N-TERMINAL PRO-BRAIN NATRIURETIC PEPTIDE ( NT-proBNP ) SERUM CONCENTRATIONS IN APPARENTLY HEALTHY BOSNIAN WOMEN

Brain natriuretic peptide (BNP) is a cardiac hormone secreted predominantly from the ventricles. Th is hormone is produced as pre-prohormone BNP (pro BNP), than cleaved by corine to biologically active -aminoacid BNP and non-biologically active N-terminal-pro brain natriuretic peptide (NTproBNP). NTproBNP has been found to be a useful marker for the diagnosis of heart failure and left ventricular systolic dysfunction. Recent studies showed that concentration of BNP and NTproBNP predict cardiovascular disease in apparently healthy individuals but their full screening characteristics are not fi rmly established. As NTproBNP serum concentration is altered by numerous factors there are also interindividual variations in NTproBNP values. Th ere are no previous results for Bosnian population so the aim of this study was to asses normal range of NTproBNP serum concentrations in apparently healthy women using electrochemiluminescence immunoassay (Elecsys, Roche Diagnostic). A group of , healthy females, aged , (±,), were enrolled in this study. Mean serum concentration of NTproBNP was , (±,) pg/ml, with the range of , pg/ml (minimum-maximum:,-, pg/ml). We conclude that NTproBNP serum concentration in apparently healthy Bosnian women was not different from the average values of NTproBNP obtained on Europen’s population. Th us, we suggest that the NTproBNP serum upper cut off values measured by using electrochemiluminescence immunoassay “ECLIA” (Elecsys , Roche Diagnostic) for Bosnian females, aged ≤ years, should be  pg/ml as reported by Roche Diagnostic.


Introduction
Brain natriuretic peptide (BNP) is a cardiac hormone secreted predominantly from the ventricles.Th is hormone is produced as pre-prohormone BNP (pro BNP), processed to proBNP, and than cleaved by corine to mature, biologically active -aminoacid BNP and nonbiologically active N-terminal-pro brain natriuretic peptide (NTproBNP) ().Th e natriuretic peptides, especially NTproBNP are increased in conditions with cardiac ventricular volume and pressure overload.Both, plasma levels of brain natriuretic peptide and NTproBNP increase in a variety of cardiovascular conditions ().Also, numerous studies have shown that concentration of BNP and NTproBNP predict cardiovascular disease in apparently healthy individuals although their full screening characteristics are yet to be fi rmly established ().Pre-requisite for NTproBNP screening use is establishment of cut off values in clinical studies which include healthy subjects and also subjects with high risk for cardiovascular diseases.Recent studies showed variations in NTproBNP serum concentration in healthy subjects ().Also, many subjects with raised natriuretic peptide levels had normal systolic function and no overt heart failure.Currently available commercial assays for NT-proBNP are not standardized and consequently the results obtained with assays from different manufacturers may differ markedly ().According to results of the clinical studies performed by Roche diagnostic group each laboratory should investigate the transferability of the expected values to its own patient population and if necessary determine its own reference ranges ().As there are no previous results for Bosnian population the aim of this study was to asses normal range of NT-proBNP serum concentrations in healthy women, aged  years and less using electrochemiluminescence immunoassay "ECLIA" (Elecsys , Roche Diagnostic).

Subjects
Subjects for this study, in total , were selected between persons who have performed regular control of hormonal status at Institute of Nuclear Medicine, University of Sarajevo Clinics Centre.Only women were included, aged  years and less.After an overnight fast, all patients underwent full medical assessment and laboratory examinations.The exclusion criteria were: clinically evident cardiovascular diseases, renal diseases, thyroid disorders, pituitary / hypothalamic disorders, diabetes mellitus, pregnan-cy.The local ethics committee approved the study and the patients gave their written informed consent.NTproBNP measurement Blood samples were collected in the fasting state, immediately put on ice and processed within  minutes.Th ereafter, obtained serum samples were kept frozen at - °C.NTproBNP levels were determined using electrochemiluminescence immunoassay "ECLIA" on Elecsys  (Roche Diagnostic).All measurements were performed at the Institute of Nuclear Medicine, University of Sarajevo Clinics Centre.Th is assay is an electrochemiluminoescent sandwich immunoassay using two polyclonal antibodies directed at the NTproBNP molecule.Th e analytic range extends from - pg/ml.Functional sensitivity was <  pg/ml, defi ned as the lowest analytic concentration that can be reproducibly measured with a between-run coeffi cient of variation .Expected values for women, aged ≤  years are  pg/ml.

Statistical analysis
All data are expressed as means with standard deviation (SD) in table and median, interquartile range and ranges in Figure .Statistical analyses were performed using SPSS . statistical software system.

Results
Subject's physical characteristics are presented in Table .
Data are shown as mean ± SD.

Discussion
Natriuretic peptides are peptide hormones released into the circulation in response to increased myocardial stretch that leads to vasodilatation, natriuresis and inhibition of renin-angiotensin and sympathetic nervous system ().NT proBNP has been found to be a useful marker for the diagnosis of heart failure and left ventricular systolic dysfunction () ).According to their results the average value of NT proBNP was , pmol/l (, pg/ml) with the minimum-maximum range of ,-, pmol/l (,-, pg/ml).
Study of Leowattana et al. () which enrolled  healthy subjects from the checkup department of Bangkok showed that NTproBNP levels increase with aged an that females usually have higher NTproBNP then males (,±, pg/ml vs. ,±, pg/ml).
Shi et al. () have been found lower serum concentration of NTproBNP in apparently healthy Chinese people (< , ng/l for women aged < or= years) than those for western countries.Th ey also concluded that NT-proBNP assay has a good clinical performance for the diagnosis of symptomatic heart failure (HF) but is not suitable as a screening test for HF.
Our results showed that mean serum concentration of NTproBNP in healthy females (Tab.) was , (±,) pg/ml, with the range of , pg/ ml (miminum-maximum:,-, pg/ml) (Fig. .).Our results are in accordance with previously mentioned results obtained from large studies performed on European's population (,).

Conclusion
We conclude that NTproBNP serum concentration in apparently healthy Bosnian women was not diff erent from the average values of NTproBNP obtained on Europen's population.Th us, we suggest that the normal NTproBNP serum upper cut off values measured by using electrochemiluminescence immunoassay "ECLIA" (Elecsys , Roche Diagnostic) for Bosnian females, aged ≤  years, should be  mg/ml as reported by Roche Diagnostic.

TABLE 1 .
Subject' s physical characteristics . Brain natriuretic peptide (BNP) and NTproBNP as inactive but serum stabile component, have been shown to predict cardiovascular disease in apparently healthy individuals.Recent study by Kistrop et al.()showed that measurements of NT-proBNP provide prognostic information of mortality and fi rst major cardiovascular events beyond traditional risk factors.NTproBNP was a stronger risk biomarker for cardiovascular disease than C-reactive protein (CRP) in nonhospitalized individuals aged  to  years.Serum concentration of NTproBNP is altered by diff erent factors: age, gender, race, thyroid hormones, etc.().Screening characteristics of NTproBNP are yet to be established.Th ere are few big clinical studies that resulted in establishing of upper cut off values for NTproBNP.According to data provided from the clinical studies on blood donors performed by Roche diagnostic group (,) upper cut-off values for the women aged  years an less is  pg/ml.Conversely, Reymond et al.()found higher values of NTproBNP serum concentration in women - years old, defi ned as normal subjects (no conges-tive heart failure, no ischaemic heart disease, no history of hypertension, no diabetes, no lung disease, no cardiovascular drug treatment, left ventricular ejection fraction , blood pressure </, and a normal ECG