Chemical Pathology

Notes

  • N-terminal pro B-type natriuretic peptide (NT-proBNP) is an inactive peptide released along with the active peptide hormone BNP when the walls of the heart are stretched or there is pressure overload on the heart e.g. by fluid overload. BNP then acts on the kidneys causing fluid and sodium loss in the urine and mild vasodilation so releasing the pressure.
  • In heart failure the heart cannot pump strongly enough for the body’s requirements, the heart walls are stretched and fluid starts to accumulate causing back pressure and hence more BNP to be released.
  • NT-proBNP is released into the circulation in equal amounts to the active hormone but is significantly more stable and hence forms a good marker of BNP output.
  • There are many factors which can affect BNP levels (see below) but a low level has been found useful in ruling out heart failure as an explanation of a patient’s symptoms (negative predictive value 97%) so that only patients with a significantly raised level need to be further investigated for this condition.

For primary care requests: please follow the Gloucestershire Heart Failure pathway available on G-care.

For secondary care requests: test is not routinely available except as a rule out test for ECHO. If considered necessary request should first be discussed with a Consultant Cardiologist. If advised by them, please state the name of the Cardiologist on the request form.

Sample requirements

  • If patient on high dose biotin therapy (>5mg/day) collect sample at least 8 hours after the last dose

For adults, 5 ml of blood taken into a narrow gold or rust top tube.

5ml gold tube

Storage/transport

Samples should be sent as soon as possible at ambient temperature to the laboratory but if unavoidable samples can be stored refrigerated overnight.

Required information

Relevant clinical details should be sent with the request, including clinical indication for testing, relevant symptoms and past medical history.

Turnaround times

The assay is run daily Monday to Friday only.

Reference ranges

As per NICE guideline NG106 (2018):

  • An NT‑proBNP level less than 400 pg/ml in an untreated person makes a diagnosis of heart failure less likely
  • An NT‑proBNP level greater than 400 pg/ml is elevated and Heart Failure cannot be excluded. Refer Urgently to Gloucestershire Heart Failure Service
  • An NTproBNP >2000 pg/ml requires urgent referral for ECHO.

Left ventricular hypertrophy, right ventricular overload, ischaemia, tachycardia, hypoxaemia, PE, sepsis, COPD, diabetes, liver cirrhosis, age >70 and eGFR <60 ml/min can all increase NT-proBNP.
Obesity, diuretics, ACE inhibitors, beta blockers, angiotensin receptor antagonists and aldosterone antagonists can lead to falsely low levels although it is felt unlikely to impact on screening but should be factored into clinical judgement when interpreting test results.

Further information

To learn more about NTproBNP visit Lab Tests Online or access the NT-proBNP monograph of the Association for Clinical Biochemistry and Laboratory Medicine

G-Care: Heart Failure information

Page last reviewed: 08/10/2020

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