Implications of elevated cardiac troponin T in ambulatory patients with heart failure: a prospective analysis.

BACKGROUND: Elevated concentrations of cardiac troponin T (TnT) have been reported in patients hospitalized for decompensated heart failure (HF). We assessed whether elevated TnT levels are associated with the severity, etiology, and prognosis of HF in stable, ambulatory patients. METHODS: From 1998-1999, we prospectively collected data from 136 ambulatory patients with HF, New York Heart Association functional class II to IV, ejection fraction < or =35%, and no recent unstable angina, myocardial infarction, surgery, or coronary revascularization. Blood was obtained and analyzed by immunoassay for TnT, and patients were followed for 14.0 +/- 4.3 months for death or HF hospitalization (primary end point) and other adverse cardiovascular outcomes. RESULTS: Thirty-three patients (24%) had an elevated TnT level (> or =0.02 ng/mL). Mean TnT concentration did not differ by etiology of HF (0.002 +/- 0.03 ng/mL vs 0.02 +/- 0.04 ng/mL for ischemic and nonischemic etiologies, P =.25). Compared with patients with normal (undetectable) levels of TnT, patients with elevated TnT were significantly older, had worse functional class, and had poorer renal function. Elevated TnT concentrations were associated with increased relative risks (RR) of death or HF hospitalization (RR 2.7, 95% CI 1.7-4.3, P =.001) and death alone (RR 4.2, 95% CI 1.8-9.5, P =.001) during follow-up. Elevated TnT and New York Heart Association class were significant, independent predictors of death or HF hospitalization. Increased age and serum creatinine concentrations were significant independent predictors of death alone. CONCLUSIONS: Nearly one fourth of ambulatory patients with chronic HF have ongoing myocardial necrosis as shown by abnormal TnT values, which are associated with increased mortality and morbidity.

Multicenter evaluation of the Roche NT-proBNP assay and comparison to the Biosite Triage BNP assay.

BACKGROUND: Brain natriuretic peptides (BNPs) are useful in the assessment of heart failure, left ventricular dysfunction, and acute coronary syndromes. METHODS: We performed a multicenter evaluation of the automated Roche NT-proBNP assay and compared its performance to the Biosite Triage BNP assay. RESULTS: The N-terminal (1-76) pro brain natriuretic peptide (NT-proBNP) method is precise (CV2-fold higher CV, and plasma samples are more labile when stored at room temperature and 4 degrees C. Comparison studies showed a reasonable correlation between NT-proBNP and BNP assays, with a substantially higher slope bias of 6-20 for the NT-proBNP assay. CONCLUSIONS: The automated Roche NT-proBNP assay has good analytical performance and better precision than the Biosite BNP assay. Unlike BNP, NT-proBNP is stable in EDTA plasma for 3 days at room temperature or longer at 4 degrees C. The Roche NT-proBNP is fully automated and will accommodate the testing of large numbers of clinical samples for assessing cardiac dysfunction.

pH effects on measurements of ionized calcium and ionized magnesium in blood.

CONTEXT: It is well known that the concentration of ionized calcium in blood is affected by the pH of the specimen, since hydrogen ions compete with calcium for binding sites on albumin and other proteins. However, the relationship between pH and ionized magnesium concentration is not as well characterized. OBJECTIVE: To determine the effects of pH on ionized magnesium concentration over a wide range of pH values in serum or plasma. DESIGN: Both ionized calcium and ionized magnesium concentrations were measured in 3 sets of samples. (1) Pools of serum or whole blood at different pH values (7.20-7.60) achieved by adding a constant volume of acid or base (diluted solutions of either hydrochloric acid or sodium hydroxide) plus saline. These pools consisted of 2 serum and 3 heparinized whole blood pools collected from leftover blood remaining in clinical specimens in the Clinical Chemistry and Blood Gas Laboratories, respectively, at Duke University Medical Center. (2) Five whole blood specimens obtained from apparently healthy individual donors. (3) Twenty-six whole blood specimens obtained from individual patients (leftover blood from the Blood Gas Laboratory) in which pH was varied by in vitro loss or gain of carbon dioxide. RESULTS: Both ionized calcium and ionized magnesium concentrations decreased as the pH in the specimen increased, indicating the stronger binding of these ions with proteins in the more alkaline environment. CONCLUSION: We conclude that the rate of change of ionized magnesium concentration with pH change (0.12 mmol/L per pH unit) is significantly less than that of ionized calcium (0.36 mmol/L per pH unit). Furthermore, our findings indicate that if adjustment to pH 7.40 is necessary, the ionized magnesium test results need to be adjusted when pH is markedly abnormal, as is sometimes done for ionized calcium.