Diagnostic Use
BNP is a hormone secreted by the overloaded ventricle of the heart. Our lab measures NT-proBNP, which is a byproduct of the secretion of BNP. It differs from BNP in clearance, analytical characteristics and reference intervals. NT-proBNP results are NOT interchangeable with BNP results.
NT-proBNP can be very useful in the assessment of possible heart failure, however it is non-specific and there are many other possible contributing causes including renal impairment, atrial fibrillation, LVH, valvular heart disease, post-myocardial infarction, pulmonary hypertension and older age. NT-proBNP tends to decrease with increased BMI, hypothyroidism, diuretic treatment, vasodilators and ACE-inhibitors.
Even in stable heart failure, there is a lot of within-person biological variability, i.e. a patient’s NT-proBNP result can change significantly from week to week without a significant change in clinical status. An increase or decrease of up to 98% of baseline may be seen due to this biological variation.
Generally it is NOT helpful to repeatedly measure NT-proBNP to monitor acute response to treatment. The test is expensive and should be dictated by clinical need and after consultation with a physician or cardiologist.
Interpretation
See reference intervals below.
Reference Intervals
Units: pmol/L
Ruling out heart failure
A level <35pmol/L strongly rules out heart failure (any age).
Ruling in heart failure
The level which strongly supports heart failure depends on age:
| <50years |
>53 pmol/L
|
| 50-75years |
>106 pmol/L
|
| >75 years |
>212 pmol/L
|
Note that some clinical guidelines use alternate units. To convert between different units, use the following formulae:
| To change from pg/mL to pmol/L |
Multiply by 0.118 |
| To change from ng/L to pmol/L |
Multiply by 0.118 |
| To change from pmol/L to pg/mL |
Multiply by 8.457 |
| To change from pmol/L to ng/L |
Multiply by 8.457 |
Test Method
Performed in: LabPlus Automation
Principle: Sandwich type immunoassay with chemiluminescence detection (ECLIA)
Assay: Roche assay
Analyser: Roche Cobas
Limitations / Interference
Due to a high level of biological variation, small changes in the NT-proBNP level over time (changes of up to 50% may be explained by non-pathological factors).
Uncertainty of Measurement
12% at a level of 9 pmol/L
7% at a level of 40 pmol/L and higher