VALUE OF SERUM ASSAYS OF COPEPTIN VERSUS TROPONIN I AT ADMISSION FOR EARLY DIAGNOSIS OF ACUTE CORONARY SYNDROME

VALUE OF SERUM ASSAYS OF COPEPTIN VERSUS TROPONIN I AT ADMISSION FOR EARLY DIAGNOSIS OF ACUTE CORONARY SYNDROME

By

Abdel Wahab Mohammed  Lotfy*;  Nagwa abd El-Ghaffar Mohamed**; Abdelaziz  Rezk Sheridah*; Mahmoud Haddad Hemida*

and Mahmoud Mohamed Abdelshakour*

Internal Medicine Departments, Faculty of Medicine - Al Azhar University*

and National Research Center**

ABSTRACT

Background: The major drawback of current troponin assays is sensitivity deficit at presentation due to delayed release of circulating levels. Therefore, acute myocardial infarction (AMI) exclusion requires prolonged period of monitoring for 6 to 9 hours and serial blood sampling, the grey zone for troponin elevation, which consequently leads to overcrowding in the emergency department and increases the associated cost every year. As a result, novel biomarkers are continuously in development. A particularly interesting observation is the response of circulating copeptin levels as a result of an acute myocardial infarction.

Objective: Comparing the value of serum copeptin assays to serum troponin I for early diagnosis of acute coronary syndrome.

Patients and methods:  A prospective non- randomized study will be conducted over 45 patients in National heart institute (NHI). All of the patients were above 40 years old, presented to the emergency department  (ED) within 12 hours of symptom onset of acute chest pain suggestive of acute coronary syndrome. After informed consent and permission from the local administrative authority, all patients were subjected to a thorough history taking, examination, 12- lead ECG monitoring, coronary angiography and echocardiographic assessment. In addition to the routine laboratory investigations. Cardiac troponin I and copeptin were assayed from venous blood samples obtained at admission, then 6 hours later. Based on clinical picture, ECG findings, serial troponin I assays, coronary angiography and echocardiographic findings all of the patients were divided into 3 groups: 

1. ST-segment elevation of myocardial infarction (STEMI).

2. Non ST- segment elevation of  myocardial infarction (NSTEMI) .

3. Unstable angina (UA).

Results: The admission values of copeptin was significantly different.  At a cutoff value of 30.5 pmol/l, AMI can be diagnosed with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and accuracy 100%. The admission values for troponin I was significantly different. At cutoff value of 0.23 ng/ ml AMI can be diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%. The 6 hours-later copeptin values were also significantly different.  AMI was diagnosed at cutoff value of 32.2 pmol/l with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and 100% accuracy. The 6 hours later values of troponin I  were significantly different. At cutoff value of 0.23 ng/ml, AMI was diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%.

Conclusion: The current study provided evidence that measurement of serum copeptin was better than troponin I for early diagnosis of acute myocardial infarction, but could not evaluate the value of copeptin in UA diagnosis versus non -ischemic causes of chest pain.

Keywords: Copeptin, acute coronary syndrome, troponin I, NSTEMI.

INTRODUCTION

     Chest pain was the second leading reason for emergency department (ED) visits in USA. A principal hospital discharge diagnosis of ischemic heart disease was assigned to 2.9 % of all ED visits. Even though not all chest pain patients will cause the treating physician to suspect AMI and even though AMI also needs to be suspected in many patients with symptoms other than chest pain. These numbers emphasize the clinical need for an early and fast rule-out of AMI. Under the current standard process of evaluating these patients, a minimum stay of between 3 and 9 hours is mandatory (Smaradottir  et al., 2017).

     Given that the vast number of these stays are ultimately unnecessary, personnel and space resources are wasted in the ED and patients are left to wait until the possible diagnosis of a “heart attack” has dissolved. In times of increasing ED crowding, which has been shown to negatively impact patient outcome, this process is basically unacceptable (Mockel et al., 2013)

     The diagnosis of acute myocardial infarction is based on symptoms, signs and findings on the electrocardiogram, but in some patients these findings are non-diagnostic. In this patient population, the use of cardiac biomarker which indicates cardiac tissue necrosis - of which troponin and creatine kinase isoenzyme (CKMB) are preferred markers - play a pivotal role. These biomarkers allow for rule in of AMI within 3 hours after presentation in majority of patients and offer the opportunity to initiate an  appropriate and evidence based treatment strategy (Vargas  et al., 2016).

    The major drawback of current troponin assays is sensitivity deficit at presentation due to delayed release of circulating levels. The vast majority of patients presenting to the emergency department with chest pain turn out not to have AMI. One quarter to one third of patients with AMI present without significant ECG changes indicative of ischemia. Therefore, ECG is of little help to rule out AMI (Deedwania et al., 2013).

    As a result, and due to the lack of a completely early and accurate biomarker that effectively rule in and/or out AMI, novel biomarkers are continuously in development. A particularly interesting observation is the response of circulating copeptin levels as a result of an acute myocardial infarction (Keller et al., 2009 and Pentighini, 2015).

     The incremental value of copeptin to troponin was first elucidated by Reichilin et al. (2009a).  Keller et al. (2009) confirmed these findings in a chest pain unit population. They reported the results of serial blood sampling in a subgroup of patients who presented within 2 hours after symptom onset to illustrate the complementary kinetics of troponin, the concentration of which increased 6 hours after admission, and copeptin, the concentration of which decreased during the first 6 hours after a peak at presentation, in patients with AMI (Keller et al., 2009 and Reichlin et al., 2009a).

    (CHOPIN), the largest multi-center trial of this type, confirm that the combination of a negative troponin and negative copeptin on presentation allows the rule out of AMI for 58% patients with >99.2% negative predictive value. In addition, copeptin value (>14 pmol/l) was able to detect greater numbers of patient with acute myocardial infarction and non-ST-elevation myocardial infarction at presentation when cardiac troponin was undetectable (Maisel et al., 2013).

PATIENTS AND METHODS

     A prospective, non- randomized study was conducted over 45 patients in National heart institute (NHI) from Oct. 2014 to Oct. 2016.  All of the patients were above 40 years old, presented to the ED within 12 hours of symptom onset of acute chest pain suggestive of acute coronary syndrome. After informed consents and permission from the local administrative authority, all patients were subjected to a thorough history taking, examination, 12- lead ECG monitoring, coronary angiography and echocardio-graphic assessment. In addition to the routine laboratory investigations, cardiac troponin I and copeptin were assayed from venous blood samples obtained at admission, then 6 hours later.

     Based on clinical picture, ECG findings, serial troponin I assays, coronary angiography and echocardiographic findings all of the patients will be divided into 3 groups: 

1. ST-segment elevation of myocardial infarction.

2. Non-ST- segment elevation of myocar-dial infarction.

3. Unstable angina.

Exclusion criteria:

     1-Patients with heart failure, myocar-ditis and pericarditis 2-Sepsis and septic shock 3-Lower respiratory tract infection 4-Diabetes insipidus 5- Recent cerebro-vascular stroke 6-Hyponatremia 7-Malig-nancy  8-Chronic renal failure

    The concentration of copeptin was measured by the BRAHMS copeptin-us immune-luminometric assay on the KRYPTOR Compact Plus system (Thermo Fisher Scientific). The detection limit, as described by the manufacturer was signified as being 0.9 pmol/L, and the lowest concentration measurable with a coefficient of variation (CV) <10% has been reported <4 pmol/L. The direct measuring range was 0.9–500 pmol/L. Blood samples for copeptin were centrifuged, and plasma was frozen at −80°C. Copeptin measurement was performed at the end of the study recruitment, blinded to the final diagnosis. The concentration of troponin I was measured directly after withdrawal using the second-generation AxSYM Troponin-I ADV assay on the Abbott AxSym System. The analytical sensitivity of the assay was 0.02 ng/ml with a 10% coefficient of variation at 0.16 ng/ml. Two samples were used, i.e. on admission (A) and 6 - hours later(B).

Statistical analysis: Biomarkers were treated as categorical variables. Differences between the groups were examined with their means and SD in each group and, whenever we found a significant differences, ANOVA and Tukey's tests were done as appropriate. Paired samples test was used to determine the paired differences between the first and second biomarker assays. The tests were done for samples (A) for troponin I and copeptin together, then for samples (B) together and then we compared the general copeptin and troponin I values. Receiver operating characteristic (ROC) curve was used to determine the sensitivity, specificity, negative predictive values (NPV) and positive predictive values (PPV) for the biomarkers, and optimal cutoff values for both troponin and copeptin.  For all tests a p-value <0.05 was regarded as statistically significant.

RESULTS

- The admission values of copeptinwere significantly different (P value < 0.001) in:  STEMI versus UA,  NSTEMI versus UA  and in STEMI versus NSTEMI (Table 1).

Table (1): Ranges of copeptin (pmol/l) values in patient groups.

 -Paired sample test showed significant increase in copeptin level after 6hs in all study groups. A=value at admission, B =value 6h later, C=copeptin, G=groups.

      Tukey's  test showed significant difference in copeptin in STEMI versus UA,  in STEMI versus NSTEMI and in STEMI versus NSTEMI, either at admission or 6h later S=STEMI, N=NSTEMI, U=UA, A= copeptin at admission, B= copeptin 6h later (Table 2).

     ANOVA test showed significant difference among the study groups in copeptin either at admission or 6h later.

Table(2): ANOVA and TUKEY’s evaluating copeptin values in patient groups.

- At a cutoff value of 30.5 pmol/l, AMI was diagnosed with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and accuracy 100% (Table 3).

Table (3): Values of receiver operator curve (ROC) of copeptin at admission: cutoff, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy.

- At a copeptin cutoff value of 32.2 pmol/l, AMI was diagnosed 6 hs after admission with sensitivity 100, specificity 100, PPV 100, NPV 100 and accuracy of 100% (Table 4).

Table (4): Values of receiver operator characteristic (ROC) of copeptin 6 hours later: cutoff, sensitivity, specificity, (PPV), (NPV), and accuracy.

- The admission values for troponin Iwere significantly different (P value < 0.001) in STEMI versus UA and also, in NSTEMI versus UA (Table 6).

Table (5): Ranges of troponin values (ng/ml) at admission (A) or 6h later (B).

Paired sample test showed significant increase in troponin I level after 6hs in STEMI and NSTEMI.

- ANOVA test showed significant diffe-rence among the study groups in troponin I level either at admission or 6h later. Tukey’s test showed significant difference in troponin I level in STEMI versus UA and in NSTEMI versus UA, either at admission or 6h later, but no significant difference in STEMI versus NSTEMI (Table 6).

Table (6): ANOVA and Tukey’s tests evaluating troponin I values: (A)=at admission, (B)=6h later, (T)=Troponin I, (G)=Groups.

- At admission at a cutoff value of 0.23 ng/ml AMI was diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%  (Table 7).

Table (7): ROC of troponin I value at admission: cutoff, sensitivity, specificity, (PPV), (NPV), and accuracy.

- The 6 hours later values of troponin I values were significantly different  (P <0.001) in STEMI versus UA and in NSTEMI versus UA (table 6). At cutoff value of 0.23 ng/ml AMI was diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98% (Table 8).

Table (8): Cutoff value, PPV, NPV, sensitivity, specificity and accuracy of troponin I value 6 hours later.

- The overall admission and 6 hours later values for copeptin were also signifi-cantly different, and AMI was diagnosed at cutoff value of 30.49 pmol/l with 100 sensitivity, 100 specificity, 100 PPV, 100 NPV and 100% accuracy.

- The overall admission and 6 hours later values for troponin I were also significantly different as before, and at a cutoff value of 0.22 ng/ml AMI was diagnosed with 93.33 sensitivity, 100 specificity, 100 PPV, 88.2 NPV and accuracy 98%.

- This study revealed that copeptin alone was better than troponin I for diagnosis of AMI, and this was in accordance with the studies done before. The optimal cutoff value of copeptin for AMI diagnosis in our study, being 30.49 pmol/l.

DISCUSSION

    This study revealed that copeptin alone was better than troponin I  for diagnosis of AMI, and this was in accordance with the studies done before. The optimal cutoff value of copeptin for AMI diagnosis in our study, being 30.49 pmol/l, is different from other studies that used cutoff values of (9 pmol/L, 14 pmol/L, 20 pmol/L, and 24 pmol/L). Lipinski et al. (2014) demonstrated that Copeptin shows only low specificity for myocardial damage. Accordingly, the positive predictive value  (PPV) for AMI of copeptin alone is thought  to be unacceptably low.  The first  studies investigating  the diagnostic value of copeptin for AMI showed a very low PPV for AMI.  For instance, Reichlin et al. (2009a) calculated the PPV of copeptin for AMI diagnosis for different cut-off concentrations. In their study, the PPV of copeptin ranged between 34.9% and 57.9%. (Lipinski et al., 2014 and Reichlin et al., 2009a).

    Copeptin is a biomarker of AMI, not the acute coronary syndrome. Reichlin et al. (2009b) reported no significant difference in copeptin concentration between UA patients and patients with non- ischemic causes of chest pain and attributes this to that UA does not cause sufficient endogenous stress for vasopressin release. On the other hand, Johan et al. 2013 reported that copeptin values are higher in the UA patients compared to the non-ACS group, but this finding was statistically insignificant. The current study revealed that copeptin values in UA were significantly different from both STEMI and NSTEMI, but evaluation of copeptin values in UA compared to non- ACS was not possible in our study as all of our patients have ACS, and no patients of chest pain due to non- ischemic causes. Other studies should be warranted to highlight this issue (Reichlin et al., 2009b and Johan et al., 2013).

    The current study showed a significant difference between copeptin values in STEMI and NSTEMI  in comparison to troponin I that showed an insignificant difference between them. These results were in consistence with the other studies (Vargas  et al. 2016).                                                                                                        

    Unlike the other studies, in the current study, copeptin was tending to have a statistically significant increase from admission to 6 hours later, and this occurred in all patient groups including UA. The other studies reported that maximal serum values were one hour after the onset of chest pain then decreased gradually to reach a plateau one to two days later. The pattern of release was more questionable in UA, since the increase in copeptin values in UA is an issue of controversy (Ananth  et al., 2016).    

    In consistence with the other studies, troponin I was tending to have a statistically significant increase from admission to the 6 hours later values, and this occurred in both STEMI and NSTEMI patient groups (Shortt  et al., 2017).                                             

    Our study showed that copeptin values increased directly with troponin I, which in turn increased with increasing mass of infarction, and this was in accordance with other studies (Kavsac, 2017).

    Troponin I was significantly higher in late presenter (>4h) of chest pain than early presenters (<4h), either at admission or 6 hour later. Results were in consistence with the other studies (Kavsac , 2017). 

     Unlike the other studies, this study revealed no significant difference in copeptin levels between early and late presenters of chest pain neither at admission or at 6 hours later. This implied that copeptin was valuable in late as well as early presenters of chest pain. This results made the pattern of copeptin release more questionable, and more studies using more frequent sampling times were warranted to adequately describe its pattern of release. An important factor should be considered in our study that many patients were not accurately able to determine the onset of chest pain. Secondly, we had only a limited number of early presenters compared to late presenters (Vargas  et al. 2016).                                                                                       

Limitations

1. The study was limited by the small sample size, which was further decreased by subgrouping, an effect that was more obvious in NSTEMI patient group. So, the results were only preliminary that need large sample size studies.

2. The troponin I assay used in this study was a second-generation troponin assay.  So, evaluation of copeptin in comparison to highly sensitive troponin was not possible.

3. Only two samples were taken, i.e. on admission and 6 hours later, while frequent the sampling was needed to delineate the pattern of copeptin release after AMI.

4. The effect of thrombolytic therapy on copeptin and troponin I values was not examined, since most of our patient received thrombolysis before referral to NHI or before PCI was done.

5. Being a single center study, our research may be limited by the implausible sample size, lack of blinding, unequal allocation of resources or limited external validity.

6. Management studies were needed to evaluate the safety and effectiveness of this strategy under routine conditions and in a larger number of patients.

7. Due to ethical considerations, copeptin versus troponin values could not be examined neither in stable angina, non-ischemic chest pain nor control cases, as coronary angiography - an essential part of the study to confirm the diagnosis of AMI – would be declined by the aforementioned patient groups after explanation of benefit/ risk considerations. Such an effect is needed to be examined in further studies.

CONCLUSIONS

    The current study provided an evidence that measurement of serum copeptin was better than troponin I for early diagnosis of AMI but could not evaluate the value of copeptin in UA diagnosis versus neither stable coronary artery disease nor non-ischemic causes of chest pain.

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