An Equation to Explain Variations in Blood NT-ProBNP in Ambulatory Cardiac Subjects
Saranyou Suwanugsorn MD*, Tada Yipintsoi MB, PhD**, Alan F Geater PhD***, Woravut Jintapakorn MD*, Arintaya Phromminthikul MD****
Affiliation : * Department of Medicine, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand ** Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand *** Epidemiology Unit, Faculty of Medicine, Prince of Songkla University, Songkhla, Thailand **** Faculty of Medicine, ChiangMai University, ChiangMai, Thailand
Background : NT-proBNP is being used as a biomarker for prognosticating and delineating cardiac dysfunction.
The cut-off value for deciding normal versus abnormal levels has always been a point of contention since it
depends on the degree of dysfunction as well as other associated conditions often termed non-cardiac factors
and parameters. Such association had not been formally presented.
Objective : To determine the direction and magnitude of effect of cardiac and non-cardiac parameters on
NT-proBNP variability.
Material and Method: The present study included 78 cardiac ambulatory patients with a history of heart
failure and/or low left ventricular ejection fraction. Their cardiac and non-cardiac parameters were recorded
at the time of blood sampling for NT-proBNP. Multivariate linear regression analysis was used to correlate
cardiac and non-cardiac parameters with NT-proBNP level and, from this, a predictive equation was derived.
Results : Log [NT-proBNP (pmol/l)] was 1.424 + 0.348 (for EF of 18-27) + 0.636 (for EF < 18) + 0.021 CTR
- 0.002 SMW - 0.326 for female + 0.430 Cr - 0.010 BW. [EF = LV ejection fraction in %; CTR = cardio-thoracic
ratio in %; SMW = 6-minute walking distance in meters; Cr = serum creatinine in mg/dl; BW = body weight in
kg]. The adjusted R-square for this regression was 0.659. Omitting the non-cardiac variables (sex, Cr, BW)
would decrease the adjusted R-square to 0.493.
Conclusion : Cut-off value for NT-proBNP concentration in subjects without severe systolic heart failure has to
account for these non-cardiac factors.
Keywords : NT-proBNP, Natriuretic peptide, Heart failure, Variability
