Understanding cardiac biomarkers in end-stage kidney disease: Frequently asked questions and the promise of clinical application

Troponins, Acute Coronary Syndrome and Renal Disease: From Acute Kidney Injury Through End-stage Kidney Disease

The diagnosis of acute coronary syndromes (ACS) is heavily dependent on cardiac biomarker assays, particularly cardiac troponins. ACS, particularly non-ST segment elevation MI, are more common in patients with acute kidney injury, chronic kidney disease (CKD) and end-stage kidney disease (ESKD), are associated with worse outcomes than in patients without kidney disease and are often difficult to diagnose and treat. Hence, early accurate diagnosis of ACS in kidney disease patients is important using easily available tools, such as cardiac troponins. However, the diagnostic reliability of cardiac troponins has been suboptimal in patients with kidney disease due to possible decreased clearance of troponin with acute and chronic kidney impairment and low levels of troponin secretion due to concomitant cardiac muscle injury related to left ventricular hypertrophy, inflammation and fibrosis. This article reviews the metabolism and utility of cardiac biomarkers in patients with acute and chronic kidney diseases. Cardiac troponins are small peptides that accumulate in both acute and chronic kidney diseases due to impaired excretion. Hence, troponin concentrations rise and fall with acute kidney injury and its recovery, limiting their use in the diagnosis of ACS. Troponin concentrations are chronically elevated in CKD and ESKD, are associated with poor prognosis and decrease the sensitivity and specificity for diagnosis of ACS. Yet, the evidence indicates that the use of high-sensitivity troponins can confirm or exclude a diagnosis of ACS in the emergency room in a significant proportion of kidney disease patients; those patients in whom the results are equivocal may need longer in-hospital assessment.

Prognostic value of the new high sensitive cardiac troponin T assay (hs-cTnT) after coronary artery bypass grafting

Background The aim of the study was to assess the value of post-operative cardiac troponin T-levels, measured with a new highly sensitive assay (hs-cTnT), as a suitable parameter to predict patients' outcome after cardiac surgery. With the introduction of the new hs-cTnT assay the correlation between measured levels and the post-operative patient's outcome remains to be evaluated. Methods Patients undergoing coronary artery bypass grafting (n = 213) were included. Perioperative measurements of hs-cTnT and CK-MB were correlated to parameters of clinical outcome and further explored. Patients with an uneventful course were compared with those with post-operative complications, including need of repeat revascularization (RR) or death (RR/death), cardiogenic shock (CS) or death (CS/death) and a combination of all (RR/CS/death). Results Significant results were observed in patients after isolated CABG, where CS/death and RR/CS/death patients had higher post-operative hs-cTnT levels (P < 0.01). Moreover, multivariate analysis of the CABG-group revealed that acute renal failure (OR =14.7, 95% CI =2.7-79.1, P < 0.001), early post-operative hs-cTnT levels higher than the upper quintile (> 1,476.8 pg/ml) (OR =8.1, 95% CI =3.0-22.2, P < 0.001) and unstable angina pectoris (OR =2.4, 95% CI =1.1-5.7, P < 0.05) were the most powerful independent predictors of post-operative complications. Upon discriminant analysis the application of hs-cTnT almost doubled the sensitivity of the outcome prediction. Conclusions The new hs-cTnT assay is a useful diagnostic tool that may significantly enhance the prediction of adverse events after CABG. In our study a hs-cTnT-value >1,476.8 pg/ml proved to be a reliable marker for ongoing post-operative complications.

Point of care assessment of cardiac troponin T level in CKD patients with chest symptom

We challenged to identify the cutoff value of cTnT in chronic kidney disease (CKD) patients by point of care assessment way. A single center, prospective cross-sectional study was planned and performed. 201 consecutive patients who were visited emergency room for chest symptoms were enrolled in this study. All patients were performed routine practice for differential diagnosis of chest symptom by cardiologist. Simultaneously, semiquantitative measurement of cTnT was performed using same blood sampling on the blind condition to cardiologists for this study. Study patients were divided into four groups according to the estimated glomerular filtration rate (eGFR), CKD1-2, CKD3, CKD4-5, and CKD5D. Usefulness of semiquantitative measurement for diagnosing ACEs was investigated in each group. 77 (38%) of total patient was diagnosed as acute coronary events (ACEs). About 50% of patients were showing cTnT level less than 0.03 ng/mL. The cTnT level over 0.1 ng/mL was found in 30% of total subjects. Mean quantitative value of cTnT was 0.29 ± 0.57 ng/mL in total subjects. Estimated cutoff value in CKD3 patients was 0.088 ng/mL with a sensitivity of 59.3% and specificity of 80.0%. Interestingly, the cutoff values of CKD1-2, CKD4-5, and CKD5D were 0.047, 0.18, and 0.27 respectively, which are half, two times, and three times of CKD3 cutoff value 0.088. The specificities of four cutoff values in each CKD group were showing over 80%, which is higher than sensitivity, respectively. In CKD patients, semiquantitative, point of care assessment of cTnT could be a useful tool for screening for ACEs.

The non-cardiac use and significance of cardiac troponins

Cardiac Troponins are blood markers of myocardial damage and are widely utilised across all acute medical departments. However, with a massive rise in requests for this test, the interpretation of raised serum levels in the absence of cardiac sounding clinical features can become a clinical conundrum. This is especially true if the numerous causes of positive test results are not fully appreciated. A thorough understanding of the strengths and weaknesses of this blood test in light of a patient population living longer, increasing in comorbidities and possible causes of false test results can provide invaluable support in establishing an accurate diagnosis and instigating effective management. This article will describe the history of cardiac markers along with a discussion of the various causes of elevated cardiac troponins outside acute coronary syndrome. It will elaborate on the applications and significance of this blood test and the potential uses of positive results with elevated serum Troponin levels.

Temporal trajectory of B-type natriuretic peptide in patients with CKD stages 3 and 4, dialysis, and kidney transplant

BACKGROUND AND OBJECTIVES

B-type natriuretic peptide (BNP) concentration predicts outcome in patients undergoing dialysis. Because survival and cardiovascular risk change across the CKD continuum, serial changes in BNP were compared in patients at different CKD stages and after kidney transplantation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with CKD stages 3 and 4 (CKD 3-4), dialysis patients, and kidney transplant recipients (KTRs) from one center had two measurements of BNP taken a median of 161 days apart in 2003-2004 and were followed until July 2012. Both BNP-32 (Triage BNP; Biosite Diagnostics) and NT-BNP-76 (proBNP; Roche Diagnostics) were assayed. The interaction between change in log-transformed BNP concentration over time and patient group was tested by fitting regression models on panel data with random effects. Survival after the second measurement was compared by tertile of change in BNP.

RESULTS

Patients with CKD 3-4 (n=48), dialysis patients (n=102), and KTRs (n=73) were followed for a median of 5.7, 4.8, and 5.9 years, respectively. The interaction between patient group and BNP measurements over time was significant for NT-BNP-76 (P<0.001) and BNP-32 (P<0.01). Median NT-BNP-76 increased in dialysis patients and those with CKD 3-4 from 3850 pg/ml (interquartile range [IQR], 1776-12,323 pg/ml) to 18,830 pg/ml (IQR, 6114-61,009 pg/ml; P<0.001) and from 698 pg/ml (IQR, 283-2922 pg/ml) to 2529 pg/ml (IQR, 347-9277 pg/ml; P=0.002), respectively. Change was not significant for KTRs or comparisons made with BNP-32. Survival rate was significantly lower for patients with the highest tertile of change in NT-BNP-76 among patients with CKD 3-4 (P=0.02), but not in the dialysis or KTR groups. In 11 patients who received a kidney transplant during the study, median NT-BNP-76 decreased from 9607 pg/ml (IQR, 2292-31,282 pg/ml) to 457 pg/ml (IQR, 203-863 pg/ml) after transplant (P<0.01).

CONCLUSIONS

The temporal trajectory of BNP differs between dialysis patients and those with CKD 3-4 and KTRs. This has important implications for the development of BNP-guided management strategies in CKD.