Aids in the diagnosis of CHF

 

The role of BNP in monitoring CHF therapy is under investigation.

B-type natriuretic peptide (brain natriuretic peptide [BNP]) is a

32-amino acid-ringed peptide secreted by the heart to regulate

blood pressure and fluid balance.(1) BNP is stored in and secreted

predominantly from membrane granules in the heart ventricles, and

is continuously released from the heart in response to both ventricle

volume expansion and pressure overload.(2)

 

The natriuretic peptide system and the renin-angiotensin system

counteract each other in arterial pressure regulation. When arterial

pressure decreases, the kidneys release renin, which activates

angiotensinogen resulting in increased peripheral resistance of the

arterioles, thus increasing arterial pressure.

 

The natriuretic peptides counteract the effects of rennin secretion,

causing a reduction of blood pressure and in extracellular fluid

volume.(3) Both BNP and ANP (atrial natriuretic peptide) are

activated by atrial and ventricular distension due to increased

intracardiac pressure. These peptides have both natriuretic and

diuretic properties:  they raise sodium and water excretion by

increasing the glomerular filtration rate and inhibiting sodium

reabsorption by the kidney.

 

The New York Heart Association (NYHA) developed a functional

classification system for congestive heart failure (CHF) consisting

of 4 stages based on the severity of the symptoms. Various

studies have demonstrated that circulating BNP concentrations

increase with the severity of CHF based on the NYHA

classification.(4-6)

Males:

      <= 45 years: <= 35 pg/mL

      46 years: <= 36 pg/mL

      47 years: <= 37 pg/mL

      48 years: <= 38 pg/mL

      49 years: <= 39 pg/mL

      50 years: <= 40 pg/mL

      51 years: <= 41 pg/mL

      52 years: <= 42 pg/mL

      53 years: <= 43 pg/mL

      54 years: <= 45 pg/mL

      55 years: <= 46 pg/mL

      56 years: <= 47 pg/mL

      57 years: <= 48 pg/mL

      58 years: <= 49 pg/mL

      59 years: <= 51 pg/mL

      60 years: <= 52 pg/mL

      61 years: <= 53 pg/mL

      62 years: <= 55 pg/mL

      63 years: <= 56 pg/mL

      64 years: <= 57 pg/mL

      65 years: <= 59 pg/mL

      66 years: <= 60 pg/mL

      67 years: <= 62 pg/mL

      68 years: <= 64 pg/mL

      69 years: <= 65 pg/mL

      70 years: <= 67 pg/mL

      71 years: <= 69 pg/mL

      72 years: <= 70 pg/mL

      73 years: <= 72 pg/mL

      74 years: <= 74 pg/mL

      75 years: <= 76 pg/mL

      76 years: <= 78 pg/mL

      77 years: <= 80 pg/mL

      78 years: <= 82 pg/mL

      79 years: <= 84 pg/mL

      80 years: <= 86 pg/mL

      81 years: <= 88 pg/mL

      82 years: <= 91 pg/mL

      >= 83 years: <= 93 pg/mL

Females:

      <= 45 years: <= 64 pg/mL

      46 years: <= 66 pg/mL

      47 years: <= 67 pg/mL

      48 years: <= 69 pg/mL

      49 years: <= 71 pg/mL

      50 years: <= 73 pg/mL

      51 years: <= 74 pg/mL

      52 years: <= 76 pg/mL

      53 years: <= 78 pg/mL

      54 years: <= 80 pg/mL

      55 years: <= 82 pg/mL

      56 years: <= 84 pg/mL

      57 years: <= 87 pg/mL

      58 years: <= 89 pg/mL

      59 years: <= 91 pg/mL

      60 years: <= 93 pg/mL

      61 years: <= 96 pg/mL

      62 years: <= 98 pg/mL

      63 years: <= 101 pg/mL

      64 years: <= 103 pg/mL

      65 years: <= 106 pg/mL

      66 years: <= 109 pg/mL

      67 years: <= 112 pg/mL

      68 years: <= 114 pg/mL

      69 years: <= 117 pg/mL

      70 years: <= 120 pg/mL

      71 years: <= 123 pg/mL

      72 years: <= 127 pg/mL

      73 years: <= 130 pg/mL

      74 years: <= 133 pg/mL

      75 years: <= 137 pg/mL

      76 years: <= 140 pg/mL

      77 years: <= 144 pg/mL

      78 years: <= 147 pg/mL

      79 years: <= 151 pg/mL

      80 years: <= 155 pg/mL

      81 years: <= 159 pg/mL

      82 years: <= 163 pg/mL

      >= 83 years: <=167 pg/mL

>normal <200 pg/mL:  likely compensated CHF

> or =200 to < or =400 pg/mL:  likely moderate CHF

>400 pg/mL:  likely moderate-to-severe CHF

 

BNP levels are loosely correlated with NYHA functional class

(see Table).

 

Table:  Interpretive Levels for CHF

 

Functional Class                5th to 95th Percentile        Median

            I                                   15 to 499 pg/mL                  95 pg/mL

           II                                  10 to 1,080 pg/mL              222 pg/mL

          III                                  38 to >1,300 pg/mL           459 pg/mL

         IV                                   147 to >1,300 pg/mL         1,006 pg/mL

   All CHF                              22 to >1,300 pg/mL           360 pg/mL

 

Elevation in BNP can occur due to right heart failure with

cor pulmonale (200-500 pg/mL), pulmonary hypertension (300-500

pg/mL), and acute pulmonary embolism (150-500 pg/mL).

Elevations also occur in patients with acute coronary syndromes.

Lack of elevations have been reported if CHF is very acute

(first hour) or with ventricular inflow obstruction (hypertrophic

obstructive cardiomyopathy, mitral stenosis, atrial myxoma).

 

Some patients who have been exposed to animal antigens, either

in the environment or as part of treatment or imaging procedures,

may have circulating antianimal antibodies present. These

antibodies may interfere with the assay reagents to produce

unreliable results.

1.   Krishnaswamy, P, Lubien E, Clopton P, et al:  Utility of B-natriuretic

      peptide as a rapid, point-of-care test for screening patients

      undergoing echocardiography to determine left ventricular

      dysfunction. Am J Med  2001;111(4):274-279

 

2.   McNairy M, Gardetto N, Clopton P, et al:  Stability of B-type

      natriuretic peptide levels during exercise in patients with congestive

      heart failure: implications for outpatient monitoring with B-type

      natriuretic peptide. Am Heart J 2002 March;143(3):406-411

 

3.   Redfield MM, Rodeheffer RJ, Mahoney DW, et al:  What is a normal

      BNP? - a community-based study employing two assays for measure-

      ment of BNP. J Card Fail 2001 September;7(3):30