06-0.09 ng/mL (group 2), 0.10-0.59 ng/mL (group 3), ≥0.60 ng/mL (group 4), and compared frequencies of AMI, IHD, cardio vascular disease (CVD) and death after 1 month among groups. Frequencies of AMI, IHD, CVD, and death after 1 month were significantly increased as the cTnI concentrations were increased (P<0.05).

Conclusions

Minor elevation of cTnI value, even in group 3 was significantly associated with high incidence of AMI, IHD, CVD, and death rate after 1 month.

Keywords: 99th percentile of cTnI, 10% CV of cTnI, AMI cut-off value

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Fig. 1.

Total precision profile for cardiac troponin I (cTnI). The 10% CV value was 0.10 ng/mL.

Fig. 2.

ROC curve for cTnI in 204 patients with or without AMI.

Abbreviations: AUC, area under the curve; cTnI, cardiac troponin I; AMI, acute myocardial infarction.

Table 1.

The number of AMI by cTnI cut-off of 0.13 ng/mL

cTnI	AMI (N=33)	No AMI (N=171)
≥0.13 ng/mL	30	21
<0.13 ng/mL	3	150

Sensitivity, 90.9% (30/33); Specificity, 87.7% (150/171); Positive predictive value, 58.8% (30/51); Negative predictive value, 98.0% (150/153); Efficiency, 88.0%

Abbreviations: AMI, acute myocardial infarction; cTnI, cardiac troponin I.

Table 2.

Comparison of laboratory parameters between no IHD population and IHD population

	No IHD (N=140) Mean±SD	IHD (N=64) Mean±SD	P value^∗
Age (yr)	64.0±14.4	66.8±13.5	0.181
cTnI (ng/mL)
Initial value	0.06±0.06	1.67±8.27	0.123
Peak value^†	0.09±0.20	4.94±15.02	0.012
CK (U/L)	491.3±2846.1	395.6±952.8	0.793
CK-MB (ng/mL)	19.3±145.5	10.7±35.6	0.641
LD (U/L)	533.5±305.6	575.7±214.3	0.335
BNP (pg/mL)	237.5±662.7	538.8±975.4	0.077
Glucose (mg/dL)	140.0±61.9	175.7±142.1	0.062
BUN (mg/dL)^†	19.0±11.4	23.7±12.6	0.008
Cr (mg/dL)	1.34±4.50	1.34±1.63	0.999
CRP (mg/dL)	5.6±9.4	4.9±6.1	0.676
TG (mg/dL)	112.8±61.0	106.6±59.3	0.572
LDL-C (mg/dL)	114.2±47.4	101.2±46.3	0.241
HDL-C (mg/dL)^†	48.1±19.9	39.5±12.2	0.030
Total cholesterol (mg/dL)	178.5±49.7	166.1±45.3	0.156

^∗ Student t test;

^† P<0.05, statistically significant.

Abbreviations: IHD, ischemic heart disease; cTnI, cardiac troponin I CK, creatine kinase; LD, lactate dehydrogenase; BNP, B-type natriuretic peptide; CRP, C-reactive protein; BUN, blood urea nitrogen; Cr, creatinine; TG, triglyceride; LDL-C, low density lipoprotein-cholesterol; HDL-C, high density lipoprotein-cholesterol

Table 3.

Incidence of AMI, IHD, CVD, and death according to initial cTnI values

	cTnI (ng/mL)				P value^∗
	Group 1 ≤0.05 (N=142) [%, (N)]	Group 2 0.06-0.09 (N=22) [%, (N)]	Group 3 0.10-0.59 (N=30) [%, (N)]	Group 4 ≥0.60 (N=10) [%, (N)]	P value^∗
No AMI (N=171)	95.8 (136)	81.8 (18)	46.7 (14)	30.0 (3)	≤0.001
AMI (N=33)	4.2 (6)	18.2 (4)	53.3 (16)	70.0 (7)
No IHD (N=140)	81.0 (115)	68.2 (15)	30.0 (9)	10.0 (1)	≤0.001
IHD (N=64)	19.0 (27)	31.8 (7)	70.0 (21)	90.0 (9)
No CVD (N=116)	70.4 (100)	50.0 (11)	13.3 (4)	10.0 (1)	≤0.001
CVD (N=88)	29.6 (42)	50.0 (11)	86.7 (26)	90.0 (9)
Survival (N=134)	93.7 (104)	78.6 (11)	63.2 (12)	70.0 (7)	≤0.001
Death (N=20)	6.3 (7)	21.4 (3)	36.8 (7)	30.0 (3)

^∗ Statistically significant by chi-square analysis (P<0.05).

Abbreviations: AMI, acute myocardial infarction; IHD, ischemic heart disease; CVD, cardiovascular diseases.

Table 4.

Results of laboratory parameters according to initial cTnI values

	cTnI (ng/mL)				P value^∗
	Group 1 ≤0.05 (N=142) [%, (N)]	Group 2 0.06-0.09 (N=22) [%, (N)]	Group 3 0.10-0.59 (N=30) [%, (N)]	Group 4 ≥0.60 (N=10) [%, (N)]	P value^∗
CK (U/L)	169.6±474.6	194.2±251.3	1,974.2±6008.2	587.8±782.8	0.002
CK-MB (ng/mL)	1.7±6.6	3.4±3.9	86.1±308.9	48.3±81.5	≤0.001
LD (U/L)	504.8±247.1	548.3±249.8	696.8±393.0	648.5±148.4	≤0.001
BNP (pg/mL)	176.2±434.5	117.5±126.6	816.3±1,266.7	1,048.5±1,450.3	≤0.001
BUN (pg/mL)	19.0±10.7	20.2±17.0	24.8±12.3	27.9±9.7	0.003
Cr (mg/dL)	1.00±0.93	3.22±11.1	1.40±1.70	1.82±1.61	0.007

^∗ Statistically significant by Kruskall-Wallis test (P<0.05).

Abbreviations: cTnI, cardiac troponin I; CK, creatine kinase; LD, lactate dehydrogenase; BNP, B-type natriuretic peptide; BUN, blood urea nitrogen; Cr, creatinine.

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