Clinical use

This assay is indicated for the measurement of NT-proBNP as an aid in the diagnosis and assessment of the severity of heart failure. In patients with acute coronary syndromes (ACS), this test, in conjunction with other known risk factors, can also be used to predict survival as well as to predict the likelihood of future heart failure.

ProBNP is secreted mainly by the ventricle.  It is then cleaved into the physiologically active BNP and the N-terminal fragment NT-proBNP. It is the NT-proBNP molecule that is measured by this assay.

Left ventricular dysfunction (LVD) can occur as part of coronary heart disease, arterial hypertension, valvular disease and primary myocardial disease. If the LVD remains untreated and is progressive the potential for mortality is high. In patients with LVD, plasma levels of BNP and NT-proBNP increase. Studies indicate that measurement of both can be used in the following diagnostic applications:

• Assigning symptoms to cardiac or non-cardiac causes (rule out heart failure).
• Identifying patients with LVD.

NT-proBNP concentration indicates the prognosis of a patient with LVD.

Background

The measurement of NT-proBNP for the diagnosis of heart failure is recommended by NICE guideline NG106 and is also advocated by the Getting It Right First Time (GIRFT) Pathology initiative.

Reference ranges

Age-related NT-proBNP cut-offs are used for supporting a diagnosis of heart failure:

• NT-proBNP >125ng/L in patients <75years old;
• NT-proBNP >450ng/L in paitients 75 years or older.

These cut-offs are used locally for referral to the Heart Failure service. Patients with an NT-proBNP of >2000ng/L should be referred urgently.

Patient preparation

None required

Specimen requirements

Gold top (Serum separating tube) SST

Limitations and restrictions

Patients exposed to animals or animal serum products can produce heterophilic antibodies which can interfere with this assay and produce anomalous results. Results from patients on high-dose biotin therapy, or those taking biotin supplements should be interpreted with caution. Biotin concentrations of 75ng/mL may produce a change in results of up to 10%; higher concentrations can cause falsely depressed NT-proBNP results.

Turnaround time

6 hours

Analysing laboratory

• Biochemistry Lab, James Cook University Hospital, Marton Road, TS4 3BW
• Biochemistry Lab, Friarage Hospital, Northallerton, DL6 1JG