BNP, Plasma

Diagnostic Use

B-type (brain) natriuretic peptide (BNP) is a hormone produced by cardiac myocytes in response to stretch of the cardiac wall. BNP acts on the kidneys to promote salt wasting (natriuresis) and and renal water loss (diuresis) with a subsequent decrease in the circulating plasma volume. BNP also promotes vasodilation, decreasing peripheral vascular resistance and lowering blood pressure.

Plasma BNP is most commonly used as a screening test for heart failure in a patient with dyspnoea. More specialised uses of BNP include prognostication in patients with established heart failure, and in making clinical management decisions regarding heart failure therapy.

Department

Core Biochemistry

Delphic Registration Code

BNP

Synonyms

B type natriuretic peptide

Turnaround Time

3 hours

Test Code

7299

Specimen Type

• Plasma

Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

4.0

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• EDTA (Lavender Cap)

Preferred Sample Volume (ml)

0.6

Aliquot Instructions

Sample Type

• Plasma

Minimum Volume (ml)

0.5

Transport to Lab

Chilled (2 - 8 degrees Celsius)
If overnight - Frozen

Interpretation

In the dyspnoeic patient, BNP results can be interpreted as follows (note that these decision limits apply only to the Beckman Coulter BNP assay currently used at CHL):

Plasma BNP (pmol/L)	Interpretation
<30	Normal.  Heart failure is unlikely
30-80	Equivocal result. Heart failure is possible.  Interpret in the full clinical context
>80	Assuming the presence of supportive symptoms and no reason for a falsely high result (see below), this result is supportive of a diagnosis of heart failure.

There are several other causes of a misleadingly high or low BNP – some of the more common causes are listed below.  Of particular relevance are the neprilysin inhibitor drugs (e.g. sacubitril) which cause large elevations in BNP .

Non-cardiac causes of a low BNP	Non-cardiac causes of a high BNP
Obesity	Renal disease
Hypothyroidism	Liver disease
Drugs – diuretics, ACE inhibitors, vasodilators	Sepsis
	Drugs – neprilysin inhibitors, nesiritide
	Endocrine hypertension (e.g. Cushing’s syndrome, hyperaldosteronism)

Reference Intervals

Adults: 0 – 29 pmol/L

Test Method

Two-site immunoenzymatic (“sandwich”) assay performed on Beckman Coulter DxI 800 analysers with Beckman Coulter reagents.

Non-Funded Test Cost

$52.96 (Exclusive of GST)

Billing Code

7299

Contact Information

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