Troponin I is a better prognostic parameter of cardiovascular events in asymptomatic patients on haemodialysis than troponin T

M. P. Stoffel, M. Pollok and C. A. Baldamus

Medizinische Klinik IV, Universität zu Köln, Köln, Germany

Sir,

Stolear et al. [1] recently published their results on the predictive value of cardiac troponin T (TnT) in 94 patients on regular hemodialysis in end-stage renal disease (ESRD). They reported that TnT is an independent predictor of cardiovascular events and significantly correlates with outcome. In a pilot-study we examined the prevalence and prognostic value of TnT and troponin I (TnI) in 25 asymptomatic patients with chronic renal failure (CRF) (Table 1Go) and nine consecutive patients with acute renal failure (ARF) (Table 2Go) on haemodialysis (HD). Patients with a history of ischaemic heart disease (within the preceding 6 months), chest pain, ECG changes compatible with acute or chronic myocardial ischemia and elevation of CK, CK-MB, AST and LDH were excluded.


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Table 1. Characteristics of 25 patients with chronic renal failure

 

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Table 2. Characteristics of nine patients with acute renal failure

 
Two commercially available test kits were used for detection of TnT (TropT sensitive®, Boehringer Mannheim, sensitivity <0.05 ng/ml) and TnI (Cardiac STATus®, Astra, <0.1 ng/ml) in pre- and postdialysis blood samples. Standard 12-lead electrocardiogram was performed immediately before dialysis treatment and creatine-kinase (CK-MB), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were measured. Low flux bicarbonate haemodialysis (Fresenius F6/F8, Cuprophane dialyzer) was performed in all cases using Fresenius 4008 H dialysis machine. Mean dialysis dosage was 14.3 h/week in all patients (range 12–20.2 h).

TnT was positive in 12 of 25 (48%) patients with CRF and seven of nine (78%) patients with ARF. Both tests were positive in three patients (12%) with CRF and one patient (11%) with ARF. TnI was never elevated without TnT. We followed these TnI positive patients for one year: of the three patients with CRF one died due to fatal myocardial infarction, one underwent coronary artery bypass surgery and one did not develop symptomatic cardiovascular disease. The patient with ARF died also due to a fatal heart attack. TnT was positive in all patients with non-cardiac surgery and three of four patients with septic shock syndrome indicating non-cardiac damage in contrast to the cardiac-muscle specific TnI.

In a meta-analysis of patients with unstable angina TnT and TnI had similar sensitivity and specificity [2]. This has not been shown in patients with ESRD. Van Lente et al. [3] did not find any differences in the predictive value of TnT and TnI in patients with renal insufficiency including patients with serum creatinine of >2 mg/dl and concluded that both parameters have reduced predictive value in renal insufficiency. We found, like others [4,5] that unspecific elevation of TnT is common in uremic patients (56% in our patients, irrespective of cardiovascular disease). This may be due to delayed renal elemination of TnT in ESRD [6]. In uremic patients unspecific expression of TnT in non-cardiac muscle has been demonstrated [7].

Although our study is limited due to the small number of patients enrolled, TnI positivity (in contrast to TnT) was a negative prognostic marker for cardiovascular events. In conclusion, TnI should be routinely used to assess myocardial injury in dialysis patients.

References

  1. Stolear JC, Georges B, Shita A, Verbeelen D. The predictive value of cardiac troponin T measurements in subjects on regular hemodialysis. Nephrol Dialysis Transplant1999; 14: 1961–1967[Abstract/Free Full Text]
  2. Olatidoye AG, Wu AH, Feng YJ, Waters D. Prognostic role of troponin T versus troponin I in unstable angina pectoris for cardiac events with meta-analysis comparing published studies. Am J Cardiol1998; 81: 1405–1410[ISI][Medline]
  3. Van Lente F, McErlean ES, DeLuca SA, Peacock WF, Rao JS, Nissen SE. Ability of troponins to predict adverse outcomes in patients with renal insufficiency and suspected acute coronary syndromes: a case-matched study. J Am Coll Cardiol1999; 33: 471–478[ISI][Medline]
  4. Musso P, Cox I, Vidano E, Zambon D, Panteghani M. Cardiac troponin elevations in chronic renal failure: prevalence and significance. Clin Biochem1999; 32: 125–130[ISI][Medline]
  5. Frankel WL, Herold DA, Ziegler TW, Fitzgerald RL. Cardiac troponin T is elevated in asymptomatic patients with renal failure. Am J Clin Pathol1996; 106: 118–123[ISI][Medline]
  6. Li D, Keffer J, Corry K, Vazquez M, Jialal I. Nonspecific elevation of troponin T levels in patients with chronic renal failure. Clin Biochem1995; 28: 474–477[ISI][Medline]
  7. McLaurin MD, Apple FS, Voss EM, Herzog CA, Sharkey SW. Cardaic troponin I, cardiac troponin T, and creatine kinase MB in dialysis patients without ischemic heart disease: evidence of cardiac troponin T expression in skeletal muscle. Clin Chem1997; 43: 976–982[Abstract/Free Full Text]

 

Reply

J. C. Stolear1 and D. Verbeden2

1 Service de Nephrologie, IMCHO de Tournai, Tournai 2 Service de Nephrologie, A2 UVB, Bruxelles, Belgium

Sir,

Stoffel et al. determined cardiac troponin T (cTnT) and I in a selected group of patients with both acute and chronic renal failure, treated with haemodialysis, by excluding patients who experienced cardiac problems in the previous 6 months. This selection considers a group of patients completely different from ours, namely an unselected dialysis population. The purpose of our study was not to detect acute coronary disease or myocardial infarction. Our aim was to evaluate the factors associated with increased cTnt in dialysis patients and to examine the outcome of those patients. Fifty per cent of the patients included in our study proved to have a cTnT determination >0.10 ng/ml. Of the 24 patients who did not survive the 1-year follow-up period, 20 had an increased cTnT value. Ten patients with a positive cTnT test died from a non-cardiac cause. cTnt also proved to be an independent predictor of outcome in dialysis patients [3]. Others have made similar observations (Table 1Go).


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Table 1.
 
We want to emphasize that myocardial infarction is not the only cause of increased cTnT. Also during sepsis (this is also confirmed by the observation of Stoffel et al.), after coronary surgery and in patients with unstable angina without myocardial infarction an increase in cTnT has been found. cTnT is a test with a high sensitivity but a low specificity in renal failure [3]. Therefore, most authors agree that cTnT on its own is not a valid test for diagnosing myocardial infarction in dialysis patients [15]. Concerning the measurement of cTnI, we do not wish to comment, since we have no experience with this determination in patients on haemodialysis. Lastly, the detection of cTnT in skeletal muscle of patients with renal disease does not necessarily implicate that, if released into the circulation, it would be detectable [6].

References

  1. Ooi DS, Veinot JP, Wells GA, House AA. Increased mortality in hemodialyzed patients with elevated serum troponin T: a one-year outcome study. Clin Biochem1999; 32: 647–652[ISI][Medline]
  2. Porter GA, Norton T, Bennett WB. Troponin T, a predictor of death in chronic haemodialysis patients. Eur Heart J1998; 19 [suppl.]: N34–N37[ISI][Medline]
  3. Stolear JC, Georges B, Shita A, Verbeelen D. The predictive value of cardiac troponin T measurements in subjects on regular haemodialysis. Nephrol Dial Transplant1999; 14: 1961–1967[Abstract/Free Full Text]
  4. Roppolo LP, Fitzgerald R, Dillow J, Ziegler T, Rice M, Maisel A. A comparison of troponin T and troponin I as predictors of cardiac events in patients undergoing chronic hemodialysis at a Veteran's Hospital: a pilot study. J Am Coll Cardiol1999; 34: 448–454[ISI][Medline]
  5. Mockel M, Schindler R, Knorr L, et al. Prognostic value of cardiac troponin T and I elevations in renal disease patients without acute coronary syndromes: a 9-month outcome analysis. Nephrol Dial Transplant1999; 14: 1489–1495[Abstract]
  6. Apple FS, Ricchiuti V, Voss EM, Anderson PA, Ney A, Odland M. Expression of cardiac troponin T isoforms in skeletal muscle of renal disease patients will not cause false-positive serum results by the second generation cardiac troponin T assay. Eur Heart J1998; 19 [Suppl]: N30–N33[ISI][Medline]