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COMPARISON OF BNP WITH PRO-BNP IN CHRONIC HEART FAILURE

COMPARISON OF BNP WITH PRO-BNP IN CHRONIC HEART FAILURE. Jones GRD , Boscato L, Bennett S, Macdonald P, Brien J. Departments of Chemical Pathology, Cardiology and Pharmacy, St Vincent’s Hospital, Sydney, Australia. Background: physiology.

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COMPARISON OF BNP WITH PRO-BNP IN CHRONIC HEART FAILURE

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  1. COMPARISON OF BNP WITH PRO-BNP IN CHRONIC HEART FAILURE Jones GRD, Boscato L, Bennett S, Macdonald P, Brien J. Departments of Chemical Pathology, Cardiology and Pharmacy, St Vincent’s Hospital, Sydney, Australia. BNPvproBNP APCCB04

  2. Background: physiology • BNP and NT-proBNP (proBNP) are biomarkers of heart failure. • The molecules are co-secreted but have different clearance pathways. • BNP: receptor mediated, enzymatic degradation, renal, other • ProBNP: renal, other • If concentrations are largely determined by secretion, the analytes should yield similar clinical information. • We evaluate BNP stability with the AxSYM assay and compare BNP with proBNP in serial samples from patients with heart failure. BNPvproBNP APCCB04

  3. Background: Analysis • BNP is a more labile analyte than proBNP • The Abbott BNP assay currently has stability claims for up to 3 months storage at -20 degrees (Product information). • The Roche proBNP kit claims stability up to 12 months at -20 degrees. • Both assays claim stability to freeze/thaw of three cycles although we have previously described stability for five freeze/thaw cycles for proBNP1. REFERENCE 1. Jones GRD, Boscato L, D’Agonstino J, Schneider H-G, Clin Biochem Rev 2002. BNPvproBNP APCCB04

  4. Patients • Heart failure patients were enrolled during hospital admission. • Samples were taken at discharge and at home visit follow-up after 2 weeks, 3 months and 6 months. • Samples were collected in plastic K2EDTA tubes and at -25 degrees. • BNP was measured on an Abbott AxSYM (sample sstored up to 33 months) and ProBNP on a Roche Elecsys (samples stored up to 15 months). • Results for both analytes were reported in pg/mL. BNPvproBNP APCCB04

  5. Stability • AxSYM BNP assays: stored 17 – 33 months • Package insert claim: 3 months at – 20 degrees • Roche proBNP assays: stored 6 - 15 months • Package insert claim: 12 months at -20 degrees • Relationship of BNP to proBNP is used to assess BNP stability. Our data is compared with Abbott data (figure 1). • Conclusion: AxSYM BNP likely to be stable in EDTA plasma stored for nearly three years at -20. Note some individual samples may show greater deterioration. REFERENCE 2. Wu A et al. Am J Cardiol. 2004 BNPvproBNP APCCB04

  6. AxSYM BNP vs Roche NT-proBNP Abbott data Current work N = 101 Y=0.120x + 25 Y=0.168x +47 y = 0.120x + 25 r = 0.849 Figure 1. Relationship of BNP to proBNP, Abbott data and Current data.Interpretation: Current data shows higher BNPs relative to proBNP, indicating BNP stability over storage period. BNPvproBNP APCCB04

  7. BNP:proBNP - patient specificity • There is a wide scatter of results when BNP is plotted against proBNP (Figure 2A). • The data points from individual patients do not show the same degree of scatter (figure 2B). • The ratio of BNP:proBNP is often closely scattered in the samples taken from the same patient (Figure 3). • The total scatter (expressed as CVs) for BNP:proBNP has the following components: • Average within-individual CV: 34% • Average between-individual CV: 58% • Total (group) CV: 69% • Conclusion: Relationship of BNP to proBNP shows marked individuality (Index of Individuality = 0.5). BNPvproBNP APCCB04

  8. BNP vs proBNP Figure 2. BNP v proBNP. A. All data B. Data from patients with 3 or 4 data points. Data points from the same patient are joined. Data is separated according to patient average BNP/proBNP. Note individual scatter is less than group scatter. Average ratio BNP/proBNP:0.22 (CV 66%) mass units0.56 (CV 66%) molar units A BNP B proBNP BNPvproBNP APCCB04

  9. BNP:proBNP - Individual variation BNP/proBNP Patient Figure 3. BNP to proBNP ratios for 64 heart failure patients with 3 or 4 data points available. The red circles are examples of the low within-person variability seen in many patients. BNPvproBNP APCCB04

  10. BNP:proBNP - associations • The discharge BNP:proBNP ratio, as well as the values for proBNP and BNP, were compared with other clinical parameters by univariate comparison (table1). • A number of relationships can be noted: • Negative association of Ratio with ProBNP concentration. Note that this may include a contribution from the effect of renal failure (see below) and may reflect other factors such as conversion of proBNP to BNP (figure 4A). • Positive association of Ratio with creatinine clearance largely due to effect on proBNP (figure 4B). • Strong positive association of proBNP with serum creatinine. • Positive association of ALT with Ratio mainly due to BNP. • Positive association of age with Ratio due to proBNP • Albumin was negatively associated with both measurements. BNPvproBNP APCCB04

  11. BNP: ProBNP - associations Table 1. Correlation coefficients (r) for proBNP, BNP and the BNP:proBNP ratio compared to other available parameters. The results are taken from the samples collected at discharge from hospital. The table is sorted according to the absolute value of the ratio r value. BNPvproBNP APCCB04

  12. BNP:proBNP associations Figure 4. Association of BNP:proBNP ratio with:A. proBNP concentration B. creatinine clearance Data taken from heart failure patients at the time of hospital discharge. A Ratio BNP/proBNP proBNP (ng/L B Creatinine clearance (mL/min) BNPvproBNP APCCB04

  13. Discussion • ProBNP and BNP are thought to be co-secreted. • Differences in the ratio of these analytes may be due to differential clearance of the molecules due to such factors as renal failure. • Different rates of intact proBNP cleavage may also affect the ratio and this current data may be influenced by prolonged storage of the samples prior to analysis. • These factors may contribute to background noise limiting the use of the natriuretic peptides, or may lead to differentiation of the use of these markers. BNPvproBNP APCCB04

  14. Conclusions • The Abbott BNP assay appears to provide stable results for up to 33 months stored at -20 degrees. • The ratio of BNP/proBNP includes both within- and between-person variation. • Multiple factors affect BNP and proBNP concentrations heart failure patients. • Results from these two analytes cannot be used interchangeably in monitoring patients. We acknowledge Abbott and Roche for reagents and equipment. IMPORTANT NOTE: Further data analysis since the time of abstract submission has produced alterations in the interpretations expressed in the abstract. BNPvproBNP APCCB04

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